CN115021283B - Energy-storage-free photovoltaic voltage type control method and system - Google Patents
Energy-storage-free photovoltaic voltage type control method and system Download PDFInfo
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
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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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- 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 discloses a control method and a control system for a photovoltaic voltage type without energy storage, which adopt a rear-stage inverter to realize the control of direct-current side voltage and frequency double sagging; detecting a working mode of a photovoltaic inverter, and obtaining a working mode value FlagMPP of the photovoltaic and the movement condition of a current photovoltaic working point according to the sampled photovoltaic output voltage and the photovoltaic output power; determining the photovoltaic output voltage corresponding to the maximum power point according to the motion condition of the current photovoltaic working point; and according to the photovoltaic output voltage corresponding to the maximum power point, controlling the command value by the photovoltaic port voltage, and utilizing a PWM duty ratio signal, realizing the control strategy of the energy-storage-free photovoltaic inverter in two modes of load demand power being larger than the photovoltaic maximum power and load demand power being smaller than the photovoltaic maximum power. The reasonable distribution of the power of each inverter in the photovoltaic island micro-grid, the active support of the voltage frequency of the alternating current bus and the capability of the photovoltaic inverter to simultaneously process the power disturbance from two sides of a source load are realized.
Description
Technical Field
The invention belongs to the technical field of new energy power generation and converter control, and particularly relates to an energy-storage-free photovoltaic voltage type control method and system.
Background
In the new energy power generation technology, photovoltaic power generation is attracting attention because of wide energy distribution and easy utilization. However, the high reliance of photovoltaic power generation on electrical grids, energy storage and energy management systems severely limits its development. The photovoltaic inverter is very important in the utilization of solar energy, the photovoltaic array converts the solar energy into electric energy, and the inverter controls the output of the photovoltaic inverter to meet the load requirement, so that the solar energy can be better utilized by reasonably controlling the photovoltaic array and the converter.
In order to improve the utilization rate of solar energy of the photovoltaic array, the converters are controlled by taking the maximum power output by the photovoltaic array under a specific environment as a target, but in an island micro-grid, the principle of matching the source load power is contrary to the principle of matching the source load power, and in order to enable the photovoltaic inverter to actively support the voltage and the frequency of an alternating current bus, the MPP operation is gradually replaced by a more flexible active power control method. Active power control can be achieved by controlling the converter to match the photovoltaic output power to the load demand, without operating at a maximum power point, but to adjust the photovoltaic output power to track the load demand.
However, when the photovoltaic output power fluctuates greatly and sudden load changes occur, the photovoltaic system may not meet the power demand of the load and thus be disconnected from the load, which is a serious waste for the photovoltaic system that retains the power generation capability. In the case of such a power shortage, a corresponding control mode is required to switch the operation mode of the inverter, which has a great influence on the voltage-type controlled photovoltaic inverter.
Disclosure of Invention
The technical problem to be solved by the invention is to provide the energy-storage-free photovoltaic voltage type control method and system for realizing reasonable distribution of power of each inverter in the photovoltaic island micro-grid, actively supporting voltage frequency of an alternating current bus and simultaneously processing power disturbance from two sides of a source load by the photovoltaic inverter aiming at the defects in the prior art.
