CN112564535B - Control method of common direct current bus cascade H-bridge photovoltaic grid-connected inverter - Google Patents

Control method of common direct current bus cascade H-bridge photovoltaic grid-connected inverter Download PDF

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CN112564535B
CN112564535B CN202011472559.6A CN202011472559A CN112564535B CN 112564535 B CN112564535 B CN 112564535B CN 202011472559 A CN202011472559 A CN 202011472559A CN 112564535 B CN112564535 B CN 112564535B
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CN112564535A (en
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赵涛
陈道炼
冯之健
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Qingdao University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

Abstract

The invention discloses a control method of a common direct current bus cascaded H-bridge photovoltaic grid-connected inverter, belongs to the photovoltaic power generation technology in the field of electrical engineering, and aims to enable a three-phase common direct current bus cascaded H-bridge photovoltaic grid-connected inverter to still normally operate when the output power of a photovoltaic array is unbalanced. The method mainly comprises the following steps: controlling the voltage of the N public direct current buses; obtaining an active current instruction value according to the instruction value of the active power and carrying out no-static-difference control on the current of the power grid; distributing the modulation voltage of all the modules according to the active power transmitted by all the modules; the output voltage of all three-level full-bridge LLC converters is controlled. By adopting the method, the multi-path maximum power point tracking control of the photovoltaic array can be realized, the problem of interphase power imbalance is avoided, and the active power transmitted by the modules at the corresponding positions of the three-phase converter is the same. In addition, even if the output power of the photovoltaic array is different, the system can still normally operate.

Description

Control method of common direct current bus cascade H-bridge photovoltaic grid-connected inverter
Technical Field
The invention belongs to the photovoltaic power generation technology in the field of electrical engineering, and particularly relates to a control method of a common direct-current bus cascade H-bridge photovoltaic grid-connected inverter.
Background
Large-scale photovoltaic power generation systems are more commercially attractive than low-power photovoltaic power generation systems because they can further reduce the power generation cost per watt of the system, a trend that requires photovoltaic power generation systems with higher voltage and power levels at the point of common coupling. Therefore, the three-phase photovoltaic grid-connected inverter based on the cascaded H-bridge converter attracts attention of many scholars due to excellent performance. The modular structure of the inverter is easy to expand, the inverter can output higher voltage and power by using mainstream and common low-voltage switching devices in the market, and the inverter can be connected to a medium-voltage or even high-voltage power grid without using a power frequency transformer. In addition, the multi-level step wave output by the alternating current side allows the converter to work at a lower switching frequency, which helps to improve the conversion efficiency.
In all high-voltage high-power photovoltaic grid-connected inverters based on the cascade H-bridge topology, two kinds of topology researches are more: one is an independent direct current bus topology, and the other is a common direct current bus topology. The independent direct current bus topology means that the input ends of all modules are respectively connected with a photovoltaic array, and the common direct current bus topology means that the input ends of all three-phase modules are connected in parallel to form a common direct current bus, and then the photovoltaic array is connected to the common direct current bus. However, for an independent dc bus topology, each module is connected to a photovoltaic array individually, which can lead to intra-phase and inter-phase power imbalance problems because the output power of all photovoltaic arrays cannot be completely consistent. The in-phase power imbalance can cause over-modulation of modules with larger output power, and the inter-phase power imbalance can cause imbalance of output current of the three-phase inverter. Although the common direct-current bus topological structure does not have the problem of power imbalance between phases, the topological structure can only realize one path of maximum power point tracking control, and the power generation amount of the system can be reduced. In order to realize multi-path maximum power point tracking control, a plurality of Boost converters need to be connected to a common direct current bus, but the overall efficiency of the system is reduced. In view of the problems of the independent dc bus topology and the existing common dc bus topology, the documents "Xing Zhang, Mingda Wang, Tao Zhao, Wang Mao, Yuhua Hu, Renxian cao. polar company and Analysis of Medium-Voltage and High-Power Direct-linked PV inverter [ J ]. CES Transactions on Electrical machinery Systems and s, 2019, 3 (4): 327 & 334 (Xing Zhang, Mingda Wang, Tao Zhao, Wang Mao, Yuhua Hu, Renxian Cao, topology comparison and analysis of medium voltage high power direct-hanging type pv grid-connected inverter, CES motor and system declaration, volume 3, 4, pages 327 to 334 of 2019) introduces another common dc bus cascade H-bridge pv grid-connected inverter, specifically, a first module of phase a is connected in parallel with input ports of a first module of phase B and phase C to form a common dc bus, a second module of phase a is connected in parallel with input ports of a second module of phase B and phase C to form a common dc bus, and repeating the steps until the Nth module of the phase A and the input ports of the Nth modules of the phase B and the phase C are connected in parallel to form a common direct current bus (N is the number of modules contained in each phase of the three-phase converter), and then connecting a photovoltaic array on each common direct current bus. If a proper control strategy is adopted, the topological structure has no problem of interphase power imbalance, and can realize N-path maximum power tracking control, so that the comprehensive performance is relatively excellent.
