CN112564172A - Control method of single-phase cascade photovoltaic grid-connected inverter - Google Patents

Control method of single-phase cascade photovoltaic grid-connected inverter Download PDF

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CN112564172A
CN112564172A CN202011472560.9A CN202011472560A CN112564172A CN 112564172 A CN112564172 A CN 112564172A CN 202011472560 A CN202011472560 A CN 202011472560A CN 112564172 A CN112564172 A CN 112564172A
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CN112564172B (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
    • 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
    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • 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
    • 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
    • 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
    • Y02E40/40—Arrangements for reducing harmonics

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  • Power Engineering (AREA)
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Abstract

The invention discloses a control method of a single-phase cascade type photovoltaic grid-connected inverter, and belongs to the field of photovoltaic power generation. The method is used for dealing with the working scene of serious unbalance of the output power of the photovoltaic module, and compared with the existing single-phase cascade H-bridge photovoltaic grid-connected inverter, the method can enlarge the operation range of the system to a greater extent. The method comprises the following steps: controlling the average value of the DC bus capacitor voltage of the H-bridge converter; controlling the grid-connected current; using modified nearest level approximation modulation; the control method comprises the steps of controlling a single-phase active filter and controlling the input direct-current bus voltage of a four-switch tube Buck-Boost converter. By adopting the method, even in a working scene with seriously unbalanced output power of the photovoltaic components, all the photovoltaic components can still work at the self maximum power point, and the power generation capacity of the system is maximized.

Description

Control method of single-phase cascade 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 single-phase cascade type photovoltaic grid-connected inverter.
Background
In 2017, new standards are set by the national electrical code of the united states, and the photovoltaic facilities on all buildings are required to have the capability of realizing the rapid turn-off of the component level in an emergency, which inevitably promotes the rapid development and wide application of the component level power electronic technology. Because each Power unit of the single-phase Cascaded H-bridge (CHB) photovoltaic grid-connected inverter can be independently supplied with Power by one photovoltaic component, Maximum Power Point Tracking (MPPT) of a component level, monitoring of the component level and turn-off of the component are easy to realize, and the single-phase CHB photovoltaic grid-connected inverter is particularly suitable for low-voltage low-Power household photovoltaic Power generation occasions. However, under the influence of factors such as partial shielding or damage, the output power of some photovoltaic modules is seriously reduced, and since the currents flowing through each H-bridge are equal and the transmission power difference is large, the power unit corresponding to the photovoltaic module with normal output power is overmodulatied, which leads to the performance deterioration of the output current and even the unstable operation of the system.
At present, how to enable a single-phase CHB photovoltaic grid-connected inverter to normally operate under a power imbalance condition has become a research hotspot of the single-phase CHB photovoltaic grid-connected inverter. Document "zhao, zhanxing, mao wang, xujun, both, zhaobraong, jiangcai.cascade H-bridge photovoltaic inverter power imbalance control strategy based on reactive compensation. 5076 and 5085. "(Chinese Motor engineering journal, 37, No. 17, page 5076 and 5085) proposes a centralized control strategy with reactive compensation function, and all H-bridge converters are ensured not to be overmodulatied when power is seriously unbalanced according to the principles of active proportional distribution and reactive demand distribution. However, this method may reduce the power factor of the system, limiting its practical application.
Documents "Tao Zhao, Xing Zhang, Wang Mao, Fusheng Wang, Jun Xu, and Yilei gu.a modified hybrid modulation strategy for applying dc voltage modulation of modulated H-bridge photovoltaic inverter" (Tao Zhao, Xing Zhang, Wang Mao, Fusheng Wang, Jun Xu, Yilei Gu, an improved hybrid modulation strategy for cascaded H-bridge photovoltaic inverters, vol.65, No.5, pp.3932-3941, may.2018. "(Tao Zhao, Xing Zhang, Wang Mao, Fusheng wao, Jun Xu, Yilei Gu, an improved hybrid modulation strategy for cascaded H-bridge photovoltaic inverters, IEEE industrial electronics journal, 65 th volume 5 of year 5, p.65 to p.3941) propose an improved hybrid modulation strategy that combines sine wave modulation with high frequency modulation to avoid an unbalanced H-bridge power conversion range under certain conditions of H-bridge modulation, and a linear H-bridge modulation range of low frequency can be further expanded. However, when this method is adopted, the dc bus capacitor voltage of the H-bridge converter still fluctuates greatly and there is a static difference in control, which reduces the power generation amount and MPPT efficiency.
Documents "Tao Zhao, Xing Zhang, Wang Mao, Fusheng Wang, Jun Xu, Yilei Gu, and Xinyu wang.an optimized third harmonic compensation strategy for single-phase cascaded H-bridge photovoltaic inverters", Tao Zhao, Xing Zhang, Wang Mao, Fusheng wa, Jun Xu, Yilei Gu, and Xinyu Wang, an optimized third-month harmonic compensation strategy for single-phase cascaded H-bridge photovoltaic inverters, IEEE 8635-8645, nov.2018 "(Tao Zhao, Xing Zhang, Wang Mao, Fusheng wa, Jun Xu, Yilei Gu, and Xinyu Wang), IEEE industrial electronics, 2018 converter make a linear harmonic compensation to a third-month harmonic compensation system that can work by compensating for a linear harmonic in a linear bridge over-current range of 1H-bridge dc-ac voltage, and can not be expanded by a factor of 1H-ac. However, this method has a weak capability to cope with power imbalance, and is not suitable for a scenario in which power is severely imbalanced.
The Chinese invention patent CN201710947222.8, namely a square wave compensation control method for expanding the operation range of the cascaded H-bridge type photovoltaic inverter, published and authorized in 8/2 in 2019 and the Chinese invention patent CN201710948192.2, namely a harmonic compensation control method for the cascaded H-bridge type photovoltaic grid-connected inverter, published and authorized in 8/27 in 2019 respectively provide different harmonic compensation strategies, the advantages of the third harmonic compensation strategy are retained by the two methods, the linear modulation range of the H-bridge converter can be expanded to 4/pi, and the capacity of the two methods for power imbalance is obviously higher than that of the third harmonic compensation strategy. However, with further imbalance of the output power of the photovoltaic module, the modulation degree of the partial H-bridge converter is larger than 4/pi, and the method is also ineffective.
