CN112117925B - DCM single-bridge-arm integrated split-source inverter control method for photovoltaic grid-connected occasions - Google Patents
DCM single-bridge-arm integrated split-source inverter control method for photovoltaic grid-connected occasions Download PDFInfo
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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
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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
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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
- H02M7/539—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 with automatic control of output wave form or frequency
- H02M7/5395—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 with automatic control of output wave form or frequency by pulse-width modulation
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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
- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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
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Abstract
The invention belongs to the technical field of electricity, and particularly relates to a control method of a DCM single-bridge-arm integrated split-source inverter for a photovoltaic grid-connected site, which comprises the following steps: acquiring output voltage and current of a photovoltaic cell, obtaining an input voltage reference through an MPPT algorithm, and realizing MPPT through PI control; obtaining the voltage of a direct current bus, comparing the voltage with the reference of the direct current bus, and outputting an amplitude instruction through PI control; acquiring the voltage of a power grid, and calculating to obtain unit sinusoidal signals with the same frequency and phase as the voltage of the power grid; multiplying the unit sine signal by an amplitude instruction to obtain a sine reference; and obtaining the grid current and comparing the grid current with a sine reference, and realizing the sine and pure active output of the grid current through PI control. By the method, the DCM single-bridge-arm integrated split-source inverter can be applied to photovoltaic grid-connected occasions, overmodulation of output waveforms during light-load operation can be effectively avoided, and the output waveform quality is high. In addition, the design method of the input filter inductor can ensure that the control method is smoothly implemented in the whole working range.
Description
Technical Field
The invention relates to the technical field of electricity, in particular to a control method of a DCM single-bridge-arm integrated split-source inverter, and particularly relates to a control method of a DCM single-bridge-arm integrated split-source inverter applied to a photovoltaic grid-connected occasion.
Background
In order to meet the voltage grade requirement of power equipment or a power grid, a Boost converter cascade voltage is commonly adopted in a distributed photovoltaic power generation systemA two-stage structure of a Source Inverter (VSI). The scheme can be well adapted to the wide variation range of the input voltage, the control is simpler, but the number of power devices is more, and the overall efficiency is difficult to further improve. In recent years, researchers have proposed a single-bridge integrated split-source inverter that filters the input filter inductor LinThe middle point of one bridge arm connected to the single-phase VSI through the diode is essentially equivalent to the integration of a DC-DC Boost converter (such as a Boost, a Buck-Boost and the like) and the one bridge arm of the single-phase VSI through a multiplexing power tube. The single-bridge arm integrated split-source inverter has the following advantages: the input current is continuous, the voltage gain is higher, the number of passive devices is small, no circulation current exists, no through zero vector exists, and the number of switching tubes and the switching state are the same as those of a traditional VSI. Therefore, in recent years, the single-phase single-bridge-arm integrated split-source inverter becomes a research hotspot in the field of inverters.
Under a traditional single-phase VSI modulation strategy (such as single-polarity frequency multiplication SPWM and the like), the duty ratio of a lower tube of a bridge arm of a single-bridge-arm integrated split-source inverter changes in a sine rule, so that input filter inductance current contains low-frequency pulsating components with large amplitude, and current stress and on-state loss are increased; moreover, the voltage of the direct current bus changes along with the modulation ratio M, so that the voltage stress of the switching tube and the direct current bus capacitor under the heavy-load working condition is increased sharply. The scholars propose a PWM + SPWM modulation strategy based on the superposition principle. Under the modulation strategy, a bridge arm (called a boost bridge arm) connected with the input filter inductor always works in a PWM mode to play a role in DC boost conversion; the other bridge arm (called as an inverter bridge arm) always works in an SPWM mode, and outputs the required alternating voltage under the coordination of the boost bridge arm. The modulation strategy can solve the problems faced by the traditional SPWM single-phase single-bridge arm SSI, but the voltage gain under a Continuous Conduction Mode (CCM) of input filter inductive current is less than 1, and the boost function is not provided. If the input filter inductor is designed in a Discontinuous Current Mode (DCM), the single-bridge-arm integrated split-source inverter can have a boost capability. However, the voltage gain is in a severe nonlinear relationship with the duty ratio D and the load, and D will drop greatly under light load, resulting in distortion of the output waveform due to overmodulation. Therefore, a power-variable control method is provided by the scholars, namely the switching frequency and the duty ratio of a boost bridge arm of the DCM single-phase single-bridge arm integrated split-source inverter are kept unchanged, and the closed-loop control of the direct-current bus voltage is realized by adjusting the grid-connected power of the boost bridge arm. The control method avoids the problem of overmodulation of the output waveform during light load, but the output power is required to be used as the control degree of freedom, so the control method is not suitable for the application occasions of photovoltaic grid-connected power generation (constant power supply power in the MPPT mode).