Although the public direct-current bus cascade H-bridge photovoltaic grid-connected inverter does not have the problem of interphase power imbalance, the problem of power imbalance among modules in phases still exists. However, the documents "Xing Zhang, Mingda Wang, Tao Zhao, Wang Mao, Yuhua Hu, Renxian cao. polar company and Analysis of Medium-Voltage and High-Power Direct-linked PV inverter [ J ]. CES Transactions on electric Machines and Systems, 2019, 3 (4): 327- & ltx & gt 334 (Xing Zhang, Mingda Wang, Tao Zhao, Wang Mao, Yuhua Hu, Renxian Cao, topology comparison and analysis of medium-voltage high-power direct-hanging photovoltaic grid-connected inverter, CES motor and system declaration, volume 3, 4, pages 327 to 334 in 2019) & ltdoes not carry out detailed analysis on the problem of power imbalance among modules in the phase of the topological structure, nor does it propose a related control strategy to solve the problem.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the limitation of the scheme, and provide a control method of a common direct current bus cascaded H-bridge photovoltaic grid-connected inverter, which not only can realize multi-path maximum power point tracking control, but also can still normally operate a system when the output power of a photovoltaic array is unbalanced.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a control method of a common direct current bus cascade H bridge photovoltaic grid-connected inverter is disclosed, the cascade H bridge photovoltaic grid-connected inverter applying the control method is a three-phase photovoltaic grid-connected inverter and consists of an A phase, a B phase and a C phase; the phase A, the phase B and the phase C respectively comprise N modules, N is a positive integer greater than 1, and the structures of all the modules in the phase A, the phase B and the phase C are completely the same; all modules in the phase A, the phase B and the phase C are formed by connecting a three-level full-bridge LLC converter with an H-bridge converter in series; the input ports of the ith modules which are arranged in the A phase, the B phase and the C phase respectively and correspond to each other are connected in parallel to form a common direct current bus, i is 1, 2, so, N, for a cascade H-bridge photovoltaic grid-connected inverter comprising N modules in each phase, N common direct current buses are formed in total, and each common direct current bus is connected in parallel with a photovoltaic array; the alternating current output ends of all the modules in the phase A, the phase B and the phase C are connected in series to form three module strings, one ends of the three module strings are connected together to form a common point, and the other ends of the three module strings are respectively connected to a three-phase star-connected power grid through filter inductors;
the control method comprises the following steps of voltage control of N public direct current buses, power grid current control, modulation wave distribution of an H-bridge converter and output voltage control of a three-level full-bridge LLC converter, and comprises the following steps:
step 1, voltage control of N public direct current buses
Step 1.1, respectively sampling the voltage of N public direct current buses and the output current of the photovoltaic array connected in parallel on each public direct current bus to obtain voltage sampling values V of the N public direct current busesDiAnd corresponding output current sampling values I of N photovoltaic arraysDi，i＝1，2，…，N；
Step 1.2, obtaining voltage sampling values V of the N public direct current buses according to the step 1.1DiAnd output current sampling values I of N photovoltaic arraysDiRespectively carrying out maximum power point tracking control on the N photovoltaic arrays to obtain the maximum power point voltage of the N photovoltaic arrays
Figure BDA0002832888820000041
Step 1.3, using a second-order band elimination filter to carry out voltage sampling value V on the N public direct current buses obtained in the step 1.1DiFiltering to obtain voltage sampling values V of the N filtered public direct current busesDi_AThe calculation formula is as follows:
Figure BDA0002832888820000042
where s is the Laplace operator, Q is the quality factor of the filter, ω0Is the natural angular frequency of the filter;
step 1.4, obtaining the maximum power point voltage of the N photovoltaic arrays obtained in the step 1.2
Figure BDA0002832888820000043
As reference values of the voltages of the N public direct current buses, respectively filtering voltage sampling values V of the N public direct current buses by using N identical voltage regulatorsDi_AControl is carried out, the output of the N voltage regulators are respectively N reference current signals ICiThe calculation formula is as follows:
Figure BDA0002832888820000044
wherein, KVPIs the proportionality coefficient of the voltage regulator, KVIIs the integral coefficient of the voltage regulator;
step 1.5, voltage sampling values V of the N filtered public direct current busesDi_AAnd N reference current signals I obtained in step 1.4CiMultiplying to obtain the active power P output by N modulesMiThe calculation formula is as follows:
PMi＝VDi_AICi，i＝1，2，...，N
step 1.6, calculating the active power P output by the N modules according to the step 1.5MiCalculating to obtain the total active power transmitted from the direct current side to the alternating current side of the three-phase cascaded H-bridge photovoltaic grid-connected inverter and recording as the total active power PMTThe calculation formula is as follows:
Figure BDA0002832888820000045
step 2, power grid current control
In the step 2.1, the method comprises the following steps of,respectively sampling the three-phase power grid voltage and the three-phase power grid current to obtain a sampling value v of the three-phase power grid voltagegA，vgB，vgCAnd sampling values i of the three-phase network currentgA，igB，igC；
Step 2.2, using a digital phase-locked loop to obtain a sampling value v of the three-phase power grid voltage obtained in the step 2.1gA，vgB，vgCPerforming phase locking to obtain a phase angle ω t and an angular frequency ω of the grid voltage and an amplitude V of the grid phase voltageg(ii) a Converting the synchronous rotation coordinates to obtain the sampled value v of the three-phase network voltage in step 2.1gA，vgB，vgCConverting the voltage into the active component e of the network voltage under the rotating coordinate systemdAnd the reactive component e of the network voltageq(ii) a Converting the synchronous rotation coordinate into a sampling value i of the three-phase power grid current obtained in the step 2.1gA，igB，igCConverting the power into the active component i of the network current under the rotating coordinate systemdAnd reactive component i of the network currentq；
Active component e of the network voltagedAnd the reactive component e of the network voltageqThe calculation formula of (c) is:
Figure BDA0002832888820000051
active component i of the grid currentdAnd reactive component i of the network currentqThe calculation formula of (A) is as follows:
Figure BDA0002832888820000052
step 2.3, obtaining the total active power P according to the step 1.6MTAnd 2.2, obtaining the power grid phase voltage amplitude VgCalculating the active current reference value
Figure BDA0002832888820000053
The calculation formula is as follows:
Figure BDA0002832888820000054