The documents "Abbas Eskandari, Vahid java dian, hossei im-Eini, and broad yadolaihi.stable operation of grid connection cascade H-bridge inverter under unbalanced photovoltaic operation conditions, 20133rd international conference on electric power and energy conversion system, Istanbul, turnkey, October2-4, 2013." (Abbas Eskandari, Vahid java dian, hossei im-Eini, and milyaad yadolaihi, stable operation of a cascade H-bridge inverter under unbalanced lighting conditions, third policy and energy conversion system international conference in 2013, turkish, eistanzan, 2013 year 10 th-10 th month, and improved photovoltaic output control module reduces the output of a photovoltaic module compared to the output of a MPPT module in a modified version. However, this method may reduce the power generation of the system.
In summary, the existing single-phase cascaded photovoltaic grid-connected inverter and the control strategy thereof applied to the low-voltage household photovoltaic power generation occasions have the following disadvantages:
(1) the reactive power compensation strategy can deal with serious power imbalance conditions, but the method can reduce the power factor of the system, and the practical application can be limited.
(2) The linear modulation range of the H-bridge converter can be expanded from 1 to 4/pi by the improved hybrid modulation strategy, but the voltage fluctuation of a direct-current bus capacitor of the H-bridge converter is large, static control exists, and the power generation and MPPT efficiency of a system can be reduced.
(3) The third harmonic compensation strategy can not only aggravate the fluctuation of the DC bus capacitor voltage of the H-bridge converter, but also ensure the unit power factor operation of the system, but the method has weak capability of coping with power imbalance.
(4) The harmonic compensation strategy retains the advantages of the third harmonic compensation strategy and further expands the linear modulation range of the H-bridge converter, but the harmonic compensation strategy also fails in more severe power imbalance situations (e.g., some H-bridge converters have a modulation greater than 4/pi).
(5) Although the improved MPPT control strategy can deal with a severe power imbalance scene, the method reduces the power generation amount of the system.
Disclosure of Invention
The invention aims to solve the problem of overcoming the limitations of various schemes and provides a control method of a single-phase cascade type photovoltaic grid-connected inverter. The control method of the single-phase cascade type photovoltaic grid-connected inverter can ensure that the system can still normally operate under the condition of serious unbalanced illumination intensity, is suitable for household photovoltaic grid-connected power generation occasions, and has better comprehensive performance. In order to solve the technical problem of the invention, the adopted technical scheme is as follows:
a control method of a single-phase cascade type photovoltaic grid-connected inverter comprises N modules with the same structure, wherein N is a positive integer larger than 1, each module is formed by connecting a four-switch tube Buck-Boost converter in series with an H-bridge converter, direct current input ends of all the modules are respectively connected with a photovoltaic component in parallel, alternating current output ends of all the modules are connected in series, one end of each module is connected with a power grid through a filter inductor after being connected in series, the other end of each module is connected with the power grid through a single-phase active filter, the control method comprises average value control of direct current bus capacitor voltage of the H-bridge converter, grid-connected current control, improved nearest level approximation modulation, single-phase active filter control and four-switch tube Buck-Boost converter control, and the specific steps are as follows:
step 1, controlling the average value of the DC bus capacitor voltage of the H-bridge converter
Step 1.1, respectively sampling the DC bus capacitor voltage of N H-bridge converters to obtain DC bus capacitor voltage sampling values V of the N H-bridge convertersHi，i＝1，2，...，N；
Step 1.2, calculating to obtain an average value V of voltage sampling values of direct current bus capacitors of N H-bridge convertersHAverThe calculation formula is as follows:
Figure BDA0002832882740000041
step 1.3, using an H-bridge voltage regulator to obtain an average value V of voltage sampling values of direct current bus capacitors of N H-bridge convertersHAverControlled to a reference voltage VrefThe output of the H-bridge voltage regulator is the amplitude I of the grid-connected current instruction value of the single-phase cascade type photovoltaic grid-connected inverterMThe calculation formula is as follows:
Figure BDA0002832882740000051
wherein, KHVPIs the proportionality coefficient of the H-bridge voltage regulator, KHVIIs the integral coefficient of the H-bridge voltage regulator, and s is a Laplace operator;
step 2, grid-connected current control
Step 2.1, respectively sampling the power grid voltage and the grid-connected current to obtain a power grid voltage sampling value vgAnd grid-connected current sampling value ig；
Step 2.2, using a digital phase-locked loop to compare the grid voltage sampling value v obtained in the step 2.1gPhase locking is carried out to obtain a phase angle theta of the power grid voltage and an amplitude value V of the power grid voltageg；
Step 2.3, grid-connected current sampling value igThe phase angle is delayed by pi/2 while the amplitude value is kept unchanged, and a grid-connected current sampling value i is obtainedgOrthogonal signal iQI is togAnd iQConverting the two-phase static coordinate system into a two-phase rotating coordinate system to obtain an active current feedback value idAnd a reactive current feedback value iqThe calculation formula is as follows:
Figure BDA0002832882740000052
wherein cos (theta) is a cosine value of a power grid voltage phase angle theta, and sin (theta) is a sine value of the power grid voltage phase angle theta;
step 2.4, setting a reactive current reference value for enabling the single-phase cascade type photovoltaic grid-connected inverter to operate at a unit power factor
Figure BDA0002832882740000053
Is 0, active current reference value
Figure BDA0002832882740000054
The amplitude I of the grid-connected current instruction value of the single-phase cascade type photovoltaic grid-connected inverter calculated in the step 1.3MUsing an active current regulator to feed back an active current value idControl to active current reference value
Figure BDA0002832882740000055
Feeding back a reactive current value i using a reactive current regulatorqControl to reactive current reference value
Figure BDA0002832882740000056
Amplitude v directed to the active modulation voltagedAnd the amplitude v of the reactive modulation voltageqThe calculation formula is as follows:
Figure BDA0002832882740000061
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 2.5, calculating the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverterrAnd amplitude V of modulation wave of single-phase cascade type photovoltaic grid-connected inverterRMThe calculation formula is as follows:
Figure BDA0002832882740000062
wherein, arctan (v)q/vd) Denotes vq/vdThe arctan value of;
step 3, improved type nearest level approximation modulation
Step 3.1, dividing the modulation wave vr of the single-phase cascade type photovoltaic grid-connected inverter calculated in the step 2.5 into four intervals in one period, and referring the four intervals to be an interval I, an interval II, an interval III and an interval IV, and defining as follows:
interval I: v. ofrV is not less than 0rMonotonically increasing
Interval II: v. ofrV is not less than 0rMonotonically decreasing
Interval III: v. ofr< 0 and vrMonotonically decreasing
Interval IV: v. ofr< 0 and vrMonotonically increasing
Step 3.2, obtaining the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverter through calculation according to the interval I, the interval II, the interval III and the interval IV which are divided in the step 3.1 and the step 2.5rCalculating the actual modulation wave v of the single-phase cascade type photovoltaic grid-connected inverterRealThe calculation formula is as follows:
Figure BDA0002832882740000063
step 3.3, VHjAnd (3) representing a voltage sampling value of a direct-current bus capacitor of the jth H-bridge converter, wherein j is 1, 2RealAnd judging the operation modes of the N H-bridge converters:
(1) when v isrWhen located in the interval I
If expression
Figure BDA0002832882740000071
If yes, the operation mode H of the ith H-bridge converter Mi1 is ═ 1; otherwise, the operation mode H of the ith H-bridge converterMi＝0，i＝1，2，...，N；
(2) When v isrWhen located in interval II
If expression
Figure BDA0002832882740000072
If yes, the operation mode H of the ith H-bridge converter Mi0; otherwise, the operation mode H of the ith H-bridge converterMi＝1，i＝1，2，...，N；
(3) When v isrWhen located in interval III
If expression
Figure BDA0002832882740000073
If yes, the operation mode H of the ith H-bridge converterMi-1; otherwise, the operation mode H of the ith H-bridge converterMi＝0，i＝1，2，...，N；
(4) When v isrWhen located in the interval IV
If expression
Figure BDA0002832882740000074
If yes, the operation mode H of the ith H-bridge converter Mi0; otherwise, the operation mode H of the ith H-bridge converterMi＝-1，i＝1，2，...，N；
Wherein, | vRealL is vRealAbsolute value of (d); h Mi1 denotes the ac output voltage v of the ith H-bridge converterHOi＝VHi；H Mi0 denotes the ac output voltage v of the ith H-bridge converterHOi＝0；HMi-1 represents the alternating output voltage v of the ith H-bridge converterHOi-VHi；
Step 4, single-phase active filter control
Step 4.1, calculating by using recursive discrete Fourier transform to obtain grid-connected current sampling value igFundamental component i ofgFThen calculating a grid-connected current sampling value igThe harmonic component i containedgHThe calculation formula is as follows:
igH＝ig-igF
step 4.2, harmonic component i contained in grid-connected current sampling value is subjected to proportional controlgHControl is carried out, and the output of the controller is a harmonic voltage signal vgHThe calculation formula is as follows:
vgH＝KFPigH
wherein, KFPIs the proportionality coefficient of the proportional controller;
step 4.3, for single phase haveSampling the DC bus capacitor voltage of the source filter to obtain a DC bus capacitor voltage sampling value V of the single-phase active filterF；
Step 4.4, using an active filtering voltage regulator to sample the voltage value V of the direct current bus capacitor of the single-phase active filterFControlled to a reference voltage VrefThe output of the active filter voltage regulator is the amplitude V of the voltage command valueCThe calculation formula is as follows:
Figure BDA0002832882740000081
wherein, KFVPIs the scale factor, K, of an active filter voltage regulatorFVIIs the integral coefficient of the active filter voltage regulator;
step 4.5, calculating the amplitude V of the voltage command value output by the active filter voltage regulator according to the phase angle theta of the power grid voltage obtained in the step 2.2 and the amplitude V of the voltage command value output by the active filter voltage regulator obtained in the step 4.4CCalculating to obtain fundamental voltage signal vCFThe calculation formula is as follows:
vCF＝VCcos(θ)
step 4.6, obtaining the harmonic voltage signal v by calculation according to the step 4.2gHAnd step 4.5, calculating to obtain a fundamental voltage signal vCFAdding to obtain the total modulation voltage v of the single-phase active filtergFThen divided by the voltage sampling value V of the DC bus capacitor of the single-phase active filterFThen, obtaining the modulation wave m of the single-phase active filtergFThe calculation formula is as follows:
mgF＝(vgH+vCF)/VF
step 5, four-switch tube Buck-Boost converter control
Step 5.1, respectively sampling the direct-current bus capacitor voltage of the N four-switch tube Buck-Boost converters and the output current of the N photovoltaic modules to obtain direct-current bus capacitor voltage sampling values V of the N four-switch tube Buck-Boost convertersPViAnd output current sampling values I of N photovoltaic modulesPVi，i＝1，2，...，N；
Step 5.2, obtaining voltage sampling values V of the direct current bus capacitor of the N four-switch tube Buck-Boost converter according to the step 5.1PViAnd output current sampling values I of N photovoltaic modulesPViRespectively carrying out maximum power point tracking control on the N photovoltaic assemblies to obtain maximum power point voltages of the N photovoltaic assemblies
Figure BDA0002832882740000095
i＝1，2，...，N；
Step 5.3, obtaining the maximum power point voltage of the N photovoltaic modules obtained in the step 5.2
Figure BDA0002832882740000096
As a reference value of the direct-current bus capacitor voltage of the four-switch tube Buck-Boost converter, N same DC/DC voltage regulators are used for respectively carrying out sampling value V on the direct-current bus capacitor voltage of the N four-switch tube Buck-Boost convertersPViControlling the N DC/DC voltage regulators to output current inner loop instruction values of the N four-switch tube Buck- Boost converters
Figure BDA0002832882740000091
Figure BDA0002832882740000091
Figure BDA0002832882740000091
1, 2, N, calculated as:
Figure BDA0002832882740000092
wherein, KDVPIs the proportionality coefficient of the DC/DC voltage regulator, KDVIIs the integral coefficient of the DC/DC voltage regulator;
and 5.4, respectively sampling the inductive currents of the N four-switch tube Buck-Boost converters to obtain inductive current sampling values i of the N four-switch tube Buck-Boost convertersLDi，i＝1，2，...，N；
Step 5.5, using N same DC/DC current regulators to sample the inductive current i of N four-switch tube Buck-Boost convertersLDiControl is the current inner loop instruction value of four-switch tube Buck-Boost converter
Figure BDA0002832882740000094
The outputs of the N DC/DC current regulators are respectively the duty ratio d of the N four-switch tube Buck- Boost converters i1, 2, N, calculated as:
Figure BDA0002832882740000093
wherein, KDIPIs the proportionality coefficient of the DC/DC current regulator, KDIIIs the integral coefficient of the DC/DC current regulator.
Compared with the prior art, the invention has the beneficial effects that:
(1) the single-phase cascade type photovoltaic grid-connected inverter and the control method thereof can deal with the working scene of serious unbalance of the output power of the photovoltaic component, and can enlarge the operation range of the system to a greater degree compared with the traditional single-phase cascade H-bridge photovoltaic grid-connected inverter.
(2) Even in a working scene with seriously unbalanced output power of the photovoltaic components, all the photovoltaic components can still work at the self maximum power point, and the generated energy of the system is maximized.
(3) By adopting the scheme of connecting the single-phase active filter in series, not only can the low-order harmonic of the output voltage of the inverter be filtered, but also the harmonic component of the voltage of the power grid can be filtered, and the better performance of the current of the power grid is ensured.