Disclosure of Invention
In view of the above, the invention provides a control method of a DCM single-bridge-arm integrated split-source inverter for a photovoltaic grid-connected application, which solves the application problem of the photovoltaic grid-connected power generation application, and can effectively avoid the output waveform overmodulation phenomenon, and the output waveform has high quality and stronger practicability.
To achieve the above object, the proposed solution is as follows:
a control method of a DCM single-bridge-arm integrated split-source inverter for a photovoltaic grid-connected occasion comprises a photovoltaic cell and an input filter capacitor CinInput filter inductor LinAnti-reverse diode D, boost bridge arm, inverter bridge arm and output filter inductor LfAnd the boost bridge arm comprises a first switching tube S1A second switch tube S2The inverter bridge arm comprises a third switching tube S3And a fourth switching tube S4Input filter capacitor CinThe positive electrode of the photovoltaic cell and the input filter inductor LinIs connected to one end of the input filter inductor LinThe other end of the first switch is connected with the anode of an anti-reverse diode D, and the cathode of the anti-reverse diode D is connected with the first switch tube S1Source electrode of and second switching tube S2A drain electrode of (1); input filter capacitor CinNegative pole of the photovoltaic cell, and a second switching tube S2Source electrode and fourth switching tube S4Source electrode and DC bus capacitor CdcIs connected with the negative electrode of the direct current bus capacitor CdcPositive pole and first switch tube S1Drain electrode of (1) and third switching tube S3The drain electrodes of the two electrodes are connected; output filter inductance LfOne end of the first switch tube S, the cathode of the anti-reverse diode D and the first switch tube S1Source electrode of and second switching tube S2The drain electrode of the grid is connected to the middle point of the boost bridge arm, the other end of the grid is connected with a power grid, and the other end of the power grid is connected to a third switching tube S3Source electrode and fourth switching tube S4The drain electrode of (a) the first electrode,
the control method comprises the following steps:
s1, acquiring output voltage and output current of a photovoltaic cell, and calculating through an MPPT algorithm to obtain an input voltage reference;
s2, calculating the difference between the input voltage reference and the output voltage of the photovoltaic cell to generate a first error; sending the first error to an input voltage controller, generating a first control signal by the input voltage controller, modulating the first control signal to generate a pulse frequency modulation signal, and driving the first switching tube and the second switching tube;
s3, acquiring the voltage of the direct current bus, and making a difference with the given voltage reference of the direct current bus to obtain a second error;
s4, sending the second error to a direct current bus voltage controller, generating a second control signal by the direct current bus voltage controller, and carrying out amplitude limiting on the second control signal through a first amplitude limiting module, wherein the first amplitude limiting module outputs a grid-connected current amplitude instruction;
s5, acquiring power grid voltage, calculating unit sinusoidal signals with the same frequency and phase as the power grid voltage, and multiplying the grid-connected current amplitude instruction by the unit sinusoidal signals to obtain a grid-connected current reference;
s6, acquiring grid-connected current, and calculating the difference between the grid-connected current reference and the grid-connected current to obtain a third error; and sending the third error to a grid-connected current controller, generating a third control signal by the grid-connected current controller, and modulating the third control signal to generate a pulse width modulation signal for driving a third switch tube and a fourth switch tube.
Further, in step S2, the modulating the first control signal to generate a pulse frequency modulation signal specifically includes:
s21, inputting the first control signal into a voltage/frequency value conversion module to obtain a corresponding carrier signal frequency value, carrying out upper and lower limit constraint on the carrier signal frequency value through a frequency limit module, sending an output frequency value of the frequency limit module into a triangular carrier generation module, and outputting a first bipolar triangular carrier signal with variable frequency;
and S22, comparing the direct current modulation signal with the average value equal to zero with the first bipolar triangular carrier signal to form a pulse frequency modulation signal with the constant duty ratio of 0.5.
