CN110311407A - Cascaded inverter double mode seamless switching control method based on voltage close loop - Google Patents

Cascaded inverter double mode seamless switching control method based on voltage close loop Download PDF

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CN110311407A
CN110311407A CN201910507510.0A CN201910507510A CN110311407A CN 110311407 A CN110311407 A CN 110311407A CN 201910507510 A CN201910507510 A CN 201910507510A CN 110311407 A CN110311407 A CN 110311407A
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current source
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CN110311407B (en
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张兴
毛旺
胡玉华
赵涛
王付胜
李飞
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Hefei Polytechnic University
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The cascaded inverter double mode seamless switching control method based on voltage close loop that the invention discloses a kind of, this method includes current source mode and the mutual method for handover control of voltage source mode.When current source mode switches voltage source mode, by the synchronous Closed loop track for completing modulation wave voltage with Phase synchronization of amplitude, realize inverter by the seamless switching of current source mode to voltage source mode using current feed-forward on this basis.When voltage source mode switching electric current source module, the Closed loop track of modulation wave voltage is completed by modulating wave voltage synchronous adjuster, realizes inverter by the seamless switching of voltage source mode to current source mode using current feed-forward on this basis.This method is able to achieve the seamless switching of two kinds of control models, moreover it is possible to realize the maximum tracking of photovoltaic generation power.

Description

Cascaded inverter double mode seamless switching control method based on voltage close loop
Technical field
The cascaded inverter double mode seamless switching control method based on voltage close loop that the present invention relates to a kind of, belongs to grade Connection type photovoltaic DC-to-AC converter control technology field.
Background technique
Parallel network power generation is and environmental-friendly and be concerned due to providing clean energy resource.In face of how to improve photovoltaic system The problems such as efficiency, reduction cost of electricity-generating of uniting, cascaded H-bridges multi-electrical level inverter is since its modularization is easily expanded, system effectiveness is high, simultaneously Net current total harmonic is distorted the advantages such as small and has become a hot topic of research.
Cascaded H-bridges photovoltaic DC-to-AC converter eliminates the step-up transformer at grid-connected end since its output is directly incorporated into power grid, improves The whole efficiency of photovoltaic generating system.However, extensive grid-connected power generation system is usually mounted to remote districts, and new energy Electricity generation system permeability is also continuously increased, therefore grid-connected power generation system is caused usually to be connected to end weak grid, and this area Domain electric network impedance can usually be sent out because of the variation of the factors such as line impedance, grid-connected unit quantity, load and system operation mode Changing.This under the weak grid of impedance variations characteristic, cascaded H-bridges photovoltaic DC-to-AC converter is adopted since its output impedance is small It is vibrated with conventional current source module and Netease.At this point, using the voltage source grid-connect mode based on sagging control, then it can be real The stability contorting of existing grid-connected inverters.Therefore, research cascaded inverter double mode seamless switching control method has outstanding Engineering significance.
It is ground currently, domestic and foreign scholars have correlation for inverter current source voltage source double mode seamless switching control method Study carefully.As Liang Jiangang, Jin Xinmin, Wu Xuezhi and Tong Yibin are published on " electric power network technique " the 4th phase of volume 38 in April, 2014 " handoff technique of microgrid inverter VCS mode and CCS mode " text.This article is for the energy storage device equal distribution in micro-capacitance sensor Formula power supply has studied the microgrid inverter based on Three-Phase PWM Rectifier topological structure in the PQ current source mode controlled and sagging The mutual handoff technique between voltage source mode is controlled, a kind of method that Closed loop track switches mutually between different mode is proposed. But this method is directed to inverter inverter current source caused under grid-connected and two kinds of operating conditions of off-network and voltage source mode Between mutual switching problem, do not study how inverter realizes current source voltage source double mode seamless switching when grid-connected.This Outside, this method is directed to not study between cascade connection type inverter current source and voltage source mode for centralized inverter Seamless switching.
Extra large treasure of Shi Rongliang, Zhang Xinghe Xu etc. is published on " electrotechnics journal " the 12nd phase of volume 32 in June, 2017 It is proposed whether play is occurred according to mains frequency in " the virtual synchronous generator power control strategy based on adaptive model switching " It is strong to fluctuate to switch the control model of microgrid energy storage inverter.Inverter work is set to exist when fluctuation occurs for mains frequency Current source mode prevents energy-storage battery overshoot or over-discharge from extending the energy-storage battery service life.Base is then used when mains frequency is normal In the voltage source mode of sagging control, the stream of microgrid energy storage inverter in parallel is realized.But this method is directed in three-phase set Formula energy storage inverter, does not study cascaded inverter.Further, since its DC side is energy-storage battery, photovoltaic power generation function is not studied The maximum tracking of rate.
Document " A Novel Stability Improvement Strategy for a Multi- in 2018 Inverter System in a Weak Grid Utilizing Dual-Mode Control”Ming Li,Xing Zhang And Wei Zhao, " energies ", 2018,11 (8), 2144-2162 (" improve multi-inverter under a kind of novel weak grid System stability two-mode field strategy ", " energy periodical " the 8th 2144-2162 pages of phase of volume 11 in 2018) propose that one kind is based on The switching mode of the stagnant ring of impedance improves the stability of multiple inverter system.But this method does not study inverter in current source mode Or the maximum tracking of photovoltaic generation power how is realized under voltage source mode.In addition, this method is directed to three-phase centralization Inverter is not directed to cascade connection type photovoltaic DC-to-AC converter.