The invention adopts the following technical scheme:
The energy-storage-free photovoltaic voltage type control method comprises the following steps of:
s1, according to d and q axis reference output voltages u d_ref、uq_ref of an inverter, obtaining modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed loop control, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing a reference output voltage phase angle theta of the inverter through coordinate transformation, converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals, and adopting a rear-stage inverter to realize double droop control of direct-current side voltage and frequency;
S2, detecting a working mode of the photovoltaic inverter, and obtaining a working mode value FlagMPP of the photovoltaic and the motion condition of a current photovoltaic working point according to the sampled photovoltaic output voltage u pv and the photovoltaic output power p pv;
S3, according to the motion condition of the current photovoltaic working point obtained in the step S2, if the load demand power P L is larger than the photovoltaic maximum power P MPP, enabling the photovoltaic inverter to work at the maximum power point through MPPT control, and taking the photovoltaic port voltage control command value u pv_ref as the photovoltaic output voltage corresponding to the maximum power point; if the load demand power P L is smaller than the photovoltaic maximum power P MPP, switching the working mode, obtaining photovoltaic output power P pv and a photovoltaic working mode value Flag according to the command value P pv,ref of the photovoltaic array output power, and calculating a photovoltaic port voltage control command value u pv_ref as a photovoltaic output voltage corresponding to a maximum power point;
And S4, according to the photovoltaic output voltage u pv and the photovoltaic port voltage control command value u pv_ref corresponding to the maximum power point obtained in the step S3, using the PWM duty ratio signal obtained in the step S1 to realize the control strategy of the energy-storage-free photovoltaic inverter in two modes that the load demand power P L is larger than the photovoltaic maximum power P MPP and the load demand power P L is smaller than the photovoltaic maximum power P MPP.
Specifically, step S1 specifically includes:
S101, determining an inverter direct current side voltage reference value U 0, a sagging coefficient k d, virtual inertia J, a synchronous angular frequency w ref and an inverter direct current side capacitor C 0, and calculating a relation coefficient G u between the input power of the photovoltaic array to the inverter and the inverter direct current side voltage and a relation coefficient G w between the inverter direct current side voltage and the output frequency according to the relation coefficient;
S102, obtaining an inverter direct current side voltage reference value U 0 and a sampling inverter direct current side voltage U 0, differentiating U 0 and U 0, and calculating to obtain a photovoltaic array output power instruction value p pv_ref and an inverter reference output voltage phase angle theta by using a relation coefficient G u between the input power of a photovoltaic array to the inverter and the inverter direct current side voltage and a relation coefficient G w between the inverter direct current side voltage and the output frequency;
s103, sampling the output voltage u abc of an inverter port, outputting the current i abc, respectively obtaining the voltage u d、uq and the current i d、iq of d and Q axes through coordinate transformation, and then calculating to obtain the real-time output reactive power Q of the inverter;
S104, calculating to obtain d and Q-axis output reference voltages U d_ref、uq_ref of the inverter according to reactive power Q, sagging coefficient k d, rated voltage amplitude U of an alternating current bus of the inverter and a virtual impedance link;
S105, obtaining d and q axis reference output voltages u d_ref、uq_ref of the inverter, obtaining modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed loop control, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing the phase angle theta of the reference output voltages of the inverter obtained in the step S104 through coordinate transformation, and converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals.
Further, in step S104, the output reference voltages u d_ref、uq_ref of the inverter d and q axes are:
Wherein L v is virtual impedance, U is rated voltage amplitude of an alternating current bus of the inverter, Q is reactive power, k d is sagging coefficient, w ref is synchronous angular frequency, and i d、iq is value of output current of the inverter under dq synchronous rotation coordinate system.
Further, in step S105, the PWM duty cycle signal is:
Wherein M a、Mb、Mc is an inverter three-phase modulation wave, θ is M d、Mq, and a modulation command value is generated by the d-axis current inner loop.
Specifically, in step S2, the photovoltaic operation mode value FlagMPP is specifically:
wherein u old and p old are the photovoltaic port voltage and the photovoltaic power at the previous moment, u pv is the output voltage of the sampled photovoltaic, and p pv is the photovoltaic output power.
Further, the detection of the working mode of the photovoltaic inverter specifically includes:
S201, sampling a photovoltaic system to obtain output voltage u pv and current i pv of a current photovoltaic array, reading light Fu Duankou voltage u old and photovoltaic output power p old at the last moment of the photovoltaic system, and calculating to obtain output power p pv of the current photovoltaic array;
S202, judging whether u pv is larger than 5, if u pv is smaller than 5, judging that the photovoltaic inverter works at the left side of MPP at the moment, namely FlagMPP = -1, assigning the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and ending detection; if u pv >5, go to step S203;
S203, judging whether Deltau= |u pv-uold | is larger than 5, and if Deltau <5, directly cutting out of judgment; if Δu >5, go to step S204;
S204, judging whether k mpp＝(upv-uold)·(ppv-pold) is larger than 0; if k mpp is less than 0, continuing to judge the value of FlagMPP; if k mpp >0, the current photovoltaic power instruction value p pv_ref is read in, and the value of FlagMPP is judged.