Further, in step S5, the calculating a unit sinusoidal signal having the same frequency and phase as the grid voltage specifically includes: and according to the power grid voltage, acquiring the angular frequency of the power grid voltage through a PLL (phase locked loop), and further calculating a unit sinusoidal signal with the same frequency and phase as the power grid voltage.
Further, in step S6, the modulating the third control signal to generate a pulse width modulation signal specifically includes: and comparing the third control signal with a second bipolar triangular carrier signal with fixed frequency after passing through a second amplitude limiting module to form a pulse width modulation signal.
Furthermore, the frequency variation range of the first bipolar triangular carrier signal with variable frequency is 20-180 kHz.
Further, the frequency of the second bipolar triangular carrier signal with fixed frequency is 20 kHz.
Further, the input filter inductor LinThe design of (2) is as follows:
wherein f iss1,minIs the minimum value of the frequency limiting module, fs1,maxIs the maximum value of the frequency limiting module, variable
UdcAnd UinAre respectively DC bus voltage udcAnd an input voltage uinD is the second switch tube S of the boost bridge arm2(lower tube) on duty cycle, PoIs the output power.
The embodiment of the application refers to the output voltage u of the photovoltaic cellinAnd an input voltage reference uin,refMaking comparison by inputting a voltage controller Guin(s) realizing direct current boost control; will direct current bus voltage udcAnd a DC bus voltage reference udc,refComparing, and controlling the voltage of the DC busudc(s) controlling to obtain a grid-connected current amplitude instruction Igm(ii) a Will be connected to the grid current igWith sinusoidal reference
Comparing, via grid-connected current controller GigAnd(s) controlling to realize the sine and phase-locked control of the grid-connected current. Compared with the conventional method, the method provided by the invention enables the switching frequency f of the boost bridge arm (namely the bridge arm formed by the first switching tube and the second switching tube) to be lowers1As the control freedom degree, the output power is not restrained any more, the problem of output waveform distortion caused by overmodulation during light load when the DCM single-bridge-arm integrated split-source inverter for the photovoltaic grid-connected field is applied to the photovoltaic grid-connected power generation field is solved, the overmodulation phenomenon of the output waveform can be effectively avoided, and the quality of the output waveform is improved. In addition, the design method of the input filter inductor can ensure that the system always works in an inductor current discontinuous mode in the whole working range, so that the provided control method can be smoothly implemented.
Drawings
Fig. 1 is a schematic diagram of a DCM single-bridge-arm integrated split-source inverter for a photovoltaic grid-connected site and a control method thereof, disclosed in an embodiment of the present application; the inverter circuit structure schematic diagram is characterized in that (a) is a DCM single-bridge-arm integrated split-source inverter circuit structure schematic diagram for photovoltaic grid-connected occasions; (b) a schematic diagram of a control method of a DCM single-bridge-arm integrated split-source inverter for a photovoltaic grid-connected occasion;
fig. 2 is a theoretical waveform diagram of each key signal of a DCM single-bridge arm integrated split-source inverter for a photovoltaic grid-connected site disclosed in the embodiment of the present application;
FIG. 3 shows an input voltage U according to an embodiment of the present applicationinOutput power PoAnd variable FuA three-dimensional relationship diagram of (a);
FIG. 4(a) shows the input voltage u when the control method of the present invention is appliedinDC bus voltage udcInput filter inductor current iLinGrid voltage waveform ugAnd a grid-connected current igThe voltage of the maximum power point of the photovoltaic cell is 100V, and the power of the maximum power point is 520W;
FIG. 4(b) is a diagram of a power frequency positive half-cycle modulated signal u when the control method of the present invention is adoptedracAnd uc2、S2Switching tube driving signal ugs,S2、S4Switching tube driving signal ugs,S4And input filter inductor current iLinA simulated waveform diagram of (1);
FIG. 4(c) is a diagram of a power frequency negative half-cycle modulated signal u when the control method of the present invention is adoptedracAnd uc2、S2Switching tube driving signal ugs,S2、S4Switching tube driving signal ugs,S4And input filter inductor current iLinA simulated waveform diagram of (1);
FIG. 5(a) shows the input voltage u when the control method of the present invention is appliedinDC bus voltage udcInput filter inductor current iLinGrid voltage waveform ugAnd a grid-connected current igThe voltage of the maximum power point of the photovoltaic cell is 100V, and the power of the maximum power point is 130W;
FIG. 5(b) is a diagram of a power frequency positive half-cycle modulated signal u when the control method of the present invention is appliedracAnd uc2、S2Switching tube driving signal ugs,S2、S4Switching tube driving signal ugs,S4And input filter inductor current iLinA simulated waveform diagram of (1);
FIG. 5(c) is a diagram of a power frequency negative half-cycle modulated signal u when the control method of the present invention is adoptedracAnd uc2、S2Switching tube driving signal ugs,S2、S4Switching tube driving signal ugs,S4And input filter inductor current iLinSimulated waveform ofFigure (a).