In conclusion existing cascaded H-bridges photovoltaic combining inverter current source voltage source double mode seamless switching control method It is primarily present following problem:
(1) the inverter current source voltage source double mode method for handover control spininess of prior art research is to inverter simultaneously Mutual switching problem under two kinds of operating conditions of net and off-network between caused inverter current source and voltage source mode, shorter mention How inverter realizes current source voltage source double mode seamless switching when grid-connected.
(2) the inverter current source voltage source double mode method for handover control spininess of prior art research is to three-phase centralization Energy storage inverter not can relate to cascade connection type photovoltaic DC-to-AC converter.
(3) the inverter current source voltage source double mode method for handover control spininess of prior art research is to inverter direct current Side is stable power supply, does not consider the maximal power tracing of photovoltaic power generation.
Summary of the invention
The problem to be solved in the present invention is exactly to overcome the limitation of above scheme, for Cascade-type photovoltaic grid-connected inverter electricity Stream source voltage source double mode switches this problem, proposes a kind of cascaded inverter double mode seamless switching based on voltage close loop Control method.This method, which uses, is based on voltage close loop control mode, is not only able to achieve Cascade-type photovoltaic grid-connected inverter current source Voltage source double mode seamless switching, and it is able to achieve the maximal power tracing of each H-bridge unit photovoltaic power generation.
To solve technical problem of the invention, the present invention provides a kind of cascaded inverter double mode based on voltage close loop Seamless switching control method, the cascaded inverter is by N number of H-bridge unit with photovoltaic module, filter inductance LSAnd filter Wave capacitor CfComposition, which is characterized in that this control method include current source mode seamless switching voltage source mode control method and Voltage source mode seamless switching current source mode control method:
The current source mode seamless switching voltage source mode control method the following steps are included:
Step 1, the DC voltage of each H-bridge unit is sampled and is successively filtered by 100Hz trapper, obtain N number of H The DC voltage actual value of bridge unit is simultaneously denoted as VPVi, i=1,2,3...N；The DC side electric current for sampling N number of H-bridge unit is practical It is worth and is denoted as IPVi, i=1,2,3...N；Sampling filter inductive current actual value is simultaneously denoted as IL；Sampling filter capacitance voltage is practical It is worth and is denoted as Vo；Sampling power network current actual value is simultaneously denoted as IS；
Step 2, by each H-bridge unit DC voltage actual value VPViMPPT maximum power point tracking control is carried out, is obtained The DC voltage instruction value of N number of H-bridge unit is simultaneously denoted as VPVi *, wherein i=1,2,3...N；
Step 3, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PViThe N number of H obtained with step 2 The DC voltage instruction value V of bridge unitPVi *, by direct current voltage regulator under current source mode, current source mould is calculated The active-power P of each H-bridge unit under formulaCi, wherein i=1,2,3...N, calculating formula are as follows:
Wherein, KCVPFor direct current voltage regulator proportionality coefficient, K under current source modeCVIFor direct current under current source mode Adjuster integral coefficient is pressed, i=1,2,3...N, s are Laplace operator；
Step 4, the active-power P of N number of H-bridge unit under the current source mode obtained according to step 3CiCurrent source is calculated The sum of active power of N number of H-bridge unit and P is denoted as under modeCT, calculating formula are as follows:
Step 5, to the filter capacitor voltage actual value V sampled in step 1oIt carries out locking phase and obtains grid voltage amplitude VmWith Phase thetag；The filter capacitor voltage actual value V that will be sampled in step 1 by virtual synchronous rotating coordinate transformationoIt is converted into revolving Turn the current source mode filter capacitor voltage active component V under coordinate systemCodWith current source mode filter capacitor voltage power-less component VCoq；The filter inductance current actual value I that will be sampled in step 1 by virtual synchronous rotating coordinate transformationLIt is converted into rotating Current source mode filter inductance active component of current I under coordinate systemCLdWith the current source mode filter inductance reactive component of current ICLq；
Step 6, the sum of active power of N number of H-bridge unit P under the current source mode obtained according to step 4CTIt is obtained with step 5 The grid voltage amplitude V arrivedmFilter inductance active component of current reference value under current source mode is calculatedIts calculating formula Are as follows:
Step 7, the current source mode filter inductance active component of current I obtained according to step 5CLd, current source mode filtering Inductive current reactive component ICLqFilter inductance active component of current reference value under the current source mode obtained with step 6Respectively By reactive current adjuster under watt current adjuster under current source mode and current source mode, current source mode is calculated Lower d axis PI regulated value ECdWith q axis PI regulated value E under current source modeCq, calculating formula is respectively as follows:
Wherein, KCiPFor current regulator proportionality coefficient, K under current source modeCiIFor current regulator under current source mode Integral coefficient；
Step 8, d axis PI regulated value E under the current source mode obtained according to step 7Cd, q axis PI is adjusted under current source mode Value ECqThe current source mode filter capacitor voltage active component V obtained with step 5Cod, current source mode filter capacitor voltage power-less Component VCoqAnti- coordinate transform is rotated by virtual synchronous obtain inverter under current source mode always modulate wave voltage VCr；
Step 9, the active-power P of N number of H-bridge unit under the current source mode obtained according to step 3CiIt is obtained with step 4 The sum of active power of N number of H-bridge unit P under current source modeCTThe power distribution system of each H-bridge unit under calculating current source module Number FactorCi, i=1,2,3...N, calculating formula are as follows:
Step 10, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, electric current that step 8 obtains Inverter always modulates wave voltage V under source moduleCrN number of H-bridge unit power partition coefficient under the current source mode obtained with step 9 FactorCi, the modulation wave voltage V of each H-bridge unit under calculating current source moduleCri, i=1,2,3...N, calculating formula are as follows:
Step 11, it before switching, latches filter inductance active component of current reference value under upper periodic current source module and is denoted asIt latches N number of H-bridge unit power partition coefficient under upper periodic current source module and is denoted as FactorCmi, it is calculated each Direct current voltage regulator feedforward control amount I under voltage source modeVFeedi, i=1,2,3...N, calculating formula are as follows:
Step 12, before switching, d axis PI regulated value E under the current source mode obtained according to step 7Cd, q under current source mode Axis PI regulated value ECqThe current source mode filter capacitor voltage active component V obtained with step 5CodCurrent source mode is calculated Lower inverter always modulates the amplitude V of wave voltageCrmAnd phase thetaCr, calculating formula are as follows:
Step 13, the filter capacitor voltage actual value V that will be sampled in step 1oBecome by virtual synchronous rotational coordinates Change the voltage source mode filter capacitor voltage active component V being converted under rotating coordinate systemVodWith voltage source mode filter capacitor electricity Press reactive component VVoq；
Step 14, the power network current actual value I that will be sampled in step 1STurned by virtual synchronous rotating coordinate transformation Change the voltage source mode power network current active component I under rotating coordinate system intoVSdWith voltage source mode power network current reactive component IVSq；
Step 15, the voltage source mode filter capacitor voltage active component V obtained according to step 13Vod, voltage source mode filter Wave capacitance voltage reactive component VVoqThe voltage source mode power network current active component I obtained with step 14VSd, voltage source mode electricity Net reactive component of current IVSq, by calculating and filtering through low-pass first order filter, it is flat to obtain inverter output under voltage source mode Equal active-power PVoWith average reactive power QVo, calculating formula are as follows:
Wherein, τ is low-pass first order filter time constant；
Step 16, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, N number of H that step 2 obtains The DC voltage instruction value V of bridge unitPVi *Direct current voltage regulator feedforward control under the N number of voltage source mode obtained with step 11 Amount I processedVFeedi, by direct current voltage regulator under voltage source mode, each H-bridge unit under voltage source mode is calculated has Function power PVi, wherein i=1,2,3...N, calculating formula are as follows:
Wherein, KVVPFor direct current voltage regulator proportionality coefficient, K under voltage source modeVVIFor direct current under voltage source mode Pressure adjuster integral coefficient, i=1,2,3...N；
Step 17, the active-power P of N number of H-bridge unit under the voltage source mode obtained according to step 16ViVoltage is calculated The sum of active power of N number of H-bridge unit and P is denoted as under source moduleVT, calculating formula are as follows:
Step 18, the sum of active power of N number of H-bridge unit P under the voltage source mode obtained according to step 17VTWith step 15 Inverter exports average active power P under obtained voltage source modeVoIt is calculated through active power-frequency droop governing equation The output angular frequency of inverter under voltage source modeVo, angular frequency is exported under voltage source modeVoVoltage is obtained by integral The output phase angle theta of inverter under source moduleVo, active power-frequency droop governing equation are as follows:
ωVo=ω*+m(PVT-PVo)
Wherein ω*For synchronized angular frequency, m is active sagging coefficient；
Step 19, inverter exports average reactive power Q under the voltage source mode obtained according to step 15VoThrough idle function Filter capacitor voltage active component reference value under voltage source mode is calculated in the sagging governing equation of rate-voltageAnd voltage source Filter capacitor voltage power-less component reference value under modeIts sagging governing equation of reactive power-voltage are as follows:
Wherein E is with reference to electromotive force, and n is idle sagging coefficient, Q*Reactive power instruction is given for upper layer；
Step 20, inverter always modulates the amplitude V of wave voltage under the current source mode obtained according to step 12CrmAnd phase θCr, the output phase angle theta of inverter under the voltage source mode that step 18 obtainsVoAnd it is filtered under the obtained voltage source mode of step 19 Wave capacitance voltage active component reference valueIt is adjusted in synchronism respectively by Phase synchronization adjuster under voltage source mode and amplitude Device, inverter always modulates the amplitude V of wave voltage under voltage source mode when switching is calculatedVrmAnd phase thetaVr, calculating formula are as follows:
Wherein, KVSP1For amplitude synchronous governor proportionality coefficient, K under voltage source modeVSI1It is same for amplitude under voltage source mode Walk adjuster integral coefficient, KVSP2For Phase synchronization adjuster proportionality coefficient, K under voltage source modeVSI2For phase under voltage source mode Bit synchronization adjuster integral coefficient；
Step 21, the active-power P of N number of H-bridge unit under the voltage source mode obtained according to step 16ViIt is obtained with step 17 Voltage source mode under N number of H-bridge unit the sum of active power PVTCalculate the power distribution of each H-bridge unit under voltage source mode Coefficient FactorVi, i=1,2,3...N, calculating formula are as follows:
Step 22, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, what step 20 obtained cuts Inverter always modulates the amplitude V of wave voltage under voltage source mode when changingVrmAnd phase thetaVrAnd the voltage source mode that step 21 obtains Under N number of H-bridge unit power partition coefficient FactorVi, when switching is calculated under voltage source mode each H-bridge unit modulating wave Voltage VVri, i=1,2,3...N, calculating formula are as follows:
The voltage source mode seamless switching current source mode control method includes:
Firstly, starting modulating wave voltage synchronous adjuster, filtered electrical under the voltage source mode that step 19 is obtained before switching Hold voltage active component reference valueD axis PI regulated value under the upper periodic current source module that step 7 obtainsWith step 5 Obtained current source mode filter capacitor voltage active component VCodIt obtains switching preceding electric current by modulating wave voltage synchronous adjuster Filter inductance active component of current reference value under source moduleIts calculating formula are as follows:
Wherein, KCSPFor current source mode modulated wave voltage synchronous governor proportionality coefficient, KCSIFor under current source mode Modulating wave voltage synchronous adjuster integral coefficient；
Secondly, latching under upper periodic voltage source module active point of filter inductance electric current after the completion of modulating wave voltage synchronous Amount reference value is denoted asIt latches N number of H-bridge unit power partition coefficient under upper periodic voltage source module and is denoted as FactorVmi, Direct current voltage regulator feedforward control amount I under each current source mode is calculatedCFeedi, i=1,2,3...N, calculating formula Are as follows:
Finally, by direct current voltage regulator feedforward control amount I under current source modeCFeediIt is superimposed upon each current source mode The output of lower direct current voltage regulator, when switching is calculated under current source mode each H-bridge unit active-power P 'Ci, Middle i=1,2,3...N, calculating formula are as follows:
Compared with prior art, a kind of cascaded inverter double mode based on voltage close loop disclosed by the invention is without seaming and cutting Control method is changed, realizes the seamless of cascaded H-bridges photovoltaic combining inverter two-mode field using based on voltage close loop control strategy Switching, its advantages are embodied in:
1, cascade connection type photovoltaic DC-to-AC converter may be implemented in two kinds of control moulds of current source and voltage source in method proposed by the present invention Seamless switching between formula.