Further, in step S204, if k mpp <0, when FlagMPP >0, let FlagAvF = -1, and assign the current light Fu Duankou voltage u pv and the current photovoltaic output power p pv to u old and p old, and the detection is completed; when FlagMPP is less than 0, reading in the value of FlagAvF, when FlagAvF is less than 0, making FlagAvF = FlagAvF +1, and assigning the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and ending the detection; when FlagAvF is more than or equal to 0, let u mpp＝upv、impp＝ipv、pmpp＝ppv, flagKno =1, flagAvF = -1, let FlagMPP =1 at the same time, finally assign the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and end the detection;
If k mpp >0, when FlagMPP is less than 0, flagAvF = -1 is given, the current light Fu Duankou voltage u pv and the photovoltaic output power p pv are assigned to u old and p old, and the detection is finished; when FlagMPP >0, reading in the value of FlagAvF, if FlagAvF <0, making FlagAvF = FlagAvF +1, and assigning the current light Fu Duankou voltage u pv and the current photovoltaic output power p pv to u old and p old, and ending the detection; when FlagAvF is more than or equal to 0, let u mpp＝upv、impp＝ipv、pmpp＝ppv, flagKno =1, flagAvF = -1, let FlagMPP = -1 at the same time, finally assign the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and end the detection.
Specifically, the step S3 specifically includes:
acquiring a reference voltage u pv_ref, and judging whether a working mode value FlagMPP of the photovoltaic is larger than 0;
If FlagMPP <0, judging whether the error switching flag bit FlagKno is greater than 0, if FlagKno >0, enabling u pv_ref＝UMPP,UMPP to be the voltage corresponding to the photovoltaic maximum power point, and enabling the photovoltaic working point movement state flag bit FlagRToL =1, and ending switching; if FlagKno <0, let u pv_ref＝upv_ref+cstep,cstep be the step parameter when the photovoltaic port voltage increases from 0, and the switching is finished;
If FlagMPP is more than 0, entering a DC/DC converter power loop to obtain a DC/DC converter power loop integral value u pv_ref_ac＝ki_dc_p·ppv_err,ki_dc_p as a power loop integral coefficient, and p pv_err as an error value between reference power and actual power, and judging FlagRToL; if FlagRToL >0, let FlagRToL =0, the photovoltaic port voltage command value remains unchanged, and the switching is finished; if FlagRToL <0, let u pv_ref＝kp_dc_p·ppv_err+upv_ref_ac,upv_ref_ac be the output value of the power loop integral term, k p_dc_p be the power loop proportional control coefficient, and the handover is completed.
Specifically, in step S4, the photovoltaic port voltage control command value u in_ref specifically is:
Wherein U MPP is the voltage corresponding to the maximum power point of the photovoltaic, k p_dc_p is the value of the proportional controller of the PI regulator of the power loop, k i_dc_p is the value of the integral controller of the PI regulator of the power loop, s is the integral link, p pv is the output power of the photovoltaic, and FlagMPP is the value of the working mode of the photovoltaic.