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the application discloses a control method of a DCM single-bridge arm integrated split-source inverter for a photovoltaic grid-connected application, and as shown in (a) of fig. 1, the DCM single-bridge arm integrated split-source inverter for the photovoltaic grid-connected application includes a photovoltaic cell and an input filter capacitor CinInput filter inductor LinA reverse diode D, a first and a second switch tube S1、S2The third and fourth switch tubes S3、S4Inverter bridge arm formed, output filter inductor LfAnd a power grid. Input filter capacitor CinThe positive electrode of the photovoltaic cell and the input filter inductor LinIs connected to one end of the input filter inductor LinThe other end of the first switch is connected with the anode of an anti-reverse diode D, and the cathode of the anti-reverse diode D is connected with the first switch tube S1Source electrode of and second switching tube S2The drain (the connection point is named as the booster bridge arm midpoint a); input filter capacitor CinNegative pole of the photovoltaic cell, and a second switching tube S2Source electrode and fourth switching tube S4Source electrode and DC bus capacitor CdcIs connected with the negative electrode of the direct current bus capacitor CdcPositive pole and first switch tube S1Drain electrode of (1) and third switching tube S3The drain electrodes of the two electrodes are connected; output filter inductance LfOne end of the first switching tube is connected to the midpoint A of the boost bridge arm, the other end of the first switching tube is connected with a power grid, and the other end of the power grid is connected to the third switching tube S3Source electrode and fourth switching tube S4Is connected to the drain (the connection point is named inverter leg midpoint B).
As shown in fig. 1 (b), the control method includes the steps of:
s100, respectively collecting output voltage u of the photovoltaic cell through a voltage sensor and a current sensorinAnd an output current iinObtaining the input voltage reference u corresponding to the maximum power point through the calculation of the MPPT control algorithmin,ref；
S200, input voltage reference uin,refSubtracting the output voltage u of the photovoltaic cellinObtaining a first error e1(ii) a The first error e1Input voltage controller Guin(s) from the input voltage controller Guin(s) generating a first control signal c1And applying the first control signal c1The modulation generates a pulse frequency modulation signal.
In the present invention, the first control signal c1The pulse frequency modulation signal generated by modulation is specifically:
s201, a first control signal c is sent1Sending the signal into a voltage/frequency value conversion module, and processing the signal by the voltage/frequency value conversion module to obtain a first control signal c1Into corresponding carrier signal frequency values fs1；
S202, a carrier signal frequency value fs1Inputting the minimum value f of the frequency limiting module for processings1,minAnd a maximum value fs1,maxThe change range of the switching frequency of the boost bridge arm allowed by the system is determined; the output frequency value of the frequency limiting module is taken as a triangular carrier generation module VtriTo output a first bipolar triangular carrier signal u with a variable frequencyc1The first bipolar triangular carrier signal uc1The frequency is numerically the same as the output frequency value of the frequency limiting module.
S203, enabling the average value to be equal to zerordcAnd a first bipolar triangular carrier signal uc1Comparing to form a pulse frequency modulation signal u with a constant duty ratio of 0.5gs,S2And its inverted signal ugs,S1And a second switching tube S for integrating the split-source inverter for the DCM single-bridge arm2And a first switching tube S1Driving is carried out; in the present invention, an input voltage controller Guin(s) a proportional integral controller may be employed.
S300, providing a direct current bus voltage reference u according to the average value of the direct current bus voltage required in the system design indexdc,refAnd sampling the DC bus voltage u by a voltage sensordcAnd obtaining a second error e by subtracting the two2；
S400, calculating the second error e2Input DC bus voltage controller Gudc(s) from a DC bus voltage controller Gudc(s) generating a second control signal c2And a second control signal c2Inputting into a first amplitude limiting module for processing, and limiting the upper and lower limit values of the first amplitude limiting module, wherein the upper limit value is the maximum grid-connected current amplitude Igm,maxDetermining that the lower limit value is selected to be 0; the first amplitude limiting module outputs an amplitude instruction I serving as grid-connected currentgm(ii) a In the invention, a DC bus voltage controller Gudc(s) a proportional integral controller may be employed.