2, method proposed by the present invention can make cascade connection type photovoltaic DC-to-AC converter in two kinds of control models of current source and voltage source Under be able to achieve the maximum tracking of photovoltaic generation power.
3, double mode switching method proposed by the present invention is simple, is easy to Project Realization.
Detailed description of the invention
Fig. 1 is cascaded inverter main circuit topology block diagram of the present invention.
Fig. 2 is the master control block diagram of cascaded inverter double mode switching of the present invention.
Fig. 3 is using cascaded inverter when control method of the present invention by current source mode switching voltage source mode power grid electricity Flow ISAnd each H-bridge unit DC voltage waveform.
Fig. 4 is using cascaded inverter when control method of the present invention by voltage source mode switching electric current source module power grid electricity Flow ISAnd each H-bridge unit DC voltage waveform.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right Present invention work further clearly and completely describes.
Fig. 1 be cascaded inverter of embodiment of the present invention topological structure, as shown in the figure, the cascaded inverter by N number of H-bridge unit with photovoltaic module, filter inductance LSWith filter capacitor CfComposition.Specifically, N number of H-bridge unit DC side according to It is secondary with N number of photovoltaic battery panel PV1, PV2...PVN connection, photovoltaic battery panel operating condition is at 25 DEG C of rated temperature, normal light According to intensity 1000W/m2Under maximum power point voltage be 30.40V, every piece of photovoltaic battery panel passes through 14.1mF capacitor and each H Bridge unit is connected, and cascade system passes through 1.5mH filter inductance LSWith 55uF filter capacitor CfIt is connected to power grid.
Double mode switching master control block diagram of the invention is as shown in Figure 2.
Current source mode seamless switching voltage source mode control method the following steps are included:
Step 1, the DC voltage of each H-bridge unit is sampled and is successively filtered by 100Hz trapper, obtain N number of H The DC voltage actual value of bridge unit is simultaneously denoted as VPVi, i=1,2,3...N；The DC side electric current for sampling N number of H-bridge unit is practical It is worth and is denoted as IPVi, i=1,2,3...N；Sampling filter inductive current actual value is simultaneously denoted as IL；Sampling filter capacitance voltage is practical It is worth and is denoted as Vo；Sampling power network current actual value is simultaneously denoted as IS；
In the present embodiment, by taking five H-bridge units as an example, DC voltage actual value when each H-bridge unit is initial is VPV1 =VPV2=VPV3=VPV4=VPV5=35V.
Step 2, by each H-bridge unit DC voltage actual value VPViMPPT maximum power point tracking control is carried out, is obtained The DC voltage instruction value of N number of H-bridge unit is simultaneously denoted as VPVi *, wherein i=1,2,3...N；
In the present embodiment, when initial time t=0.8s, each H-bridge unit works at T=25 DEG C of rated temperature, normal light According to intensity E1=E2=E3=E4=E5=1000W/m2Under conditions of, obtain the DC voltage instruction value of each H-bridge unit VPV1 *=VPV2 *=VPV3 *=VPV4 *=VPV5 *=30.40V.In t=1s, temperature is remained unchanged, and the illumination of the 3rd, 4,5 H bridge is strong Degree remains unchanged, and the intensity of illumination of the 1st, 2 H bridge becomes E respectively1=E2=800W/m2, obtain the DC side of each H-bridge unit Voltage instruction value VPV1 *=VPV2 *=30.57V, VPV3 *=VPV4 *=VPV5 *=30.40V.
Step 3, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PViThe N number of H obtained with step 2 The DC voltage instruction value V of bridge unitPVi *, by direct current voltage regulator under current source mode, current source mould is calculated The active-power P of each H-bridge unit under formulaCi, wherein i=1,2,3...N, calculating formula are as follows:
Wherein, KCVPFor direct current voltage regulator proportionality coefficient, K under current source modeCVIFor direct current under current source mode Adjuster integral coefficient is pressed, i=1,2,3...N, s are Laplace operator.Direct current voltage regulator ratio under current source mode Coefficient and integral coefficient are designed according to conventional gird-connected inverter, in the present embodiment, KCVP=1, KCVI=10.