(4) Compared with the existing nearest level approximation modulation strategy, the improved nearest level approximation modulation strategy can ensure that the pulse widths output by all H-bridge converters have smaller difference, and further ensure that the consistency of the power transmission capability of the H-bridge converters is better.
Drawings
Fig. 1 shows a main circuit topology of a single-phase cascade type photovoltaic grid-connected inverter implemented by the present invention.
Fig. 2 is a main circuit topology of a single phase active filter embodying the present invention.
Fig. 3 is a control block diagram of a single-phase cascade-type photovoltaic grid-connected inverter implemented by the present invention.
Fig. 4 is a flowchart of a control method of a single-phase cascade-type photovoltaic grid-connected inverter implemented by the present invention.
FIG. 5 shows a modulation wave v of a single-phase cascaded grid-connected photovoltaic inverter according to an embodiment of the present inventionrInterval division schematic diagram and actual modulation wave v of single-phase cascade type photovoltaic grid-connected inverterRealSchematic diagram of the waveform of (1).
FIG. 6 illustrates the AC output voltages v of four H-bridge converters in a four-module cascade system, using the improved recent level modulation strategy implemented in the present inventionHO1、vHO2、vHO3、vHO4And the ac total output voltage v of the inverterH。
FIG. 7 illustrates an example of an AC output voltage v of four H-bridge converters in a four-module cascade system, using a conventional recent level modulation strategyHO1、vHO2、vHO3、vHO4And the ac total output voltage v of the inverterH。
FIG. 8 is an ith H-bridge converter operating mode H implemented in accordance with the present inventionMi＝1、H Mi0 and HMiWhen the value is-1, the ith H-bridge converter switch driving signal is generated.
FIG. 9 shows the total AC output voltage v of a single-phase cascaded grid-connected PV inverter embodying the present inventionHAC output voltage v of single-phase active filterFAnd a waveform diagram of the grid-connected point voltage vT.
FIG. 10 is a duty cycle d of an ith four-switch Buck-Boost converter in accordance with an embodiment of the inventioniA method of generating corresponding four switching tube driving signals.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly and clearly understood, the present invention will be further clearly and completely described below with reference to the accompanying drawings and embodiments.
FIG. 1 shows a main circuit topology structure of a single-phase cascaded photovoltaic grid-connected inverter, which includes N modules with the same structure, where N is a positive integer greater than 1, and each moduleThe converter is composed of a four-switch tube Buck-Boost converter connected in series with an H-bridge converter. Wherein, the ith ( i 1, 2,.., N) four-switch tube Buck-Boost converter is composed of a direct current bus capacitor CPViA filter inductor LDiAnd four fully-controlled switching devices S with anti-parallel diodesDij(j ═ 1, 2, 3, 4); the ith H-bridge converter is composed of a DC bus capacitor CHiAnd four fully-controlled switching devices S with anti-parallel diodesHijAnd (4) forming. Direct-current bus capacitor C of four-switch tube Buck-Boost converterPViEach of which is connected in parallel with a photovoltaic module PViFor supplying power to the entire system. In addition, the alternating current output ends of all the modules are connected in series, and one end of the alternating current output ends passes through the filter inductor L after the alternating current output ends are connected in seriesgAnd the other end of the single-phase active filter is connected with the power grid through the single-phase active filter. In FIG. 1, vgAnd igRespectively representing a sampling value of the power grid voltage and a sampling value of the grid-connected current; vPViAnd IPViRespectively representing a direct-current bus capacitor voltage sampling value of an ith four-switch tube Buck-Boost converter and an output current sampling value of a photovoltaic module connected with the direct-current bus capacitor voltage sampling value; i.e. iLDiRepresenting an inductive current sampling value of an ith four-switch tube Buck-Boost converter; vHiRepresenting a voltage sampling value of a direct current bus capacitor of the ith H-bridge converter; v. ofHOiRepresents the ac output voltage of the H-bridge converter of the ith H-bridge converter; v. ofHRepresenting the AC total output voltage, v, of a single-phase cascaded grid-connected photovoltaic inverterTAnd the grid-connected point voltage of the single-phase cascade type photovoltaic grid-connected inverter is represented.
FIG. 2 shows the main circuit topology of a single-phase active filter implemented by the present invention, which consists of a DC bus capacitor CF1Four full-control type switching devices S with anti-parallel diodesFj(j ═ 1, 2, 3, 4), filter inductance L of single-phase active filterFAnd a filter capacitor C of the single-phase active filterF2And (4) forming. Wherein, VFRepresenting the voltage sample value of the DC bus capacitor of a single-phase active filter, vFRepresenting the ac output voltage of a single-phase active filter.
FIG. 3 is a schematic representation of an embodiment of the present inventionThe control block diagram of the phase cascade type photovoltaic grid-connected inverter comprises average value control of all H-bridge converter DC bus capacitor voltages and power grid voltage v by using a digital phase-locked loopgPhase locking and grid current igSwitching device S for performing control, improved nearest level approximation modulation strategy and generating N H-bridge convertersHijDrive signal Q ofHij(i 1, 2., N, j 1, 2, 3, 4), control of the dc bus capacitor voltage of N four-switch tube Buck-Boost converters, and switching device S for generating N four-switch tube Buck-Boost convertersDijDrive signal Q ofDijAnd control and generation switching device S of a single-phase active filterFjDrive signal Q ofFj。
Fig. 4 is a flowchart of a control method of a single-phase cascade-type photovoltaic grid-connected inverter implemented by the present invention. As can be seen from fig. 3 and 4, the control method of the invention includes average value control of the dc bus capacitor voltage of the H-bridge converter, grid-connected current control, improved nearest level approximation modulation, single-phase active filter control and four-switch tube Buck-Boost converter control, and includes the following steps:
step 1, controlling the average value of the DC bus capacitor voltage of the H-bridge converter
Step 1.1, respectively sampling the DC bus capacitor voltage of N H-bridge converters to obtain DC bus capacitor voltage sampling values V of the N H-bridge convertersHi，i＝1，2，...，N。
Step 1.2, calculating to obtain an average value V of voltage sampling values of direct current bus capacitors of N H-bridge convertersHAverThe calculation formula is as follows:
Figure BDA0002832882740000131
step 1.3, using an H-bridge voltage regulator to obtain an average value V of voltage sampling values of direct current bus capacitors of N H-bridge convertersHAverControlled to a reference voltage VrefThe output of the H-bridge voltage regulator is the amplitude I of the grid-connected current instruction value of the single-phase cascade type photovoltaic grid-connected inverterMThe calculation formula is as follows:
Figure BDA0002832882740000132
wherein, KHVPIs the proportionality coefficient of the H-bridge voltage regulator, KHVIIs the integral coefficient of the H-bridge voltage regulator and s is the laplacian operator. In this embodiment, KHVP＝10，KHVI＝350。
Step 2, grid-connected current control
Step 2.1, respectively sampling the power grid voltage and the grid-connected current to obtain a power grid voltage sampling value vgAnd grid-connected current sampling value ig。
Step 2.2, using a digital phase-locked loop to compare the grid voltage sampling value v obtained in the step 2.1gPhase locking is carried out to obtain a phase angle theta of the power grid voltage and an amplitude value V of the power grid voltageg。
Step 2.3, grid-connected current sampling value igThe phase angle is delayed by pi/2 while the amplitude value is kept unchanged, and a grid-connected current sampling value i is obtainedgOrthogonal signal iQI is togAnd iQConverting the two-phase static coordinate system into a two-phase rotating coordinate system to obtain an active current feedback value idAnd a reactive current feedback value iqThe calculation formula is as follows:
Figure BDA0002832882740000133
wherein cos (theta) is a cosine value of the grid voltage phase angle theta, and sin (theta) is a sine value of the grid voltage phase angle theta.