step 2.4, sending out total reactive power Q according to the requirement of the photovoltaic inverterMTAnd 2.2, obtaining the voltage amplitude V of the power grid phasegCalculating a reactive current reference value
Figure BDA0002832888820000055
The calculation formula is as follows:
Figure BDA0002832888820000056
step 2.5, respectively using an active current regulator and a reactive current regulator to convert the active component i of the power grid currentdAnd reactive component i of the network currentqControl to active current reference value
Figure BDA0002832888820000061
And a reactive current reference value
Figure BDA0002832888820000062
And obtaining the output value delta v of the active current regulatordAnd the output value Deltav of the reactive current regulatorqThe calculation formula is respectively:
Figure BDA0002832888820000063
wherein, KiP1As the proportionality coefficient of the active current regulator, KiI1Is the integral coefficient of the active current regulator; kiP2Is the proportionality coefficient of the reactive current regulator, KiI2Is the integral coefficient of the reactive current regulator;
step 2.6, obtaining the active component e of the power grid voltage according to the step 2.2dReactive component e of the grid voltageqActive component i of the grid currentdReactive component of the grid current iqGrid voltage angular frequency omega, active current obtained in step 2.3 and step 2.4Reference value
Figure BDA0002832888820000064
And a reactive current reference value
Figure BDA0002832888820000065
And the output value Deltav of the active current regulator obtained in step 2.5dAnd the output value Deltav of the reactive current regulatorqObtaining the amplitude v of the active modulation voltagedAnd the amplitude v of the reactive modulation voltageqThe calculation formula is as follows:
Figure BDA0002832888820000066
wherein L isfIs a filter inductor;
step 2.7, the amplitude of the active modulation voltage obtained in the step 2.6 is usedvdAnd the amplitude v of the reactive modulation voltageqObtaining modulation voltage v of the three-phase cascade H-bridge photovoltaic grid-connected inverter under the natural coordinate system through synchronous rotation coordinate inverse transformationcA，vcB，vcCThe calculation formula is as follows:
Figure BDA0002832888820000067
step 3, distribution of modulation wave of H-bridge converter
Step 3.1, calculating the active power P output by the N modules according to the step 1.5MiAnd the total active power P calculated in step 1.6MTAnd calculating the modulation voltage distribution coefficients k of all the modules in the A phase, the B phase and the C phaseAi，kBi，kCiThe calculation formula is as follows:
Figure BDA0002832888820000071
step 3.2, obtaining the modulation voltage v of the three-phase cascade H-bridge photovoltaic grid-connected inverter according to the step 2.7cA，vcB，vcCAnd the modulation voltage distribution coefficients k of all the modules in the A phase, the B phase and the C phase obtained in the step 3.1Ai，kBi，kCiCalculating to obtain the modulation voltage v of all the modules in the A phase, the B phase and the C phaseAi，vBi，vCiThe calculation formula is as follows:
Figure BDA0002832888820000072
step 3.3, recording the modulation wave of any H-bridge converter in the A phase as mAiAnd the modulation wave of any H-bridge converter in the B phase is mBiAnd the modulation wave of any H-bridge converter in the C phase is mCiThen modulate the wave mAiModulated wave mBiAnd a modulation wave mCiIs calculated as follows:
Figure BDA0002832888820000073
wherein, VHAiIs the sampling value of the voltage of the DC bus capacitor of the ith A-phase H-bridge converter, VHBiIs the sampling value of the DC bus capacitor voltage of the ith B-phase H-bridge converter, VHCiSampling values of the DC bus capacitor voltage of the ith C-phase H-bridge converter;
step 4, controlling the output voltage of the three-level full-bridge LLC converter
Step 4.1, respectively carrying out voltage sampling values V on all direct-current bus capacitors of the A-phase H-bridge converter by using a second-order band elimination filterHAiDC bus capacitor voltage sampling value V of B-phase all-H-bridge converterHBiAnd all C-phase H-bridge converter DC bus capacitor voltage sampling value VHCiFiltering, and recording voltage sampling values of all the DC bus capacitors of the A-phase H-bridge converter as VHAi_AAnd the voltage sampling value of the DC bus capacitor of the B-phase all-H-bridge converter after filtering is recorded as VHBi_AAnd the voltage sampling value of the DC bus capacitor of the C-phase all-H-bridge converter after filtering is recorded as VHCi_AThe calculation formula is respectively:
Figure BDA0002832888820000081
Figure BDA0002832888820000082
Figure BDA0002832888820000083
step 4.2, using an LLC voltage controller to obtain voltage sampling values V of all the DC bus capacitors of the A-phase H-bridge converter after filtering obtained in the step 4.1HAi_AIs controlled to be VDi_A/NTUsing an LLC voltage controller to obtain filtered voltage sampling values V of all DC bus capacitors of the B-phase H-bridge converter obtained in the step 4.1HBi_AIs controlled to be VDi_A/NTUsing an LLC voltage controller to obtain voltage sampling values V of all DC bus capacitors of the C-phase and all H-bridge converter after filtering obtained in the step 4.1HCi_AIs controlled to be VDi_A/NTObtaining the switching frequency f of all three-level full-bridge LLC converters of the A phaseAiSwitching frequency f of all three-level full-bridge LLC converter in B phaseBiSwitching frequency f of all three-level full-bridge LLC converter in C phaseCiThe calculation formula is as follows:
Figure BDA0002832888820000084
Figure BDA0002832888820000085
Figure BDA0002832888820000086
wherein N isTIs a high-frequency transformer in a three-level full-bridge LLC converterTurn ratio of primary side to secondary side, KDPIs the proportionality coefficient, K, of the LLC voltage controllerDIIs the integral coefficient of the LLC voltage controller.
Compared with the prior art, the invention has the beneficial effects that:
1. the tracking control of multiple maximum power points of the photovoltaic array can be realized, the problem of interphase power imbalance is avoided, and the active power transmitted by the modules at the corresponding positions of the three-phase converter is the same;
2. even if the output power of the photovoltaic array is different, the system can still normally operate.
Drawings
Fig. 1 is a topological structure of a common dc bus cascade H-bridge photovoltaic grid-connected inverter implemented by the present invention.
Fig. 2 is a circuit configuration diagram of a first module of a phase a of the common dc bus cascade H-bridge photovoltaic grid-connected inverter according to the embodiment of the present invention.
Fig. 3 is a block diagram of a control strategy of a common dc bus cascade H-bridge photovoltaic grid-connected inverter implemented by the present invention.
Fig. 4 is a flowchart of a control strategy of a common dc bus cascade H-bridge photovoltaic grid-connected inverter implemented in the present invention.
Fig. 5 is a schematic diagram of modulation wave distribution of all H-bridge converters in the a-phase, B-phase, and C-phase implemented in the present invention.
Fig. 6 is a schematic diagram of an output waveform of a carrier phase-shifted sine wave pulse width modulation strategy implemented by the invention, in which the phase a includes two modules.