Another technical solution of the present invention is a photovoltaic control system without energy storage, comprising:
The conversion module is used for obtaining modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed-loop control according to d and q axis reference output voltages u d_ref、uq_ref of the inverter, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing a reference output voltage phase angle theta of the inverter through coordinate transformation, converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals, and realizing double droop control of direct-current side voltage and frequency by adopting a rear-stage inverter;
The detection module is used for detecting the working mode of the photovoltaic inverter, and obtaining a photovoltaic working mode value FlagMPP and the motion condition of the current photovoltaic working point according to the sampled photovoltaic output voltage u pv and the photovoltaic output power p pv;
The judging module is used for enabling the photovoltaic inverter to work at a maximum power point through MPPT control according to the motion condition of the current photovoltaic working point obtained by the detecting module if the load demand power P L is larger than the photovoltaic maximum power P MPP, and taking the photovoltaic port voltage control instruction value u pv_ref as the photovoltaic output voltage corresponding to the maximum power point; if the load demand power P L is smaller than the photovoltaic maximum power P MPP, switching the working mode, obtaining photovoltaic output power P pv and a photovoltaic working mode value Flag according to the command value P pv,ref of the photovoltaic array output power, and calculating a photovoltaic port voltage control command value u pv_ref as a photovoltaic output voltage corresponding to a maximum power point;
The control module is used for realizing the control strategy of the energy-storage-free photovoltaic inverter in two modes of load demand power P L being larger than photovoltaic maximum power P MPP and load demand power P L being smaller than photovoltaic maximum power P MPP by utilizing the PWM duty ratio signal obtained by the conversion module according to the photovoltaic output voltage u pv and the photovoltaic port voltage control command value u pv_ref corresponding to the maximum power point obtained by the judging module.
Compared with the prior art, the invention has at least the following beneficial effects:
According to the energy-storage-free photovoltaic voltage type control method, in an MPP running state, the photovoltaic inverter can process power disturbance from a source side and a load side simultaneously, the characteristics are applied to mode switching, and the cooperative work of a plurality of voltage control type photovoltaic inverters can be realized; even if the two-stage photovoltaic inverter is not supported by other energy sources, the two-stage photovoltaic inverter can actively adapt to the load demand and actively support a power grid; the photovoltaic inverter can adjust the output power of the photovoltaic cell in real time without the support of other energy sources, and match load requirements under various complex conditions, so that reasonable distribution of power of each inverter in the photovoltaic island micro-grid, active support of the voltage frequency of an alternating current bus and simultaneous processing of power disturbance from two sides of a source load by the photovoltaic inverter are realized.
Furthermore, the inverter side is directly responsible for regulating the capacitor voltage at the direct current side, and the reference output voltage phase angle of the inverter and the command value of the output power of the photovoltaic array are obtained according to the relation coefficient between the direct current voltage at the inverter side, the output frequency and the input power of the inverter, so that the photovoltaic inverter is beneficial to the fluctuation and the randomness of the photovoltaic output power and the load power.
Furthermore, the d-axis voltage command value of the inverter output can be obtained through a traditional reactive voltage droop control strategy, and virtual impedance is added into the d-axis voltage control loop and the q-axis voltage control loop to obtain the d-axis voltage command value and the q-axis voltage command value of the final inverter output in order to improve the stability of the control system.
Furthermore, the control steps are all performed in a d-axis coordinate system and a q-axis coordinate system, and after d-axis control command values and q-axis control command values are obtained, the d-axis coordinate system and the q-axis coordinate system are required to be subjected to coordinate transformation into a three-phase coordinate system so as to obtain modulated wave command values under the three-phase coordinate system, so that control of the three-phase inverter is realized.
Furthermore, the working area of the current photovoltaic inverter can be confirmed according to the result of comparing and calculating the current photovoltaic output voltage and the power value with the voltage power value at the last moment, and a judgment basis is provided for the selection of the control strategy of the photovoltaic inverter.
Further, the further detailed judging step is beneficial to helping the photovoltaic inverter to cope with environmental and self condition changes of the photovoltaic power supply, and accurately judges the working condition of the current photovoltaic inverter so as to select a corresponding control strategy.
Further, the judging step uses reasonable photovoltaic terminal voltage to detect the operation state of the photovoltaic inverter, and detection faults caused when the power characteristic curve of the photovoltaic battery changes due to environmental changes are avoided through a hysteresis function FlagAvF.
Further, control strategies for photovoltaic inverter port voltages in several modes of operation are presented.
Further, two control strategies under two working modes are combined, and a control instruction value of the photovoltaic port voltage is given.