In the embodiment, the grid current slave i is realized by using a second-order generalized integratorgConversion to a signal i of equal amplitude but phase-delayed by pi/2QAn all-pass filter may also be used to achieve this function.
Step 2.4, setting a reactive current reference value for enabling the single-phase cascade type photovoltaic grid-connected inverter to operate at a unit power factor
Figure BDA0002832882740000134
Is 0, active current reference value
Figure BDA0002832882740000135
The amplitude I of the grid-connected current instruction value of the single-phase cascade type photovoltaic grid-connected inverter calculated in the step 1.3MUsing an active current regulator to feed back an active current value idControl to active current reference value
Figure BDA0002832882740000141
Feeding back a reactive current value i using a reactive current regulatorqControl to reactive current reference value
Figure BDA0002832882740000142
Obtaining the amplitude v of the active modulation voltagedAnd the amplitude v of the reactive modulation voltageqThe calculation formula is as follows:
Figure BDA0002832882740000143
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; in this embodiment, KIP1＝1.5，KII1＝50，KIP2＝1.5，KII2＝50。
Step 2.5, calculating the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverterrAnd amplitude V of modulation wave of single-phase cascade type photovoltaic grid-connected inverterRMThe calculation formula is as follows:
Figure BDA0002832882740000144
wherein, arctan (v)q/vd) Denotes vq/vdThe arctan value of (c).
Step 3, improved type nearest level approximation modulation
Step 3.1, the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverter obtained by the calculation in the step 2.5rThe four intervals are divided into four intervals in one cycle, and the four intervals are called an interval I, an interval II, an interval III, and an interval IV, and are defined as follows:
interval I: v. ofrV is not less than 0rMonotonically increasing
Interval II: v. ofrV is not less than 0rMonotonically decreasing
Interval III: v. ofr< 0 and vrMonotonically decreasing
Interval IV: v. ofr< 0 and vrMonotonically increasing
Step 3.2, obtaining the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverter through calculation according to the interval I, the interval II, the interval III and the interval IV which are divided in the step 3.1 and the step 2.5rCalculating the actual modulation wave v of the single-phase cascade type photovoltaic grid-connected inverterRealThe calculation formula is as follows:
Figure BDA0002832882740000151
FIG. 5 shows a modulation wave v of a single-phase cascaded grid-connected photovoltaic inverter according to an embodiment of the present inventionrInterval division schematic diagram and actual modulation wave v of single-phase cascade type photovoltaic grid-connected inverterRealSchematic diagram of the waveform of (1).
Step 3.3, VHjAnd (3) representing a voltage sampling value of a direct-current bus capacitor of the jth H-bridge converter, wherein j is 1, 2RealAnd judging the operation modes of the N H-bridge converters:
(1) when v isrWhen located in the interval I
If expression
Figure BDA0002832882740000152
If yes, the operation mode H of the ith H-bridge converter Mi1 is ═ 1; otherwise, the operation mode H of the ith H-bridge converterMi＝0，i＝1，2，...，N；
(2) When v isrWhen located in interval II
If expression
Figure BDA0002832882740000153
If yes, the operation mode H of the ith H-bridge converter Mi0; otherwise, the operation mode H of the ith H-bridge converterMi＝1，i＝1，2，...，N；
(3) When v isrWhen located in interval III
If expression
Figure BDA0002832882740000154
If yes, the operation mode H of the ith H-bridge converterMi-1; otherwise, the operation mode H of the ith H-bridge converterMi＝0，i＝1，2，...，N；
(4) When v isrWhen located in the interval IV
If expression
Figure BDA0002832882740000155
If yes, the operation mode H of the ith H-bridge converter Mi0; otherwise, the operation mode H of the ith H-bridge converterMi＝-1，i＝1，2，...，N；
Wherein, | vRealL is vRealAbsolute value of (d); h Mi1 denotes the ac output voltage v of the ith H-bridge converterHOi＝VHi；H Mi0 denotes the ac output voltage v of the ith H-bridge converterHOi＝0；HMiWith-1 the ac output voltage v of the ith H-bridge converter is indicatedHOi＝-VHi；
FIG. 6 illustrates the AC output voltages v of four H-bridge converters in a four-module cascade system, using the improved recent level modulation strategy implemented in the present inventionHO1、vHO2、vHO3、vHO4And the ac total output voltage v of the inverterH. FIG. 7 is a block diagram at four module levelsTaking the coupled system as an example, the alternating current output voltages v of four H-bridge converters when the traditional recent level modulation strategy is adoptedHO1、vHO2、vHO3、vHO4And the ac total output voltage v of the inverterH. It can be seen that, although the conventional nearest level approximation modulation strategy and the improved nearest level approximation modulation strategy provided by the invention are adopted, the total alternating output voltage v of the inverterHIs identical, but when the traditional recent level approximation debugging strategy is adopted, the alternating current output voltages v of the four H-bridge convertersHO1、vHO2、vHO3And vHO4The pulse width of the converter is greatly different, which means that the power transmitted by the four H-bridge converters is greatly different; when the improved nearest level approach debugging strategy provided by the invention is adopted, the alternating current output voltages v of the four H-bridge convertersHO1、vHO2、vHO3And vHO4The pulse width difference of the H-bridge converter is small, and the power difference transmitted by the H-bridge converter is also small.