Step 4, the active-power P of N number of H-bridge unit under the current source mode obtained according to step 3CiCurrent source is calculated The sum of active power of N number of H-bridge unit and P is denoted as under modeCT, calculating formula are as follows:
Step 5, to the filter capacitor voltage actual value V sampled in step 1oIt carries out locking phase and obtains grid voltage amplitude VmWith Phase thetag；The filter capacitor voltage actual value V that will be sampled in step 1 by virtual synchronous rotating coordinate transformationoIt is converted into revolving Turn the current source mode filter capacitor voltage active component V under coordinate systemCodWith current source mode filter capacitor voltage power-less component VCoq；The filter inductance current actual value I that will be sampled in step 1 by virtual synchronous rotating coordinate transformationLIt is converted into rotating Current source mode filter inductance active component of current I under coordinate systemCLdWith the current source mode filter inductance reactive component of current ICLq, calculating formula is respectively as follows:
Wherein k1For gain coefficient.In the present embodiment, k1=0.5.
Step 6, the sum of active power of N number of H-bridge unit P under the current source mode obtained according to step 4CTIt is obtained with step 5 The grid voltage amplitude V arrivedmFilter inductance active component of current reference value under current source mode is calculatedIts calculating formula Are as follows:
Step 7, the current source mode filter inductance active component of current I obtained according to step 5CLd, current source mode filtering Inductive current reactive component ICLqFilter inductance active component of current reference value under the current source mode obtained with step 6Point Not Tong Guo reactive current adjuster under watt current adjuster and current source mode under current source mode, current source mould is calculated D axis PI regulated value E under formulaCdWith q axis PI regulated value E under current source modeCq, calculating formula is respectively as follows:
Wherein, KCiPFor current regulator proportionality coefficient, K under current source modeCiIFor current regulator under current source mode Integral coefficient.Current regulator proportionality coefficient and integral coefficient are designed according to conventional gird-connected inverter under current source mode, In the present embodiment, KCiP=4, KCiI=20.
Step 8, d axis PI regulated value E under the current source mode obtained according to step 7Cd, q axis PI is adjusted under current source mode Value ECqThe current source mode filter capacitor voltage active component V obtained with step 5CodAnti- coordinate transform is rotated by virtual synchronous It obtains inverter under current source mode and always modulates wave voltage VCr, calculating formula are as follows:
VCr=(ECd+VCod)cosθg+ECqsinθg
Step 9, the active-power P of N number of H-bridge unit under the current source mode obtained according to step 3CiIt is obtained with step 4 The sum of active power of N number of H-bridge unit P under current source modeCTThe power distribution system of each H-bridge unit under calculating current source module Number FactorCi, i=1,2,3...N, calculating formula are as follows:
Step 10, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, electric current that step 8 obtains Inverter always modulates wave voltage V under source moduleCrN number of H-bridge unit power partition coefficient under the current source mode obtained with step 9 FactorCi, the modulation wave voltage V of each H-bridge unit under calculating current source moduleCri, i=1,2,3...N, calculating formula are as follows:
Step 11, it before switching, latches filter inductance active component of current reference value under upper periodic current source module and is denoted asIt latches N number of H-bridge unit power partition coefficient under upper periodic current source module and is denoted as FactorCmi, it is calculated each Direct current voltage regulator feedforward control amount I under voltage source modeVFeedi, i=1,2,3...N, calculating formula are as follows:
Step 12, before switching, d axis PI regulated value E under the current source mode obtained according to step 7Cd, q under current source mode Axis PI regulated value ECqThe current source mode filter capacitor voltage active component V obtained with step 5CodCurrent source mode is calculated Lower inverter always modulates the amplitude V of wave voltageCrmAnd phase thetaCr, calculating formula are as follows:
Step 13, the filter capacitor voltage actual value V that will be sampled in step 1oBecome by virtual synchronous rotational coordinates Change the voltage source mode filter capacitor voltage active component V being converted under rotating coordinate systemVodWith voltage source mode filter capacitor electricity Press reactive component VVoq, calculating formula are as follows:
Wherein θ 'VoFor the output phase angle of inverter under upper periodic voltage source module, k2For gain coefficient.The present embodiment In, k2=0.5.
Step 14, the power network current actual value I that will be sampled in step 1STurned by virtual synchronous rotating coordinate transformation Change the voltage source mode power network current active component I under rotating coordinate system intoVSdWith voltage source mode power network current reactive component IVSq, calculating formula are as follows:
Wherein k3For gain coefficient, in the present embodiment, k3=0.5.
Step 15, the voltage source mode filter capacitor voltage active component V obtained according to step 13Vod, voltage source mode filter Wave capacitance voltage reactive component VVoqThe voltage source mode power network current active component I obtained with step 14VSd, voltage source mode electricity Net reactive component of current IVSq, by calculating and filtering through low-pass first order filter, it is flat to obtain inverter output under voltage source mode Equal active-power PVoWith average reactive power QVo, calculating formula are as follows:
Wherein, τ is low-pass first order filter time constant, in the present embodiment, τ=1e-4s.
Step 16, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, N number of H that step 2 obtains The DC voltage instruction value V of bridge unitPVi *Direct current voltage regulator feedforward control under the N number of voltage source mode obtained with step 11 Amount I processedVFeedi, by direct current voltage regulator under voltage source mode, each H-bridge unit under voltage source mode is calculated has Function power PVi, wherein i=1,2,3...N, calculating formula are as follows:
Wherein, KVVPFor direct current voltage regulator proportionality coefficient, K under voltage source modeVVIFor direct current under voltage source mode Pressure adjuster integral coefficient, i=1,2,3...N.Direct current voltage regulator proportionality coefficient and integral coefficient are pressed under voltage source mode More solito gird-connected inverter is designed, in the present embodiment, KVVP=0.05, KVVI=40.