In summary, the invention can realize smooth mode switching when the photovoltaic power is insufficient, and the lack of power can be borne by other photovoltaic inverters in the parallel system, thereby improving the flexibility of the photovoltaic inverter in the photovoltaic micro-grid and the reliability of the photovoltaic inverter in future new energy application.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
Fig. 1 is a schematic diagram of a circuit structure of a photovoltaic island micro-grid provided by the invention;
fig. 2 is a block diagram of a voltage type control strategy of a two-stage photovoltaic inverter provided by the invention;
Fig. 3 is a schematic diagram of a photovoltaic operation mode detection technique provided by the invention;
fig. 4 is a schematic flow chart of a photovoltaic operation mode detection technique provided by the invention;
Fig. 5 is a flowchart for switching the working modes of the photovoltaic inverter provided by the invention;
Fig. 6 is a simulated waveform diagram of the photovoltaic inverter provided by the invention in normal and power shortage modes, wherein (a) is the output power of the photovoltaic array and the inverter, (b) is the output frequency of the photovoltaic inverter, (c) is the output voltage of the photovoltaic array, (d) is the dc capacitor voltage of the inverter side, (e) is the flag bit of the MPP detection state, and (f) is the comparison between the command value of the output power of the photovoltaic and the actual value.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be understood that the terms "comprises" and "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
Various structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. The figures are not drawn to scale, wherein certain details are exaggerated for clarity of presentation and may have been omitted. The shapes of the various regions, layers and their relative sizes, positional relationships shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.
Referring to fig. 1, the present invention provides a non-energy-storage photovoltaic voltage type control method, and the application background topology considered is specifically: the photovoltaic power generation system comprises two photovoltaic inverters, and no other energy storage or power generation equipment exists. Each inverter is of a two-stage conversion structure and comprises a DC/DC converter and a DC/AC converter, the output end of the inverter adopts an LCL filtering topological structure, each inverter is connected with an alternating current bus to deliver power to a load, and in order to verify the control strategy provided by the invention, other power sources except photovoltaic are not adopted in the photovoltaic system; the photovoltaic inverter is enabled to work on the right side of the maximum photovoltaic power point by utilizing the unique characteristic of the photovoltaic curve, the power of the photovoltaic output power tracking load is controlled, the photovoltaic system can independently operate without an additional voltage source or an energy storage device, and smooth switching of control strategies of the photovoltaic in different working areas and under the condition of insufficient photovoltaic power can be met. The control method has good steady-state performance and dynamic performance and high engineering application value.
The invention discloses a non-energy-storage photovoltaic voltage type control method, which comprises the following steps of:
s1, adopting a rear inverter to realize double droop control of direct-current side voltage and frequency, ensuring constant direct-current side voltage and active power balance;
the direct-current side voltage and frequency dual droop control specifically comprises:
S101, determining an inverter direct current side voltage reference value U 0, a sagging coefficient k d, virtual inertia J, a synchronous angular frequency w ref and an inverter direct current side capacitor C 0, and calculating a relation coefficient G u between input power of a photovoltaic array to an inverter and inverter direct current side voltage and a relation coefficient G w between the inverter direct current side voltage and output frequency according to the relation coefficient G u, wherein the calculation formula is as follows:
S102, obtaining an inverter direct current side voltage reference value U 0 and a sampling inverter direct current side voltage U 0, differentiating U 0 and U 0, and calculating to obtain a photovoltaic array output power instruction value p pv_ref and an inverter reference output voltage phase angle theta by using a relation coefficient G u between input power of a photovoltaic array to the inverter and the inverter direct current side voltage and a relation coefficient G w between the inverter direct current side voltage and output frequency, wherein the calculation formula is as follows:
s103, sampling the output voltage u abc of an inverter port, outputting the current i abc, respectively obtaining the voltage u d、uq and the current i d、iq of d and Q axes through coordinate transformation, and then calculating to obtain the real-time output reactive power Q of the inverter;
the expression of the abc/dq transformation module is as follows:
Wherein i a、ib、ic is the value of the inverter output current in the abc three-phase stationary coordinate system, i d、iq is the value of the inverter output current in the dq synchronous rotation coordinate system, u a、ub、uc is the value of the inverter output voltage in the abc three-phase stationary coordinate system, u d、uq is the value θ of the inverter output voltage in the dq synchronous rotation coordinate system, and the angle between the d axis and the phase reference axis.