S500, acquiring power grid voltage u through a voltage sensorgThen obtaining the phase signal of the network voltage through a PLL circuit
ωgAnd
the voltage angular frequency and the phase angle of the power grid are respectively; according to the phase signal of the network voltage, a unit sine signal with the same frequency and phase as the network voltage is calculated
Then the amplitude instruction I of the grid-connected current is carried outgmUnit sine signal of voltage of power network
Multiplying to obtain a grid-connected current reference
S600, collecting grid-connected current i through a current sensorgAnd will be referenced to the grid current ig,refMinus the grid-connected current igTo obtain a third error e3(ii) a The third error e3Input grid-connected current controller Gig(s) from grid-connected current controller Gig(s) generating a third control signal c3(ii) a The third control signal c3Processing through a second amplitude limiting module; the upper limit value of the second amplitude limiting module is selected as a second bipolar carrier uc2Amplitude of Ucm(as shown in FIG. 2), the lower limit is selected to be-UcmThe output of the second amplitude limiting module is used as an alternating current modulation signal urac(ii) a Modulating an AC signal uracWith a second bipolar triangular carrier signal u of fixed frequencyc2Comparing to generate a pulse width modulation signal ugs,S4And its inverted signal ugs,S3And the fourth switching tube S is used for driving the DCM single-bridge-arm integrated split-source inverter for the photovoltaic grid-connected occasion4And a third switching tube S3. In the invention, a grid-connected current controller Gig(s) a proportional integral controller may be employed.
Continuously repeating the steps to finally control the input voltage u of the DCM single-bridge-arm integrated split-source inverterinAnd the DC bus voltage udcGrid-connected current as expectedigTo the grid voltage ugThe same frequency and the same phase.
The theoretical waveform diagram of each key signal of the DCM single-bridge-arm integrated split-source inverter in the control method provided by the invention is shown in figure 2.
It should be explained that, in order to illustrate the difference between the control method of the present invention and the conventional method, the following analysis process is performed on the DCM single-bridge integrated split-source inverter according to the photovoltaic grid-connected site shown in fig. 1:
because the input filter inductor works in a DCM mode, the direct-current boosting link of the DCM single-bridge-arm integrated split-source inverter for the photovoltaic grid-connected occasion has the same steady-state characteristic as that of the traditional DCM Boost converter
In the above formula，UdcAnd UinAre respectively DC bus voltage udcAnd an input voltage uinD is the second switch tube S of the boost bridge arm2(lower tube) on duty cycle, fs1For boost bridge arm switching frequency, PoIs the output power.
Specifically, the conventional grid connection method needs to output power P in formula (1)oAs a degree of freedom of control to realize control on the dc side. However, when the input of the DCM single-bridge integrated split-source inverter is the photovoltaic cell, the power supply power is constant in the MPPT mode, so the output power P is constantoThe control is not a degree of freedom, and therefore, the control requirement for grid-connected power generation cannot be met. In the invention, the switching frequency f of the boost bridge arm is adjusteds1As a degree of freedom of control to realize control on the DC side to output power PoThe method is not restricted any more, so that the application problem of photovoltaic grid-connected power generation occasions is solved. In addition, because the duty ratio D is fixed, the overmodulation phenomenon of the output waveform is effectively avoided, and the quality of the output waveform is improved.
It should be explained that the control method is implemented on the premise that the input filter inductor L is used as the input filter inductorinAlways operating in DCM mode. In order to ensure that the control method can realize direct-current side boosting and alternating-current side inversion of the single-bridge arm integrated split source inverter in the whole working range, the design process of the input filter inductor is provided:
according to formula (1), further obtained
Let variable Fu＝fs1Lin. As can be seen from the formula (3), the input filter inductance value LinIs dependent on the static operating point (U) of the systemin,Po,UdcD) and switching frequency fs1. To ensure under all working conditionsInput protection inductor LinOperating in DCM, it needs to satisfy:
Min(Fu)≤Linfs1≤Max(Fu) (4)
therefore, the method comprises the following steps:
in the formula (f)s1,minIs the minimum value of the frequency limiting module, fs1,maxMax (F) being the maximum value of the frequency-limiting blocku) Is a variable FuMaximum value of (D), Min (F)u) Is a variable FuIs measured.