Step 17, the active-power P of N number of H-bridge unit under the voltage source mode obtained according to step 16ViVoltage is calculated The sum of active power of N number of H-bridge unit and P is denoted as under source moduleVT, calculating formula are as follows:
Step 18, the sum of active power of N number of H-bridge unit P under the voltage source mode obtained according to step 17VTWith step 15 Inverter exports average active power P under obtained voltage source modeVoIt is calculated through active power-frequency droop governing equation The output angular frequency of inverter under voltage source modeVo, angular frequency is exported under voltage source modeVoVoltage is obtained by integral The output phase angle theta of inverter under source moduleVo, active power-frequency droop governing equation are as follows:
ωVo=ω*+m(PVT-PVo)
Wherein ω*For synchronized angular frequency, m is active sagging coefficient.Synchronized angular frequency in the present embodiment*= 100 π rad/s, active sagging Coefficient m=6.28e-3rad/W.
Step 19, inverter exports average reactive power Q under the voltage source mode obtained according to step 15VoThrough idle function Filter capacitor voltage active component reference value V under voltage source mode is calculated in the sagging governing equation of rate-voltageV * odAnd voltage source Filter capacitor voltage power-less component reference value V under modeV * oq, the sagging governing equation of reactive power-voltage are as follows:
Wherein E is with reference to electromotive force, and n is idle sagging coefficient, Q*Reactive power instruction is given for upper layer.In the present embodiment With reference to electromotive force E=120V, idle sagging coefficient n=5e-3V/Var, upper layer gives reactive power and instructs Q*=0Var.
Step 20, inverter always modulates the amplitude V of wave voltage under the current source mode obtained according to step 12CrmAnd phase θCr, the output phase angle theta of inverter under the voltage source mode that step 18 obtainsVoAnd it is filtered under the obtained voltage source mode of step 19 Wave capacitance voltage active component reference valueIt is adjusted in synchronism respectively by Phase synchronization adjuster under voltage source mode and amplitude Device, inverter always modulates the amplitude V of wave voltage under voltage source mode when switching is calculatedVrmAnd phase thetaVr, calculating formula are as follows:
Wherein, KVSP1For amplitude synchronous governor proportionality coefficient, K under voltage source modeVSI1It is same for amplitude under voltage source mode Walk adjuster integral coefficient, KVSP2For Phase synchronization adjuster proportionality coefficient, K under voltage source modeVSI2For phase under voltage source mode Bit synchronization adjuster integral coefficient.In the present embodiment, KVSP1=0.5, KVSI1=2, KVSP2=40, KVSI2=200.
Step 21, the active-power P of N number of H-bridge unit under the voltage source mode obtained according to step 16ViIt is obtained with step 17 Voltage source mode under N number of H-bridge unit the sum of active power PVTCalculate the power distribution of each H-bridge unit under voltage source mode Coefficient FactorVi, i=1,2,3...N, calculating formula are as follows:
Step 22, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, what step 20 obtained cuts Inverter always modulates the amplitude V of wave voltage under voltage source mode when changingVrmAnd phase thetaVrAnd the voltage source mode that step 21 obtains Under N number of H-bridge unit power partition coefficient FactorVi, when switching is calculated under voltage source mode each H-bridge unit modulating wave Voltage VVri, i=1,2,3...N, calculating formula are as follows:
The voltage source mode seamless switching current source mode control method includes:
Firstly, starting modulating wave voltage synchronous adjuster, filtered electrical under the voltage source mode that step 19 is obtained before switching Hold voltage active component reference valueD axis PI regulated value under the upper periodic current source module that step 7 obtainsWith step 5 Obtained current source mode filter capacitor voltage active component VCodIt obtains switching preceding electric current by modulating wave voltage synchronous adjuster Filter inductance active component of current reference value under source moduleIts calculating formula are as follows:
Wherein, KCSPFor current source mode modulated wave voltage synchronous governor proportionality coefficient, KCSIFor under current source mode Modulating wave voltage synchronous adjuster integral coefficient.In the present embodiment, KCSP=0.2, KCSI=20.
Secondly, latching under upper periodic voltage source module active point of filter inductance electric current after the completion of modulating wave voltage synchronous Amount reference value is denoted asIt latches N number of H-bridge unit power partition coefficient under upper periodic voltage source module and is denoted as FactorVmi, Direct current voltage regulator feedforward control amount I under each current source mode is calculatedCFeedi, i=1,2,3...N, calculating formula Are as follows:
Finally, by direct current voltage regulator feedforward control amount I under current source modeCFeediIt is superimposed upon each current source mode The output of lower direct current voltage regulator, when switching is calculated under current source mode each H-bridge unit active-power P 'Ci, Middle i=1,2,3...N, calculating formula are as follows:
Fig. 3 is to switch voltage source mode power grid electricity by current source mode using cascaded inverter when control method of the present invention Flow ISAnd each H-bridge unit DC voltage waveform.Voltage source mode is switched by current source mode in 1.5s, when 1.54s completes Switching, power network current do not impact, inverter seamless switching.Each H-bridge unit DC voltage is controlled at it after the completion of switching DC voltage instruction value VPVi *Place, i=1,2,3...N, i.e., at each H-bridge unit maximum power point.
Fig. 4 is using cascaded inverter when control method of the present invention by voltage source mode switching electric current source module power grid electricity Flow ISAnd each H-bridge unit DC voltage waveform.In 2s by voltage source mode switching electric current source module, when 2.04s, completes to cut It changes, power network current does not impact, inverter seamless switching.Each H-bridge unit DC voltage controls straight at it after the completion of switching Flow side voltage instruction value VPVi *Place, i=1,2,3...N, i.e., at each H-bridge unit maximum power point.