Fig. 7 is a schematic diagram of the driving waveforms of the switching devices of the LLC converter in the first module of phase a when the frequency conversion modulation strategy of the three-level full-bridge LLC converter implemented by the present invention is adopted.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further clearly and completely described below with reference to the accompanying drawings and embodiments.
Fig. 1 is a topological structure of a common dc bus cascade H-bridge photovoltaic grid-connected inverter implemented by the present invention, and the topology structure is composed of an a phase, a B phase and a C phase. The phase A comprises N modules, the phase B comprises N modules, the phase C comprises N modules, N is a positive integer larger than 1, and the structures of all the modules in the phase A, the phase B and the phase C are completely the same. All modules in the A phase, the B phase and the C phase are composed of a three-level full-bridge LLC converter connected with an H-bridge converter in series. The input ports of the ith modules which are arranged in the phase A, the phase B and the phase C respectively and correspond to each other are connected in parallel to form a common direct current bus, and i is 1, 2. Specifically, the first module of the phase A and the input ports of the first modules of the phase B and the phase C are connected in parallel to form a common direct current bus, the second module of the phase A and the input ports of the second modules of the phase B and the phase C are connected in parallel to form a common direct current bus, and the like, until the nth module of the phase A and the input ports of the nth modules of the phase B and the phase C are connected in parallel to form a common direct current bus. For a cascade H-bridge photovoltaic grid-connected inverter with each phase comprising N modules, N public direct current buses are formed in total, and each public direct current bus is connected with a photovoltaic array in parallel; the alternating current output ends of all the modules in the phase A, the phase B and the phase C are connected in series to form three module strings, one ends of the three module strings are connected together to form a common point N2, and the other ends of the three module strings are respectively connected to a three-phase star-connected power grid through filter inductors.
In FIG. 1, vgA、vgBAnd vgCRepresenting the phase voltages, i, of a three-phase networkgA、igBAnd igCRespectively represents the phase current of a three-phase power grid, and is the output current L of the common direct current bus cascade H-bridge photovoltaic grid-connected inverter implemented by the inventionfRepresenting the filter inductance. CHAiDC bus capacitance, C, of an H-bridge converter representing the ith module of phase AHBiDC bus capacitance of H-bridge converter representing the ith module of phase B, CHCiThe dc bus capacitance i-1, 2.., N of the H-bridge converter of the i-th module in C-phase is represented. VHAiSample value, V, of DC bus capacitor voltage of H-bridge converter representing No. i module of A phaseHBiSample value of DC bus capacitor voltage of H-bridge converter representing B-phase i-th module, VHCiThe sampling values of the dc-side capacitor voltage of the H-bridge converter of the C-phase i-th module are represented, i being 1, 2. CDiIs shown asI direct current bus capacitors of the photovoltaic array, IDiSample value, V, representing the output current of the ith photovoltaic arrayDiThe voltage sampling value of the ith common direct current bus is represented, i is 1, 2.
Fig. 2 is a circuit configuration diagram of a first module of a phase a of the common dc bus cascade H-bridge photovoltaic grid-connected inverter according to the embodiment of the present invention. Main switch tube QA11～QA14(including anti-parallel diode and equivalent capacitor), voltage dividing capacitor CdA11And CdA12Freewheel diode DA11And DA12And a flying capacitor CSA11Forming a left bridge arm of the three-level LLC; qA15～QA18(including anti-parallel diode and equivalent capacitor), voltage-dividing capacitor CdA11And CdA12Freewheel diode DA13And DA14And a flying capacitor CsA12Forming the right arm of the three-level LLC. L isrA1、CrA1And LmA1Respectively representing a resonant inductor, a resonant capacitor and an excitation inductor of the LLC converter; t isrA1Representing a transformer, the number of turns of the primary winding being N of the number of turns of the secondary windingTAnd (4) multiplying. DRA11～DRA14Representing output rectifier diodes, H-bridge converters from TA11～TA14Composition C ofHA1Representing the DC bus capacitance, V, of the H-bridge converterHA1And the sampling value represents the DC bus capacitor voltage of the H-bridge converter.
FIG. 3 is a block diagram of a common DC bus cascaded H-bridge photovoltaic grid-connected inverter control strategy implemented in the present invention, which includes using a digital phase-locked loop to match the grid voltage (v)gA，vgBAnd vgC) Phase locking and supply voltage (v)gA，vgBAnd vgC) And the grid current (i)gA，igBAnd igC) Performing synchronous rotating coordinate conversion (i.e. converting from a natural coordinate system to a synchronous rotating coordinate system, abc/dq), voltage control of N public direct current buses, power grid current control, distribution of modulation waves of an H-bridge converter, output voltage control of an A-phase three-level full-bridge LLC converter, output voltage control of a B-phase three-level full-bridge LLC converter and output voltage control of a C-phase three-level full-bridge LLC converter. Fig. 4 is a flowchart of a control strategy of a common dc bus cascade H-bridge photovoltaic grid-connected inverter implemented in the present invention.
Referring to fig. 1, 2, 3 and 4, the implementation of the present invention is as follows:
step 1, voltage control of N public direct current buses
Step 1.1, respectively sampling the voltages of N public direct current buses and the output current of the photovoltaic array connected in parallel on each public direct current bus to obtain voltage sampling values V of the N public direct current busesDiAnd corresponding output current sampling values I of N photovoltaic arraysDi，i＝1，2，…，N。
In this embodiment, in order to omit direct connection of the power frequency isolation type transformer to the 35kV medium voltage power grid, the number N of modules of the three phases should be designed to be between 32 and 40.
Step 1.2, obtaining voltage sampling values V of the N public direct current buses according to the step 1.1DiAnd output current sampling values I of N photovoltaic arraysDiRespectively carrying out maximum power point tracking control on the N photovoltaic arrays to obtain maximum power point voltages of the N photovoltaic arrays
Figure BDA0002832888820000111
Step 1.3, using a second-order band elimination filter to carry out voltage sampling value V on the N public direct current buses obtained in the step 1.1DiFiltering to obtain voltage sampling values V of the N filtered public direct current busesDi_AThe calculation formula is as follows:
Figure BDA0002832888820000121
where s is the Laplace operator, Q is the quality factor of the filter, ω0Is the natural angular frequency of the filter. In this embodiment, ω0628rad/s, and Q0.707. So ω of0628rad/s because when the frequency of the three-phase mains voltage is 50Hz, 100Hz voltage fluctuations occur on the input bus capacitance of all three-level full-bridge LLC converters. Due to the fact thatHere, the second-order band-stop filter is mainly used for filtering out 100Hz voltage ripple on a dc bus capacitor of the three-level full-bridge LLC converter.