This is the input filter inductance LinIs preferably within the above-mentioned range.
The present invention performs L based on the following design criteriainThe design of (2): allowable switching frequency range f of boost bridge arms120-180 kHz, and switching frequency f of inverter bridge arms220kHz, duty ratio D0.5, DC input voltage Uin75-100V, DC bus voltage Udc400V, effective value U of power grid voltageg110V, grid voltage angular frequency omegagIs 50Hz, output power Po＝130～520W。
FIG. 3 shows Uin，Po，FuThree-dimensional relationship diagram of the three. It can be seen that when U is usedin＝75V，PoWhen 520W, FuTake the minimum value, so Min (F)u) 1.66; when U is turnedin＝100V，Po130W, FuTake the maximum value, so Max (F)u) 12.82; thus, can obtain
72μH≤Lin≤83μH (9)
To sum up, take Lin＝0.80μH。
The feasibility of the control method of the present invention is verified by simulation. The main circuit energy storage element parameters are as follows: input capacitance C in80 muF, DC bus capacitance Cdc240 muF, input filter inductance L in80 muH, output filter inductance L f4 mH. In addition, an ideal voltage source (E200V) and a resistor (R) for the input-side photovoltaic celle＝19.23Ω(Po＝520W)，Re＝76.92Ω(Po130W) is equivalent. Fig. 4 and fig. 5 show simulation waveforms of the photovoltaic cell under two working conditions that the maximum power point voltage is 100V and the maximum power point power is 520W and 130W, respectively.
FIGS. 4(a) and 5(a) show input voltages u of the DCM single-bridge-arm integrated split-source inverter under two working conditions of 520W and 130W of maximum power point powerinDC bus voltage udcInput filter inductor current iLinGrid voltage waveform ugAnd a grid-connected current igThe waveform of (a); FIGS. 4(b) and 5(b) show power frequency positive half-cycle modulation signal u under two working conditions with maximum power point power of 520W and 130WracAnd uc2、S2Switching tube driving signal ugs,S2、S4Switching tube driving signal ugs,S4And the inductor current iLinThe waveform of (a); FIGS. 4(c) and 5(c) show the power frequency negative half-cycle modulation signal u under the two working conditions of 520W and 130W of maximum power point powerracAnd uc2、S2Switching tube driving signal ugs,S2、S4Switching tube driving signal ugs,S4And input filter inductor current iLinThe waveform of (2). It can be seen that under the above two operating conditions, iLinThe average value of the input voltage is 100V, the average value of the direct current bus voltage is 400V, and the average value is basically consistent with a control target value; grid-connected current igAnd electricityNetwork voltage ugThe same frequency and phase are obtained, and the output waveform is not distorted; each key signal waveform is identical to the theoretical waveform of fig. 2. In addition, the switching frequency of the boost bridge arm is less than or equal to f and less than or equal to 39.3kHzs1At most 155.34kHz, with fs1Theoretical range [20kHz,180kHz]And the input inductance design method is basically matched, so that the correctness of the input inductance design method is verified.
Therefore, by combining the analysis, the DCM single-bridge-arm integrated split-source inverter control method for the photovoltaic grid-connected site solves the application problem of the photovoltaic grid-connected power generation site by changing the system control freedom degree, can effectively avoid the overmodulation phenomenon of the output waveform, and has high output waveform quality. In addition, the design process of the input filter inductor provided by the invention can ensure that the control method is smoothly implemented in the whole working range.
Finally, it is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea, and not to limit it. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall into the protection scope of the present invention.