Claims (1)

1. a kind of cascaded inverter double mode seamless switching control method based on voltage close loop, the cascaded inverter By N number of H-bridge unit with photovoltaic module, filter inductance LSWith filter capacitor CfComposition, which is characterized in that this control method packet Include current source mode seamless switching voltage source mode control method and voltage source mode seamless switching current source mode control method:
The current source mode seamless switching voltage source mode control method the following steps are included:
Step 1, the DC voltage of each H-bridge unit is sampled and is successively filtered by 100Hz trapper, obtain N number of H bridge list The DC voltage actual value of member is simultaneously denoted as VPVi, i=1,2,3...N；Sample the DC side current actual value of N number of H-bridge unit simultaneously It is denoted as IPVi, i=1,2,3...N；Sampling filter inductive current actual value is simultaneously denoted as IL；Sampling filter capacitance voltage actual value is simultaneously It is denoted as Vo；Sampling power network current actual value is simultaneously denoted as IS；
Step 2, by each H-bridge unit DC voltage actual value VPViMPPT maximum power point tracking control is carried out, N number of H is obtained The DC voltage instruction value of bridge unit is simultaneously denoted as VPVi *, wherein i=1,2,3...N；
Step 3, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PViThe N number of H bridge list obtained with step 2 The DC voltage instruction value V of memberPVi *, by direct current voltage regulator under current source mode, it is calculated under current source mode The active-power P of each H-bridge unitCi, wherein i=1,2,3...N, calculating formula are as follows:
Wherein, KCVPFor direct current voltage regulator proportionality coefficient, K under current source modeCVIFor DC voltage tune under current source mode Device integral coefficient is saved, i=1,2,3...N, s are Laplace operator；
Step 4, the active-power P of N number of H-bridge unit under the current source mode obtained according to step 3CiCurrent source mode is calculated Under N number of H-bridge unit the sum of active power and be denoted as PCT, calculating formula are as follows:
Step 5, to the filter capacitor voltage actual value V sampled in step 1oIt carries out locking phase and obtains grid voltage amplitude VmAnd phase θg；The filter capacitor voltage actual value V that will be sampled in step 1 by virtual synchronous rotating coordinate transformationoRotation is converted into sit Current source mode filter capacitor voltage active component V under mark systemCodWith current source mode filter capacitor voltage power-less component VCoq； The filter inductance current actual value I that will be sampled in step 1 by virtual synchronous rotating coordinate transformationLIt is converted into rotational coordinates Current source mode filter inductance active component of current I under systemCLdWith current source mode filter inductance reactive component of current ICLq；
Step 6, the sum of active power of N number of H-bridge unit P under the current source mode obtained according to step 4CTIt is obtained with step 5 Grid voltage amplitude VmFilter inductance active component of current reference value under current source mode is calculatedIts calculating formula are as follows:
Step 7, the current source mode filter inductance active component of current I obtained according to step 5CLd, current source mode filter inductance Reactive component of current ICLqFilter inductance active component of current reference value under the current source mode obtained with step 6Lead to respectively Reactive current adjuster under watt current adjuster and current source mode, is calculated under current source mode under overcurrent source module D axis PI regulated value ECdWith q axis PI regulated value E under current source modeCq, calculating formula is respectively as follows:
Wherein, KCiPFor current regulator proportionality coefficient, K under current source modeCiIIt is integrated for current regulator under current source mode Coefficient；
Step 8, d axis PI regulated value E under the current source mode obtained according to step 7Cd, q axis PI regulated value E under current source modeCq The current source mode filter capacitor voltage active component V obtained with step 5Cod, current source mode filter capacitor voltage power-less component VCoqAnti- coordinate transform is rotated by virtual synchronous obtain inverter under current source mode always modulate wave voltage VCr；
Step 9, the active-power P of N number of H-bridge unit under the current source mode obtained according to step 3CiThe electric current obtained with step 4 The sum of active power of N number of H-bridge unit P under source moduleCTThe power partition coefficient of each H-bridge unit under calculating current source module FactorCi, i=1,2,3...N, calculating formula are as follows:
Step 10, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, current source mould that step 8 obtains Inverter always modulates wave voltage V under formulaCrN number of H-bridge unit power partition coefficient under the current source mode obtained with step 9 FactorCi, the modulation wave voltage V of each H-bridge unit under calculating current source moduleCri, i=1,2,3...N, calculating formula are as follows:
Step 11, it before switching, latches filter inductance active component of current reference value under upper periodic current source module and is denoted as It latches N number of H-bridge unit power partition coefficient under upper periodic current source module and is denoted as FactorCmi, each voltage source is calculated Direct current voltage regulator feedforward control amount I under modeVFeedi, i=1,2,3...N, calculating formula are as follows:
Step 12, before switching, d axis PI regulated value E under the current source mode obtained according to step 7Cd, q axis PI under current source mode Regulated value ECqThe current source mode filter capacitor voltage active component V obtained with step 5CodCurrent source mode subinverse is calculated Become the amplitude V that device always modulates wave voltageCrmAnd phase thetaCr, calculating formula are as follows:
Step 13, the filter capacitor voltage actual value V that will be sampled in step 1oIt is converted by virtual synchronous rotating coordinate transformation At the voltage source mode filter capacitor voltage active component V under rotating coordinate systemVodWith voltage source mode filter capacitor voltage power-less Component VVoq；