Step 1.4, obtaining the maximum power point voltage of the N photovoltaic arrays obtained in the step 1.2
Figure BDA0002832888820000122
As reference values of the voltages of the N public direct current buses, respectively filtering voltage sampling values V of the N public direct current buses by using N identical voltage regulatorsDi_AControl is carried out, the output of the N voltage regulators are respectively N reference current signals ICiThe calculation formula is as follows:
Figure BDA0002832888820000123
wherein, KVPIs the proportionality coefficient of the voltage regulator, KVIIs the integral coefficient of the voltage regulator. In this example, KVP＝5，KVI250. By filtering voltage sampling values V of N common direct current busesDi_AControlling maximum power point voltage to N photovoltaic arrays
Figure BDA0002832888820000124
The output power of the photovoltaic array can be obtained to the maximum extent.
Step 1.5, voltage sampling values V of the N filtered public direct current busesDi_AAnd N reference current signals I obtained in step 1.4CiMultiplying to obtain the active power P output by N modulesMiThe calculation formula is as follows:
PMi＝VDi_AICi，i＝1，2，...，N
step 1.6, calculating the active power P output by the N modules according to the step 1.5MiCalculating to obtain the total active power transmitted from the direct current side to the alternating current side of the three-phase cascaded H-bridge photovoltaic grid-connected inverter and recording as the total active power PMTThe calculation formula is as follows:
Figure BDA0002832888820000131
step 2, power grid current control
Step 2.1, respectively sampling the three-phase power grid voltage and the three-phase power grid current to obtain a sampling value v of the three-phase power grid voltagegA，vgB，vgCAnd sampling values i of the three-phase network currentgA，igB，igC。
Step 2.2, using a digital phase-locked loop to obtain a sampling value v of the three-phase power grid voltage obtained in the step 2.1gA，vgB，vgCPerforming phase locking to obtain a phase angle omega t and an angular frequency omega of the power grid voltage and an amplitude V of the power grid phase voltageg(ii) a Converting the synchronous rotation coordinates to obtain the sampled value v of the three-phase network voltage in step 2.1gA，vgB，vgCConverting the voltage into the active component e of the network voltage under the rotating coordinate systemdAnd the reactive component e of the network voltageq(ii) a Converting the synchronous rotation coordinate into a sampling value i of the three-phase power grid current obtained in the step 2.1gA，igB，igCConverting the power grid current into a power grid current active component i under a rotating coordinate systemdAnd reactive component i of the network currentq。
Active component e of the network voltagedAnd the reactive component e of the network voltageqThe calculation formula of (A) is as follows:
Figure BDA0002832888820000132
active component i of the grid currentdAnd reactive component i of the network currentqThe calculation formula of (A) is as follows:
Figure BDA0002832888820000133
generally, there are many methods for obtaining a phase angle of a three-phase grid voltage, but there are two common methods in a photovoltaic grid-connected power generation occasion, which are a decoupling double-synchronous reference coordinate system phase-locked loop and a double-second order generalized integrator phase-locked loop, and the two methods correspond to the implementation of a grid-connected power converter synchronization and a static controller respectively. The basic variable detected by the phase-locked loop of the decoupling double-synchronous reference coordinate system is a phase angle, and the basic variable detected by the phase-locked loop of the double-second-order generalized integrator is a power grid frequency. The frequency of the power grid is more stable than the phase angle of the power grid, so that under the transient fault, the double-second-order generalized integrator phase-locked loop has smoother correspondence than a double-synchronous reference coordinate system phase-locked loop.
Step 2.3, obtaining the total active power P according to the step 1.6MTAnd 2.2, obtaining the voltage amplitude V of the power grid phasegCalculating the active current reference value
Figure BDA0002832888820000141
The calculation formula is as follows:
Figure BDA0002832888820000142
step 2.4, generating total reactive power Q according to the requirement of the photovoltaic inverterMTAnd 2.2, obtaining the voltage amplitude V of the power grid phasegCalculating a reactive current reference value
Figure BDA0002832888820000143
The calculation formula is as follows:
Figure BDA0002832888820000144
step 2.5, respectively using an active current regulator and a reactive current regulator to convert the active component i of the power grid currentdAnd reactive component i of the network currentqControl to active current reference value
Figure BDA0002832888820000145
And a reactive current reference value
Figure BDA0002832888820000146
And obtaining the output value delta v of the active current regulatordAnd the output value Deltav of the reactive current regulatorqThe calculation formula is respectively:
Figure BDA0002832888820000147
wherein, KiP1As the proportionality coefficient of the active current regulator, KinIs the integral coefficient of the active current regulator; kiP2Is the proportionality coefficient of the reactive current regulator, KiI2Is the integral coefficient of the reactive current regulator; in this example, KiP1＝1.8，KiI1＝200，KiP2＝1.8，KiI2＝200。
Step 2.6, obtaining the active component e of the power grid voltage according to the step 2.2dReactive component e of the grid voltageqActive component i of the grid currentdReactive component of the grid current iqGrid voltage angular frequency omega, active current reference value obtained in step 2.3 and step 2.4
Figure BDA0002832888820000148
And a reactive current reference value
Figure BDA0002832888820000149
And the output value Deltav of the active current regulator obtained in step 2.5dAnd the output value Deltav of the reactive current regulatorqObtaining the amplitude v of the active modulation voltagedAnd the amplitude v of the reactive modulation voltageqThe calculation formula is as follows:
Figure BDA0002832888820000151
wherein L isfIs a filter inductor;
step 2.7, the amplitude v of the active modulation voltage obtained in the step 2.6 is useddAnd the amplitude v of the reactive modulation voltageqThree-phase cascade H-bridge light under a natural coordinate system is obtained through synchronous rotation coordinate inverse transformationModulation voltage v of grid-connected invertercA，vcB，vcCThe calculation formula is as follows:
Figure BDA0002832888820000152
step 3, distribution of modulation wave of H-bridge converter
Step 3, distribution of modulation wave of H-bridge converter
Step 3.1, calculating the active power P output by the N modules according to the step 1.5MiAnd the total active power P calculated in step 1.6MTCalculating the modulation voltage distribution coefficient k of all modules in the A phase, the B phase and the C phaseAi，kBi，kCiThe calculation formula is as follows:
Figure BDA0002832888820000153
step 3.2, obtaining the modulation voltage v of the three-phase cascade H-bridge photovoltaic grid-connected inverter according to the step 2.7cA，vcB，vcCAnd the modulation voltage distribution coefficients k of all the modules in the A phase, the B phase and the C phase obtained in the step 3.1Ai，kBi，kCiCalculating to obtain the modulation voltage v of all the modules in the A phase, the B phase and the C phaseAi，vBi，vCiThe calculation formula is as follows:
Figure BDA0002832888820000154
in this embodiment, the modulation voltage of each module is distributed according to the proportion of the active power transmitted by each module, as shown in fig. 5. This is because the current output by all modules in the same phase is the same (the grid current for that phase), and therefore the output power of each module is proportional to the output voltage.