The reactive power is calculated as follows:
Q＝1.5×(vcq·icd-vcd·icq)
S104, calculating to obtain d and Q-axis output reference voltages U d_ref、uq_ref of the inverter according to reactive power Q, sagging coefficient k d, rated voltage amplitude U of an alternating current bus of the inverter and a virtual impedance link, wherein the calculation formula is as follows:
wherein L v is the virtual impedance.
S105, obtaining d and q-axis reference output voltages u d_ref、uq_ref of the inverter, obtaining modulated waves M d、Mq under d and q-axis by utilizing voltage and current double closed-loop control, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing the phase angle theta of the reference output voltages of the inverter obtained in the step S104 through coordinate transformation, and converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals;
The calculation formula for generating the current instruction by the voltage outer loop control module is as follows:
wherein i d_ref and i d_ref are respectively an inverter output current active component reference value and a reactive component reference value, k p_du is a value of an inverter output voltage active component PI regulator proportional controller, k i_du is a value of an inverter output voltage active component PI regulator integral controller, k p_qu is a value of an inverter output voltage reactive component PI regulator proportional controller, k i_qu is an inverter output voltage reactive component PI regulator integral controller, u d_ref is an inverter output voltage active component reference value, u d is an inverter output voltage active component, u q_ref is an inverter output voltage reactive component reference value, and u q is an inverter output voltage reactive component.
The calculation formula for generating the modulation signal by the current inner loop control module is as follows:
Wherein, M d、Mq is the d-axis current inner loop generated modulation command value, the q-axis current inner loop generated modulation command value, k p_di、ki_di is the d-axis current inner loop PI regulator proportional controller value and the integral controller value respectively, and k p_qi、ki_qi is the q-axis current inner loop PI regulator proportional controller value and the integral controller value respectively.
And performing dq/abc inverse transformation on M d and M q to generate a driving PWM duty ratio signal, wherein the calculation formula is as follows:
Referring to fig. 2, the DC/DC converter realizes droop control, and the inverter controls the DC side voltage to be constant. The strategy applies a power transmission mechanism of a synchronous machine, and the direct current capacitor in the two-stage photovoltaic inverter is similar to a conventional generator set as a mechanical rotor of the photovoltaic inverter. Therefore, the frequency of the inverter output voltage is determined by the dc side capacitor voltage, thereby controlling the output power of the photovoltaic array. The front-stage DC/DC converter is directly responsible for droop control and frequency regulation, as with the prime mover, while the inverter is responsible for regulating the DC side capacitor voltage. The dc side voltage can simultaneously regulate the output power of the photovoltaic and the output power of the inverter, which means that the source side and the load side can simultaneously regulate the power balance.
The inverter control strategy specifically comprises:
Firstly, calculating control parameters G u between the input power of the photovoltaic array to the inverter and the voltage of the inverter DC side and control parameters G w between the voltage of the inverter DC side and the output frequency according to a selected sagging coefficient k d, virtual inertia J, a synchronous angular frequency w ref, an inverter DC side capacitor C 0 and an inverter DC side voltage rated value U 0; obtaining the direct-current side voltage u 0 of the inverter according to the sampling, and calculating the reference output power p pv_ref of the photovoltaic power generation unit and the reference output voltage phase theta of the inverter; sampling three-phase voltage U abc and three-phase current i abc on the side of an alternating current bus output by an inverter, calculating to obtain reactive power Q, obtaining rated voltage amplitude voltage U of the alternating current bus, and calculating to obtain reference output voltage amplitude U dq of the inverter; and synthesizing the obtained inverter reference output voltage phase theta and the inverter reference output voltage amplitude U dq into an inner loop voltage command U ref.