Working modes H of all H-bridge converters are obtained through calculation according to the step 3.3MiThereafter, the switching drive signals of the N H-bridge converters are generated according to the method for generating the switching drive signals of the ith H-bridge converter implemented by the present invention shown in fig. 8. Taking the ith H-bridge converter as an example: if the working mode H Mi1, switching tube SHi1Drive signal Q ofHi1Is at a high level, SHi1Conducting, switching tube SHi2Drive signal Q ofHi2Is at a low level, SHi2Turn-off, switch tube SHi3Drive signal Q ofHi3Is at a low level, SHi3Turn-off, switch tube SHi4Drive signal Q ofHi4Is at a high level, SHi4Conducting; if the working mode H Mi1, switching tube SHi1Drive signal Q ofHi1Is at a low level, SHi1Turn-off, switch tube SHi2Drive signal Q ofHi2Is at a high level, SHi2Conducting, switching tube SHi3Drive signal Q ofHi3Is at a high level, SHi3Conducting, switching tube SHi4Drive signal Q ofHi4Is at a low level, SHi4And (6) turning off. If workerAs mode HMiWhen the driving signal of the switching tube is 0, two generation methods are provided: method 1, switching tube SHi1Drive signal Q ofHi1Is at a high level, SHi1Conducting, switching tube SHi2Drive signal Q ofHi2Is at a low level, SHi2Turn-off, switch tube SHi3Drive signal Q ofHi3Is at a high level, SHi3Conducting, switching tube SHi4Drive signal Q ofHi4Is at a low level, SHi4Turning off; method 2, switching tube SHi1Drive signal Q ofHi1Is at a low level, SHi1Turn-off, switch tube SHi2Drive signal Q ofHi2Is at a high level, SHi2Conducting, switching tube SHi3Drive signal Q ofHi3Is at a low level, SHi3Turn-off, switch tube SHi4Drive signal Q ofHi4Is at a high level, SHi4And conducting.
Step 4, single-phase active filter control
Step 4.1, calculating by using recursive discrete Fourier transform to obtain grid-connected current sampling value igFundamental component i ofgFThen calculating a grid-connected current sampling value igThe harmonic component i containedgHThe calculation formula is as follows:
igH＝ig-igF
the recursive discrete fourier transform as used herein refers to a commonly used method in harmonic analysis and extraction, which has been reported by a large number of scientific research documents, such as the document "skillful, zhang, li ming, liu xiao xi, zhao xi. 123- "power system automation (44, volume 7, page 123-129, 2020) and documents" ", exquisitely, zhangxing, li ming, liu xiao xi, guo xu. 7-11. "(journal of Electrical engineering 2020, Vol.14, No. 2, pages 7-11).
Step 4.2, harmonic component i contained in grid-connected current sampling value is subjected to proportional controlgHTo controlThe output of the controller is a harmonic voltage signal vgHThe calculation formula is as follows:
vgH＝KFPigH
wherein, KFPIn this embodiment, K is the scaling factor of the proportional controllerFP＝10。
Step 4.3, sampling the direct current bus capacitor voltage of the single-phase active filter to obtain a direct current bus capacitor voltage sampling value V of the single-phase active filterF。
Step 4.4, using an active filtering voltage regulator to sample the voltage value V of the direct current bus capacitor of the single-phase active filterFControlled to a reference voltage VrefThe output of the active filter voltage regulator is the amplitude V of the voltage command valueCThe calculation formula is as follows:
Figure BDA0002832882740000181
wherein, KFVPIs the scale factor, K, of an active filter voltage regulatorFVIIs the integral coefficient of the active filtering voltage regulator. KFVP＝2.4，KFVI＝120。
Step 4.5, calculating the amplitude V of the voltage command value output by the active filter voltage regulator according to the phase angle theta of the power grid voltage obtained in the step 2.2 and the amplitude V of the voltage command value output by the active filter voltage regulator obtained in the step 4.4CCalculating to obtain fundamental voltage signal vCFThe calculation formula is as follows:
vCF＝VCcos(θ)
step 4.6, obtaining the harmonic voltage signal v by calculation according to the step 4.2gHAnd step 4.5, calculating to obtain a fundamental voltage signal vCFAdding to obtain the total modulation voltage v of the single-phase active filtergFThen divided by the voltage sampling value V of the DC bus capacitor of the single-phase active filterFThen, obtaining the modulation wave m of the single-phase active filtergFThe calculation formula is as follows:
mgF＝(vgH+vCF)/VF
calculating to obtain a modulation wave m of the single-phase active filtergFThen, four switching devices S are obtained according to Pulse Width Modulation (PWM) commonly used in power electronics technologyFj(j ═ 1, 2, 3, 4) of switching drive signal QFj。
FIG. 9 shows the total AC output voltage v of a single-phase cascaded grid-connected PV inverter embodying the present inventionHAC output voltage v of single-phase active filterFAnd the voltage v of the grid-connected pointTSchematic diagram of the waveform of (1). The single-phase active filter is mainly used for filtering out the AC total output voltage v of the single-phase cascade type photovoltaic grid-connected inverterHThe low-order harmonic component ensures that the performance of the current of the power grid is better.