Step 3.3, recording the modulation wave of any H-bridge converter in the A phase as mAiOf H-bridge converters in phase BModulated wave is mBiAnd the modulation wave of any one H-bridge converter in the C phase is mCiThen modulate the wave mAiModulated wave mBiAnd a modulation wave mCiIs calculated as follows:
Figure BDA0002832888820000161
wherein, VHAiIs the sampling value of the voltage of the DC bus capacitor of the ith A-phase H-bridge converter, VHBiIs the sampling value of the DC bus capacitor voltage of the ith B-phase H-bridge converter, VHCiAnd sampling values of the direct-current bus capacitor voltage of the ith C-phase H-bridge converter.
After the modulation waves of all the H-bridge converters are calculated, the switch driving signals of all the H-bridge converters can be obtained by adopting a carrier phase-shifting sine wave pulse width modulation strategy. The carrier phase-shift sine wave pulse width modulation strategy refers to a carrier phase-shift sine wave pulse width modulation strategy commonly applied by a cascaded H-bridge converter, and is a more and mature technology used in the cascaded H-bridge converter. The pulse width modulation of the carrier phase-shifted sine wave is described in detail in the literature, for example, pages 84 to 88 of the monograph "high performance cascaded multilevel converter principle and application" published by mechanical industry publishers in kyoto and chen asia 2013. FIG. 6 is a schematic diagram of an output waveform of a carrier phase-shifted sine wave pulse width modulation strategy implemented by the present invention with phase A comprising two modules, where m isA1And mA2Representing modulated waves, v, of first and second A-phase H-bridge converters, respectivelyc1And vc2Representing the carriers of the A-phase first and second H-bridge converters, vHO1And vHO2Representing the AC output voltages, v, of the A-phase first and second H-bridge converters, respectivelyHATRepresenting the total voltage output by the a-phase converter. As can be seen from the figure, vc2Phase angle of (c) compared to vc1The lag is pi/2, i.e., there is a phase shift between the carriers. v. ofHO1And vHO2Are all three-level waveforms, and vHATIs a five-level step wave. Pulse width modulation strategy for phase-shifted sine wave based on carrierFor a converter with N H-bridge modules, the phase difference between the carriers of each module is pi/N. Fig. 6 illustrates the pulse width modulation of a carrier phase-shifted sine wave using two H-bridge modules as an example, so that the phase difference between the carriers is pi/2.
Step 4, controlling the output voltage of the three-level full-bridge LLC converter
Step 4.1, respectively carrying out voltage sampling values V on all direct-current bus capacitors of the A-phase H-bridge converter by using a second-order band elimination filterHAiDC bus capacitor voltage sampling value V of B-phase all-H-bridge converterHBiAnd all C-phase H-bridge converter DC bus capacitor voltage sampling value VHCiFiltering, and recording voltage sampling values of all the DC bus capacitors of the A-phase H-bridge converter as VHAi_AAnd the voltage sampling value of the DC bus capacitor of the B-phase all-H-bridge converter after filtering is recorded as VHBi_AAnd the voltage sampling value of the DC bus capacitor of the C-phase all-H-bridge converter after filtering is recorded as VHCi_AThe calculation formula is respectively:
Figure BDA0002832888820000171
Figure BDA0002832888820000172
Figure BDA0002832888820000173
in this embodiment, ω0628rad/s, and Q0.707. As mentioned above, the filtering process is to filter out the 100Hz voltage ripple on the dc bus capacitor of the H-bridge converter.
Step 4.2, using an LLC voltage controller to obtain voltage sampling values V of all the DC bus capacitors of the A-phase H-bridge converter after filtering obtained in the step 4.1HAi_AIs controlled to be VDi_A/NTSampling all the filtered DC bus capacitor voltages of the B-phase H-bridge converter obtained in the step 4.1 by using an LLC voltage controllerValue VHBi_AIs controlled to be VDi_A/NTUsing an LLC voltage controller to obtain voltage sampling values V of all filtered DC bus capacitors of the C-phase H-bridge converter obtained in the step 4.1HCi_AIs controlled to be VDi_A/NTObtaining the switching frequency f of all three-level full-bridge LLC converters of the A phaseAiSwitching frequency f of all three-level full-bridge LLC converter in B phaseBiSwitching frequency f of all three-level full-bridge LLC converter in C phaseCiThe calculation formula is as follows:
Figure BDA0002832888820000174
Figure BDA0002832888820000181
Figure BDA0002832888820000182
wherein, NTIs the turn ratio, K, of the primary side and the secondary side of a high-frequency transformer in a three-level full-bridge LLC converterDPIs the proportionality coefficient, K, of the LLC voltage controllerDIIs the integral coefficient of the LLC voltage controller.