Step 14, the power network current actual value I that will be sampled in step 1SIt is converted into revolving by virtual synchronous rotating coordinate transformation Turn the voltage source mode power network current active component I under coordinate systemVSdWith voltage source mode power network current reactive component IVSq；
Step 15, the voltage source mode filter capacitor voltage active component V obtained according to step 13Vod, voltage source mode filtered electrical Hold voltage power-less component VVoqThe voltage source mode power network current active component I obtained with step 14VSd, voltage source mode power grid electricity Flow reactive component IVSq, by calculating and filtering through low-pass first order filter, obtaining inverter output under voltage source mode averagely has Function power PVoWith average reactive power QVo, calculating formula are as follows:
Wherein, τ is low-pass first order filter time constant；
Step 16, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, N number of H bridge list that step 2 obtains The DC voltage instruction value V of memberPVi *Direct current voltage regulator feedforward control amount under the N number of voltage source mode obtained with step 11 IVFeedi, by direct current voltage regulator under voltage source mode, the wattful power of each H-bridge unit under voltage source mode is calculated Rate PVi, wherein i=1,2,3...N, calculating formula are as follows:
Wherein, KVVPFor direct current voltage regulator proportionality coefficient, K under voltage source modeVVIFor DC voltage tune under voltage source mode Section device integral coefficient, i=1,2,3...N；
Step 17, the active-power P of N number of H-bridge unit under the voltage source mode obtained according to step 16ViVoltage source mould is calculated The sum of active power of N number of H-bridge unit and P is denoted as under formulaVT, calculating formula are as follows:
Step 18, the sum of active power of N number of H-bridge unit P under the voltage source mode obtained according to step 17VTIt is obtained with step 15 Voltage source mode under inverter export average active power PVoVoltage is calculated through active power-frequency droop governing equation The output angular frequency of inverter under source moduleVo, angular frequency is exported under voltage source modeVoVoltage source mould is obtained by integral The output phase angle theta of inverter under formulaVo, active power-frequency droop governing equation are as follows:
ωVo=ω*+m(PVT-PVo)
Wherein ω*For synchronized angular frequency, m is active sagging coefficient；
Step 19, inverter exports average reactive power Q under the voltage source mode obtained according to step 15VoThrough reactive power-electricity It depresses the governing equation that hangs down and filter capacitor voltage active component reference value under voltage source mode is calculatedAnd voltage source mode Lower filter capacitor voltage power-less component reference valueIts sagging governing equation of reactive power-voltage are as follows:
Wherein E is with reference to electromotive force, and n is idle sagging coefficient, Q*Reactive power instruction is given for upper layer；
Step 20, inverter always modulates the amplitude V of wave voltage under the current source mode obtained according to step 12CrmAnd phase thetaCr, step The output phase angle theta of inverter under rapid 18 obtained voltage source modesVoAnd filter capacitor under the obtained voltage source mode of step 19 Voltage active component reference valueRespectively by Phase synchronization adjuster and amplitude synchronous governor under voltage source mode, calculate Inverter always modulates the amplitude V of wave voltage under voltage source mode when obtaining switchingVrmAnd phase thetaVr, calculating formula are as follows:
Wherein, KVSP1For amplitude synchronous governor proportionality coefficient, K under voltage source modeVSI1For the same step of amplitude under voltage source mode Save device integral coefficient, KVSP2For Phase synchronization adjuster proportionality coefficient, K under voltage source modeVSI2It is same for phase under voltage source mode Walk adjuster integral coefficient；
Step 21, the active-power P of N number of H-bridge unit under the voltage source mode obtained according to step 16ViThe electricity obtained with step 17 The sum of active power of N number of H-bridge unit P under source modeVTCalculate the power partition coefficient of each H-bridge unit under voltage source mode FactorVi, i=1,2,3...N, calculating formula are as follows:
Step 22, the DC voltage actual value V of the N number of H-bridge unit obtained according to step 1PVi, when the switching that step 20 obtains Inverter always modulates the amplitude V of wave voltage under voltage source modeVrmAnd phase thetaVrAnd N under the obtained voltage source mode of step 21 A H-bridge unit power partition coefficient FactorVi, the modulating wave of each H-bridge unit is electric under voltage source mode when switching is calculated Press VVri, i=1,2,3...N, calculating formula are as follows:
The voltage source mode seamless switching current source mode control method includes:
Firstly, start modulating wave voltage synchronous adjuster before switching, filter capacitor electricity under the voltage source mode that step 19 is obtained Press active component reference valueD axis PI regulated value under the upper periodic current source module that step 7 obtainsIt is obtained with step 5 The current source mode filter capacitor voltage active component V arrivedCodIt obtains switching preceding current source by modulating wave voltage synchronous adjuster Filter inductance active component of current reference value under modeIts calculating formula are as follows:
Wherein, KCSPFor current source mode modulated wave voltage synchronous governor proportionality coefficient, KCSIFor current source mode modulated Wave voltage synchronous governor integral coefficient；
Secondly, latching the filter inductance active component of current under upper periodic voltage source module after the completion of modulating wave voltage synchronous and joining Value is examined to be denoted asIt latches N number of H-bridge unit power partition coefficient under upper periodic voltage source module and is denoted as FactorVmi, calculate Obtain direct current voltage regulator feedforward control amount I under each current source modeCFeedi, i=1,2,3...N, calculating formula are as follows:
Finally, by direct current voltage regulator feedforward control amount I under current source modeCFeediIt is superimposed upon under each current source mode straight The output of current-voltage regulator, when switching is calculated under current source mode each H-bridge unit active-power PC′i, wherein i= 1,2,3...N, calculating formula are as follows:
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