Step 5, four-switch tube Buck-Boost converter control
Step 5.1, respectively sampling the direct-current bus capacitor voltage of the N four-switch tube Buck-Boost converters and the output current of the N photovoltaic modules to obtain direct-current bus capacitor voltage sampling values V of the N four-switch tube Buck-Boost convertersPViAnd output current sampling values I of N photovoltaic modulesPVi，i＝1，2，...，N。
Step 5.2, obtaining voltage sampling values V of the direct current bus capacitor of the N four-switch tube Buck-Boost converter according to the step 5.1PViAnd output current sampling values I of N photovoltaic modulesPViRespectively carrying out maximum power point tracking control on the N photovoltaic assemblies to obtain maximum power point voltages of the N photovoltaic assemblies
Figure BDA0002832882740000191
i＝1，2，...，N。
Step 5.3, obtaining the maximum power point voltage of the N photovoltaic modules obtained in the step 5.2
Figure BDA0002832882740000192
As a reference value of the direct-current bus capacitor voltage of the four-switch tube Buck-Boost converter, N same DC/DC voltage regulators are used for respectively carrying out sampling value V on the direct-current bus capacitor voltage of the N four-switch tube Buck-Boost convertersPViControlling the N DC/DC voltage regulators to output current inner loop instruction values of the N four-switch tube Buck- Boost converters
Figure BDA0002832882740000193
Figure BDA0002832882740000193
Figure BDA0002832882740000193
1, 2, N, calculated as:
Figure BDA0002832882740000194
wherein, KDVPIs the proportionality coefficient of the DC/DC voltage regulator, KDVIIs the integral coefficient of the DC/DC voltage regulator. In this embodiment, KDVP＝5，KDVI＝20。
And 5.4, respectively sampling the inductive currents of the N four-switch tube Buck-Boost converters to obtain inductive current sampling values i of the N four-switch tube Buck-Boost convertersLDi，i＝1，2，...，N。
Step 5.5, using N same DC/DC current regulators to sample the inductive current i of N four-switch tube Buck-Boost convertersLDiControl is the current inner loop instruction value of four-switch tube Buck-Boost converter
Figure BDA0002832882740000196
The outputs of the N DC/DC current regulators are respectively the duty ratio d of the N four-switch tube Buck- Boost converters i1, 2, N, calculated as:
Figure BDA0002832882740000195
wherein, KDIPIs the proportionality coefficient of the DC/DC current regulator, KDIIIs the integral coefficient of the DC/DC current regulator. In this embodiment, KDIP＝5，KDII＝20。
FIG. 10 is a duty cycle d of an ith four-switch Buck-Boost converter in accordance with an embodiment of the inventioniA method of generating corresponding four switching tube driving signals. When the duty ratio is 0 < di≤0At time 5, the four-switch Buck-Boost converter operates in Buck mode, and the equivalent duty cycle at this time can be expressed as di1＝2diSwitching device SDi1Drive signal Q ofDi1Can be controlled by duty cycle di1And carrier vcD1Obtained by comparison when di1＞vcD1When is, QDi1At a high level, the switching device SDi1Conducting; when d isi1≤vcD1When is, QDi1At a low level, the switching device SDi1And (6) turning off. Switching device SDi2Drive signal Q ofDi2Is and QDi1Complementary signals, i.e. QDi1At high level, QDi2Is low level, QDi1At low level, QDi2Is high. In this operating mode, the switching device SDi3Drive signal Q ofDi3Always at high level, i.e. switching devices SDi3Conducting all the time; switching device SDi4Drive signal Q ofDi4Always at low level, i.e. switching devices SDi4Is always turned off. When the duty ratio is 0.5 < diWhen the duty ratio is less than or equal to 1, the four-switch Buck-Boost converter works in a Boost mode, and the equivalent duty ratio at the moment can be expressed as di2＝2di-1. In this operating mode, the switching device SDi1Drive signal Q ofDi1Always at high level, i.e. switching devices SDi1Conducting all the time; switching device SDi2Drive signal Q ofDi2Always at low level, i.e. switching devices SDi2Is always turned off. Switching device SDi4Drive signal Q ofDi4Can be controlled by duty cycle di2And carrier vcD2Obtained by comparison when di2＞vcD2When is, QDi4At a high level, the switching device SDi4Conducting; when d isi2＞vcD2When is, QDi4At a low level, the switching device SDi4And (6) turning off. Switching device SDi3Drive signal Q ofDi3Is and QDi4Complementary signals, i.e. QDi4At high level, QDi3Is low level, QDi4At low level, QDi3Is high.

Claims (1)

1. A control method of a single-phase cascade type photovoltaic grid-connected inverter comprises N modules with the same structure, wherein N is a positive integer larger than 1, each module is formed by connecting a four-switch tube Buck-Boost converter in series with an H-bridge converter, direct current input ends of all the modules are respectively connected with a photovoltaic component in parallel, alternating current output ends of all the modules are connected in series, one end of each module is connected with a power grid through a filter inductor after being connected in series, and the other end of each module is connected with the power grid through a single-phase active filter.
Step 1, controlling the average value of the DC bus capacitor voltage of the H-bridge converter
Step 1.1, respectively sampling the DC bus capacitor voltage of N H-bridge converters to obtain DC bus capacitor voltage sampling values V of the N H-bridge convertersHi，i＝1，2，...，N；
Step 1.2, calculating to obtain an average value V of voltage sampling values of direct current bus capacitors of N H-bridge convertersHAverThe calculation formula is as follows:
Figure FDA0002832882730000011
step 1.3, using an H-bridge voltage regulator to obtain an average value V of voltage sampling values of direct current bus capacitors of N H-bridge convertersHAverControlled to a reference voltage VrefThe output of the H-bridge voltage regulator is the amplitude I of the grid-connected current instruction value of the single-phase cascade type photovoltaic grid-connected inverterMThe calculation formula is as follows:
Figure FDA0002832882730000012
wherein, KHVPRatio of H-bridge voltage regulatorExample coefficient, KHVIIs the integral coefficient of the H-bridge voltage regulator, and s is a Laplace operator;
step 2, grid-connected current control
Step 2.1, respectively sampling the power grid voltage and the grid-connected current to obtain a power grid voltage sampling value vgAnd grid-connected current sampling value ig；
Step 2.2, using a digital phase-locked loop to compare the grid voltage sampling value v obtained in the step 2.1gPhase locking is carried out to obtain a phase angle theta of the power grid voltage and an amplitude value V of the power grid voltageg；
Step 2.3, grid-connected current sampling value igThe phase angle is delayed by pi/2 while the amplitude value is kept unchanged, and a grid-connected current sampling value i is obtainedgOrthogonal signal iQI is togAnd iQConverting the two-phase static coordinate system into a two-phase rotating coordinate system to obtain an active current feedback value idAnd a reactive current feedback value iqThe calculation formula is as follows:
Figure FDA0002832882730000021
wherein cos (theta) is a cosine value of a power grid voltage phase angle theta, and sin (theta) is a sine value of the power grid voltage phase angle theta;
step 2.4, setting a reactive current reference value for enabling the single-phase cascade type photovoltaic grid-connected inverter to operate at a unit power factor
Figure FDA0002832882730000022
Is 0, active current reference value
Figure FDA0002832882730000023
The amplitude I of the grid-connected current instruction value of the single-phase cascade type photovoltaic grid-connected inverter calculated in the step 1.3MUsing an active current regulator to feed back an active current value idControl to active current reference value