In this example, KDP＝50，KDI10000. The strategy of frequency conversion modulation for three-level full-bridge LLC converters is described in detail in the literature, such as W.Chen, Y.Gu, and Z.Lu, "A novel three-level full-bridge converter inverter dc-dc converter inverter capable for high Power wide input applications," in APEC 07-two-connected Integrated IEEE Applied Power Electronics reference and expansion, Anaheim, CA, USA, Feb.25-Mar.1, 2007 (W.Chen, Y.Gu, and Z.Lu, a new three-level full-bridge resonant dc-dc converter suitable for high Power wide range input, APEC07, the Twenty-Second IEEE Applied Power electronic Conference and Boehu, 2007, 2.yearly). FIG. 7 shows the first mode of the A phase in the frequency conversion modulation strategy of a three-level full-bridge LLC converter implemented by the inventionA schematic diagram of the switching device drive waveforms of the LLC converters in the block. It can be seen that 1/f is present in each switching cycleA1Internal and external switch tube Q11And Q18Compared with an inner switch tube Q12And Q17Late turn on TO1Time, early turn off TF1Time; external switch tube Q14And Q14Compared with an inner switch tube Q13And Q16Late turn on TO1Time, early turn off TF1Time of day.

Claims (1)

1. A control method of a common direct current bus cascade H bridge photovoltaic grid-connected inverter is disclosed, the cascade H bridge photovoltaic grid-connected inverter applying the control method is a three-phase photovoltaic grid-connected inverter and consists of an A phase, a B phase and a C phase; the phase A, the phase B and the phase C respectively comprise N modules, N is a positive integer greater than 1, and the structures of all the modules in the phase A, the phase B and the phase C are completely the same; all modules in the phase A, the phase B and the phase C are formed by connecting a three-level full-bridge LLC converter with an H-bridge converter in series; the input ports of ith modules which are respectively arranged in the phase A, the phase B and the phase C and correspond to each other are connected in parallel to form a common direct current bus, i is 1, 2, N, for a cascade H-bridge photovoltaic grid-connected inverter which comprises N modules in each phase, N common direct current buses are formed in total, and each common direct current bus is connected in parallel with a photovoltaic array; the alternating current output ends of all the modules in the phase A, the phase B and the phase C are connected in series to form three module strings, one ends of the three module strings are connected together to form a common point, and the other ends of the three module strings are respectively connected to a three-phase star-connected power grid through filter inductors;
the control method is characterized by comprising the following steps of voltage control of N public direct-current buses, power grid current control, distribution of modulation waves of an H-bridge converter and output voltage control of a three-level full-bridge LLC converter:
step 1, voltage control of N public direct current buses
Step 1.1, respectively sampling the voltage of N public direct current buses and the output current of the photovoltaic array connected in parallel on each public direct current bus to obtain voltage sampling values of the N public direct current busesVDiAnd corresponding output current sampling values I of N photovoltaic arraysDi，i＝1，2，…，N；
Step 1.2, obtaining voltage sampling values V of the N public direct current buses according to the step 1.1DiAnd output current sampling values I of N photovoltaic arraysDiRespectively carrying out maximum power point tracking control on the N photovoltaic arrays to obtain maximum power point voltages of the N photovoltaic arrays
Figure FDA0002832888810000011
Step 1.3, using a second-order band elimination filter to carry out voltage sampling value V on the N public direct current buses obtained in the step 1.1DiFiltering to obtain voltage sampling values V of N filtered public direct-current busesDi_AThe calculation formula is as follows:
Figure FDA0002832888810000021
where s is the Laplace operator, Q is the quality factor of the filter, ω0Is the natural angular frequency of the filter;
step 1.4, obtaining the maximum power point voltage of the N photovoltaic arrays obtained in the step 1.2
Figure FDA0002832888810000022
As reference values of the voltages of the N public direct current buses, respectively filtering voltage sampling values V of the N public direct current buses by using N identical voltage regulatorsDi_AControl is carried out, the output of the N voltage regulators are respectively N reference current signals ICiThe calculation formula is as follows:
Figure FDA0002832888810000023
wherein, KVPIs the proportionality coefficient of the voltage regulator, KVIIs the integral coefficient of the voltage regulator;
step 1.5, voltage sampling values V of the N filtered public direct current busesDi_AAnd N reference current signals I obtained in step 1.4CiMultiplying to obtain the active power P output by N modulesMiThe calculation formula is as follows:
PMi＝VDi_AICi，i＝1，2，...，N
step 1.6, calculating the active power P output by the N modules according to the step 1.5MiCalculating to obtain the total active power transmitted from the direct current side to the alternating current side of the three-phase cascaded H-bridge photovoltaic grid-connected inverter and recording as the total active power PMTThe calculation formula is as follows:
Figure FDA0002832888810000024
step 2, power grid current control
Step 2.1, respectively sampling the three-phase power grid voltage and the three-phase power grid current to obtain a sampling value v of the three-phase power grid voltagegA，vgB，vgCAnd sampling values i of the three-phase network currentgA，igB，igC；
Step 2.2, the sampling value v of the three-phase power grid voltage obtained in the step 2.1 is subjected to digital phase-locked loopgA，vgB，vgCPerforming phase locking to obtain a phase angle omega t and an angular frequency omega of the power grid voltage and an amplitude V of the power grid phase voltageg(ii) a Converting the synchronous rotation coordinates to obtain the sampled value v of the three-phase network voltage in step 2.1gA，vgB，vgCConverting the voltage into the active component e of the network voltage under the rotating coordinate systemdAnd reactive component e of the network voltageq(ii) a Converting the synchronous rotation coordinate into a sampling value i of the three-phase power grid current obtained in the step 2.1gA，igB，igCConverting the power into the active component i of the network current under the rotating coordinate systemdAnd reactive component i of the network currentq；
Active component e of the network voltagedAnd the reactive component e of the network voltageqThe calculation formula of (c) is:
Figure FDA0002832888810000031
active component i of the grid currentdAnd reactive component i of the network currentqThe calculation formula of (A) is as follows:
Figure FDA0002832888810000032
step 2.3, obtaining the total active power P according to the step 1.6MTAnd 2.2, obtaining the voltage amplitude V of the power grid phasegCalculating the active current reference value
Figure FDA0002832888810000033
The calculation formula is as follows:
Figure FDA0002832888810000034
step 2.4, sending out total reactive power Q according to the requirement of the photovoltaic inverterMTAnd 2.2, obtaining the voltage amplitude V of the power grid phasegCalculating a reactive current reference value
Figure FDA0002832888810000035
The calculation formula is as follows:
Figure FDA0002832888810000036
step 2.5, respectively using an active current regulator and a reactive current regulator to convert the active component i of the power grid currentdAnd reactive component i of the network currentqControl to active current reference value
Figure FDA0002832888810000037
And a reactive current reference value
Figure FDA0002832888810000038
And obtaining the output value delta v of the active current regulatordAnd the output value Deltav of the reactive current regulatorqThe calculation formula is respectively:
Figure FDA0002832888810000041
wherein, KiP1As the proportionality coefficient of the active current regulator, KiI1Is the integral coefficient of the active current regulator; kiP2Is the proportionality coefficient of the reactive current regulator, KiI2Is the integral coefficient of the reactive current regulator;
step 2.6, obtaining the active component e of the power grid voltage according to the step 2.2dReactive component e of the grid voltageqActive component i of the grid currentdReactive component of the grid current iqGrid voltage angular frequency omega, active current reference value obtained in step 2.3 and step 2.4
Figure FDA0002832888810000042
And a reactive current reference value
Figure FDA0002832888810000043
And the output value Deltav of the active current regulator obtained in step 2.5dAnd the output value Deltav of the reactive current regulatorqObtaining the amplitude v of the active modulation voltagedAnd the amplitude v of the reactive modulation voltageqThe calculation formula is as follows:
Figure FDA0002832888810000044
wherein L isfIs a filter inductor;
step 2.7, the amplitude v of the active modulation voltage obtained in the step 2.6 is useddAnd the amplitude v of the reactive modulation voltageqObtaining modulation voltage v of the three-phase cascade H-bridge photovoltaic grid-connected inverter under the natural coordinate system through synchronous rotation coordinate inverse transformationcA，vcB，vcCThe calculation formula is as follows:
Figure FDA0002832888810000045
step 3, distribution of modulation wave of H-bridge converter
Step 3.1, calculating the active power P output by the N modules according to the step 1.5MiAnd the total active power P calculated in step 1.6MTAnd calculating the modulation voltage distribution coefficients k of all the modules in the A phase, the B phase and the C phaseAi，kBi，kCiThe calculation formula is as follows:
Figure FDA0002832888810000051
step 3.2, obtaining the modulation voltage v of the three-phase cascade H-bridge photovoltaic grid-connected inverter according to the step 2.7cA，vcB，vcCAnd the modulation voltage distribution coefficients k of all the modules in the A phase, the B phase and the C phase obtained in the step 3.1Ai，kBi，kCiCalculating to obtain the modulation voltage v of all the modules in the A phase, the B phase and the C phaseAi，vBi，vCiThe calculation formula is as follows:
Figure FDA0002832888810000052
step 3.3, recording the modulation wave of any H-bridge converter in the A phase as mAiAnd the modulation wave of any H-bridge converter in the B phase is mBiAnd the modulation wave of any one H-bridge converter in the C phase is mCiThen modulate the wave mAiModulated wave mBiAnd a modulation wave mCiIs calculated as follows:
Figure FDA0002832888810000053
wherein, VHAiIs the sampling value of the voltage of the DC bus capacitor of the ith A-phase H-bridge converter, VHBiIs the sampling value of the DC bus capacitor voltage of the ith B-phase H-bridge converter, VHCiSampling values of the DC bus capacitor voltage of the ith C-phase H-bridge converter;
step 4, controlling the output voltage of the three-level full-bridge LLC converter
Step 4.1, respectively carrying out voltage sampling values V on all direct-current bus capacitors of the A-phase H-bridge converter by using a second-order band elimination filterHAiDC bus capacitor voltage sampling value V of B-phase all-H-bridge converterHBiAnd all C-phase H-bridge converter DC bus capacitor voltage sampling value VHCiFiltering, and marking voltage sampling values of all the DC bus capacitors of the A-phase H-bridge converter as VHAi_AAnd the voltage sampling value of the DC bus capacitor of the B-phase all-H-bridge converter after filtering is recorded as VHBi_AAnd the voltage sampling value of the DC bus capacitor of the C-phase all-H-bridge converter after filtering is recorded as VHCi_AThe calculation formula is respectively:
Figure FDA0002832888810000061
Figure FDA0002832888810000062
Figure FDA0002832888810000063
step 4.2, using an LLC voltage controller to obtain voltage sampling values V of all the DC bus capacitors of the A-phase H-bridge converter after filtering obtained in the step 4.1HAi_AIs controlled to be VDi_A/NTUsing LLC voltage controller to filter all B-phase H-bridges obtained in step 4.1Converter direct current bus capacitor voltage sampling value VHBi_AIs controlled to be VDi_A/NTUsing an LLC voltage controller to obtain voltage sampling values V of all DC bus capacitors of the C-phase and all H-bridge converter after filtering obtained in the step 4.1HCi_AIs controlled to be VDi_A/NTObtaining the switching frequency f of all three-level full-bridge LLC converters of the A phaseAiSwitching frequency f of all three-level full-bridge LLC converter in B phaseBiSwitching frequency f of all three-level full-bridge LLC converter in C phaseCiThe calculation formula is as follows:
Figure FDA0002832888810000064
Figure FDA0002832888810000065
Figure FDA0002832888810000066
wherein N isTIs the turn ratio, K, of the primary side and the secondary side of a high-frequency transformer in a three-level full-bridge LLC converterDPIs the proportionality coefficient, K, of the LLC voltage controllerDIIs the integral coefficient of the LLC voltage controller.
CN202011472559.6A 2020-12-14 2020-12-14 Control method of common direct current bus cascade H-bridge photovoltaic grid-connected inverter Active CN112564535B (en)

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