Claims (6)
1. A control method of a DCM single-bridge-arm integrated split-source inverter for a photovoltaic grid-connected occasion is characterized in that,
the DCM single-bridge-arm integrated split-source inverter for the photovoltaic grid-connected occasion comprises a photovoltaic battery and an input filter capacitor CinInput filter inductor LinAnti-reverse diode D, boost bridge arm, inverter bridge arm and output filter inductor LfAnd the boost bridge arm comprises a first switching tube S1A second switch tube S2The inverter bridge arm comprises a third switching tube S3And a fourth switching tube S4Input filter capacitor CinThe positive electrode of the photovoltaic cell and the input filter inductor LinIs connected to one end of the input filter inductor LinThe other end of the first switch is connected with the anode of an anti-reverse diode D, and the cathode of the anti-reverse diode D is connected with the first switch tube S1Source electrode of and second switching tube S2A drain electrode of (1); input filter capacitor CinNegative pole of the photovoltaic cell, and a second switching tube S2Source electrode and fourth switching tube S4Source electrode and DC bus capacitor CdcIs connected with the negative electrode of the direct current bus capacitor CdcPositive pole and first switch tube S1Drain electrode of (1) and third switching tube S3The drain electrodes of the two electrodes are connected; output filter inductance LfOne end of the first switch tube S, the cathode of the anti-reverse diode D and the first switch tube S1Source electrode of and second switching tube S2The drain electrode of the grid is connected to the middle point of the boost bridge arm, the other end of the grid is connected with a power grid, and the other end of the power grid is connected to a third switching tube S3Source electrode and fourth switching tube S4The drain electrode of (a) the first electrode,
the control method comprises the following steps:
s1, acquiring output voltage and output current of a photovoltaic cell, and calculating through an MPPT algorithm to obtain an input voltage reference;
s2, calculating the difference between the input voltage reference and the output voltage of the photovoltaic cell to generate a first error; sending the first error to an input voltage controller, generating a first control signal by the input voltage controller, modulating the first control signal to generate a pulse frequency modulation signal, and driving the first switching tube and the second switching tube;
wherein, the modulating the first control signal to generate a pulse frequency modulation signal specifically comprises:
s21, inputting the first control signal into a voltage/frequency value conversion module to obtain a corresponding carrier signal frequency value, carrying out upper and lower limit constraint on the carrier signal frequency value through a frequency limit module, sending an output frequency value of the frequency limit module into a triangular carrier generation module, and outputting a first bipolar triangular carrier signal with variable frequency;
s22, comparing the direct current modulation signal with the average value equal to zero with the first bipolar triangular carrier signal to form a pulse frequency modulation signal with the constant duty ratio of 0.5;
s3, acquiring the voltage of the direct current bus, and making a difference with the given voltage reference of the direct current bus to obtain a second error;
s4, sending the second error to a direct current bus voltage controller, generating a second control signal by the direct current bus voltage controller, and carrying out amplitude limiting on the second control signal through a first amplitude limiting module, wherein the first amplitude limiting module outputs a grid-connected current amplitude instruction;
s5, acquiring power grid voltage, calculating unit sinusoidal signals with the same frequency and phase as the power grid voltage, and multiplying the grid-connected current amplitude instruction by the unit sinusoidal signals to obtain a grid-connected current reference;
s6, acquiring grid-connected current, and calculating the difference between the grid-connected current reference and the grid-connected current to obtain a third error; and sending the third error to a grid-connected current controller, generating a third control signal by the grid-connected current controller, and modulating the third control signal to generate a pulse width modulation signal for driving a third switch tube and a fourth switch tube.
2. The method according to claim 1, wherein in step S5, the calculating of the unit sinusoidal signal having the same frequency and phase as the grid voltage specifically includes: and according to the power grid voltage, acquiring the angular frequency of the power grid voltage through a PLL (phase locked loop), and further calculating a unit sinusoidal signal with the same frequency and phase as the power grid voltage.
3. The method according to claim 1, wherein in step S6, the third control signal is modulated to generate a pwm signal, specifically: and comparing the third control signal with a second bipolar triangular carrier signal with fixed frequency after passing through a second amplitude limiting module to form a pulse width modulation signal.
4. The method for controlling the DCM single-bridge-arm integrated split-source inverter for the photovoltaic grid-connected application according to claim 1, wherein the frequency variation range of the first bipolar triangular carrier signal with variable frequency is 20-180 kHz.
5. The method for controlling the DCM single-bridge-arm integrated split-source inverter for the PV grid-connected application according to claim 3, wherein the frequency of the second bipolar triangular carrier signal with fixed frequency is 20 kHz.
6. The method for controlling the DCM single-bridge-arm integrated split-source inverter for the PV grid-connected application according to claim 1, wherein the input filter inductor L isinThe design of (2) is as follows:
wherein f iss1,minIs the minimum value of the frequency limiting module, fs1,maxIs the maximum value of the frequency limiting module, variable
UdcAnd UinAre respectively DC bus voltage udcAnd an input voltage uinD is the second switch tube S of the boost bridge arm2(lower tube) on duty cycle, PoIs the output power.
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