Figure FDA0002832882730000024
Feeding back a reactive current value i using a reactive current regulatorqControl to reactive current reference value
Figure FDA0002832882730000025
Obtaining the amplitude v of the active modulation voltagedAnd the amplitude v of the reactive modulation voltageqThe calculation formula is as follows:
Figure FDA0002832882730000026
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 2.5, calculating the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverterrAnd amplitude V of modulation wave of single-phase cascade type photovoltaic grid-connected inverterRMThe calculation formula is as follows:
Figure FDA0002832882730000027
wherein, arctan (v)q/vd) Denotes vq/νdThe arctan value of;
step 3, improved type nearest level approximation modulation
Step 3.1, the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverter obtained by the calculation in the step 2.5rThe four intervals are divided into four intervals in one cycle, and the four intervals are called an interval I, an interval II, an interval III, and an interval IV, and are defined as follows:
interval I: v. ofrV is not less than 0rMonotonically increasing
Interval II: v. ofrV is not less than 0rMonotonically decreasing
Interval III: v. ofr< 0 and vrMonotonically decreasing
Interval IV: v. ofr< 0 and vrMonotonically increasing
Step 3.2, obtaining the modulation wave v of the single-phase cascade type photovoltaic grid-connected inverter through calculation according to the interval I, the interval II, the interval III and the interval IV which are divided in the step 3.1 and the step 2.5rCalculating the actual modulation wave v of the single-phase cascade type photovoltaic grid-connected inverterRealThe calculation formula is as follows:
Figure FDA0002832882730000031
step 3.3, VHjAnd (3) representing a voltage sampling value of a direct-current bus capacitor of the jth H-bridge converter, wherein j is 1, 2RealAnd judging the operation modes of the N H-bridge converters:
(1) when v isrWhen located in the interval I
If expression
Figure FDA0002832882730000032
If yes, the operation mode H of the ith H-bridge converterMi1 is ═ 1; otherwise, the operation mode H of the ith H-bridge converterMi＝0，i＝1，2，...，N；
(2) When v isrWhen located in interval II
If expression
Figure FDA0002832882730000033
If yes, the operation mode H of the ith H-bridge converterMi0; otherwise, the operation mode H of the ith H-bridge converterMi＝1，i＝1，2，...，N；
(3) When v isrWhen located in interval III
If expression
Figure FDA0002832882730000041
If yes, the operation mode H of the ith H-bridge converterMi-1; whether or notThen, the operation mode H of the ith H-bridge converterMi＝0，i＝1，2，...，N；
(4) When v isrWhen located in the interval IV
If expression
Figure FDA0002832882730000042
If yes, the operation mode H of the ith H-bridge converterMi0; otherwise, the operation mode H of the ith H-bridge converterMi＝-1，i＝1，2，...，N；
Wherein, | vRealL is vRealAbsolute value of (d); hMi1 denotes the ac output voltage v of the ith H-bridge converterHOi＝VHi；HMi0 denotes the ac output voltage v of the ith H-bridge converterHOi＝0；HMi-1 represents the alternating output voltage v of the ith H-bridge converterHOi-VHi；
Step 4, single-phase active filter control
Step 4.1, calculating by using recursive discrete Fourier transform to obtain grid-connected current sampling value igFundamental component i ofgFThen calculating a grid-connected current sampling value igThe harmonic component i containedgHThe calculation formula is as follows:
igH＝ig-igF
step 4.2, harmonic component i contained in grid-connected current sampling value is subjected to proportional controlgHControl is carried out, and the output of the controller is a harmonic voltage signal vgHThe calculation formula is as follows:
vgH＝KFPigH
wherein, KFPIs the proportionality coefficient of the proportional controller;
step 4.3, sampling the direct current bus capacitor voltage of the single-phase active filter to obtain a direct current bus capacitor voltage sampling value V of the single-phase active filterF；
Step 4.4, using an active filtering voltage regulator to sample the voltage value V of the direct current bus capacitor of the single-phase active filterFControl as reference electricityPressure VrefThe output of the active filter voltage regulator is the amplitude V of the voltage command valueCThe calculation formula is as follows:
Figure FDA0002832882730000051
wherein, KFVPIs the scale factor, K, of an active filter voltage regulatorFVIIs the integral coefficient of the active filter voltage regulator;
step 4.5, calculating the amplitude V of the voltage command value output by the active filter voltage regulator according to the phase angle theta of the power grid voltage obtained in the step 2.2 and the amplitude V of the voltage command value output by the active filter voltage regulator obtained in the step 4.4CCalculating to obtain fundamental voltage signal vCFThe calculation formula is as follows:
vCF＝VCcos(θ)
step 4.6, obtaining the harmonic voltage signal v by calculation according to the step 4.2gHAnd step 4.5, calculating to obtain a fundamental voltage signal vCFAdding to obtain the total modulation voltage v of the single-phase active filtergFThen divided by the voltage sampling value V of the DC bus capacitor of the single-phase active filterFThen, obtaining the modulation wave m of the single-phase active filtergFThe calculation formula is as follows:
mgF＝(vgH+vCF)/VF
step 5, four-switch tube Buck-Boost converter control
Step 5.1, respectively sampling the direct-current bus capacitor voltage of the N four-switch tube Buck-Boost converters and the output current of the N photovoltaic modules to obtain direct-current bus capacitor voltage sampling values V of the N four-switch tube Buck-Boost convertersPViAnd output current sampling values I of N photovoltaic modulesPVi，i＝1，2，...，N；
Step 5.2, obtaining voltage sampling values V of the direct current bus capacitor of the N four-switch tube Buck-Boost converter according to the step 5.1PViAnd output current sampling values I of N photovoltaic modulesPViRespectively carrying out maximum power point tracking control on the N photovoltaic assemblies to obtain N photovoltaic groupsMaximum power point voltage of the device
Figure FDA0002832882730000052
i＝1，2，...，N；
Step 5.3, obtaining the maximum power point voltage of the N photovoltaic modules obtained in the step 5.2
Figure FDA0002832882730000053
As a reference value of the direct-current bus capacitor voltage of the four-switch tube Buck-Boost converter, N same DC/DC voltage regulators are used for respectively carrying out sampling value V on the direct-current bus capacitor voltage of the N four-switch tube Buck-Boost convertersPViControlling the N DC/DC voltage regulators to output current inner loop instruction values of the N four-switch tube Buck-Boost converters
Figure FDA0002832882730000061
The calculation formula is as follows:
Figure FDA0002832882730000062
wherein, KDVPIs the proportionality coefficient of the DC/DC voltage regulator, KDVIIs the integral coefficient of the DC/DC voltage regulator;
and 5.4, respectively sampling the inductive currents of the N four-switch tube Buck-Boost converters to obtain inductive current sampling values i of the N four-switch tube Buck-Boost convertersLDi，i＝1，2，...，N；
Step 5.5, using N same DC/DC current regulators to sample the inductive current i of N four-switch tube Buck-Boost convertersLDiControl is the current inner loop instruction value of four-switch tube Buck-Boost converter
Figure FDA0002832882730000064
The outputs of the N DC/DC current regulators are respectively the duty ratio d of the N four-switch tube Buck-Boost convertersi1, 2, N, calculated as:
Figure FDA0002832882730000063
wherein, KDIPIs the proportionality coefficient of the DC/DC current regulator, KDIIIs the integral coefficient of the DC/DC current regulator.
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