The DC/DC converter control strategy specifically comprises the following steps:
The DC/DC converter ensures power balance for control of direct-current side capacitor voltage, three closed loop PI control of power, voltage and current is mainly adopted, a calculated photovoltaic power instruction value and the photovoltaic real-time power obtained through current sampling calculation are subjected to difference, a photovoltaic port voltage control instruction value is obtained through a PI regulator, the voltage instruction value is tracked based on a voltage current loop of the PI regulator through an inner loop, the duty ratio of the DC/DC converter is obtained, and tracking of photovoltaic to load power is completed.
S2, adopting a working mode detection method of the photovoltaic inverter;
Firstly, sampling output voltage u pv of the photovoltaic, outputting current i pv, calculating output power p pv of the photovoltaic, and calculating and judging a photovoltaic working mode according to the sampled output voltage u pv and the output power p pv of the photovoltaic to obtain a working mode value FlagMPP of the photovoltaic and the movement condition of a current photovoltaic working point.
FlagMPP is calculated as follows:
Wherein u old and p old are the photovoltaic port voltage and the photovoltaic power at the previous time, respectively.
Referring to fig. 3, the detection principle of the photovoltaic working mode provided by the present invention specifically includes:
In order to realize source load power balance, the moving direction of the photovoltaic working point is determined by the load carried by the current photovoltaic inverter, and the controller records and updates the power value at the voltage monitoring point every monitoring step δv. Judging the current photovoltaic working area according to the current photovoltaic voltage and power value and the photovoltaic voltage and power value recorded by the controller at the previous moment, and obtaining a corresponding photovoltaic working mode value FlagMPP; and according to the detection result of the photovoltaic working area, corresponding control feedback loops are automatically selected for the photovoltaics of different working areas, and a photovoltaic port voltage control instruction value u pv_ref is calculated.
Referring to fig. 4, the working mode detection process using the photovoltaic inverter specifically includes:
S201, sampling a photovoltaic system to obtain output voltage u pv and current i pv of a current photovoltaic array, reading light Fu Duankou voltage u old and photovoltaic output power p old at the last moment of the photovoltaic system, and calculating to obtain output power p pv of the current photovoltaic array;
S202, judging whether u pv is larger than 5, if u pv is smaller than 5, judging that the photovoltaic inverter works at the left side of MPP at the moment, namely FlagMPP = -1, assigning the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and ending detection; if u pv >5, go to step S203;
S203, judging whether Deltau= |u pv-uold | is larger than 5, and if Deltau <5, directly cutting out of judgment; if Δu >5, go to step S204;
S204, judging whether k mpp＝(upv-uold)·(ppv-pold) is larger than 0;
S2041, if k mpp is less than 0, continuing to judge the value of FlagMPP;
S20411, if FlagMPP >0, let FlagAvF = -1, and assign the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and end the detection;
S20412, if FlagMPP is less than 0, reading the value of FlagAvF, if FlagAvF is less than 0, making FlagAvF = FlagAvF +1, assigning the current light Fu Duankou voltage u pv and the current photovoltaic output power p pv to u old and p old, and ending the detection; if FlagAvF is more than or equal to 0, let u mpp＝upv、impp＝ipv、pmpp＝ppv, flagKno =1, flagAvF =1, let FlagMPP =1 at the same time, finally assign the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and end the detection;
S2042, if k mpp >0, reading the current photovoltaic power instruction value p pv_ref and judging the value of FlagMPP.
S20421, if FlagMPP <0, let FlagAvF = -1, and assign the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and the detection is finished;
S20422, if FlagMPP >0, reading in the value of FlagAvF, if FlagAvF <0, letting FlagAvF = FlagAvF +1, and assigning the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and ending the detection; if FlagAvF is more than or equal to 0, let u mpp＝upv、impp＝ipv、pmpp＝ppv, flagKno =1, flagAvF = -1, let FlagMPP = -1 at the same time, finally assign the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and end the detection.
Wherein FlagKno flag bits are used for preventing error switching when the MPP is unclear; flagAvF bits are used as a hysteresis function to avoid false detection that may occur when the power characteristic of the photovoltaic array changes with the environment.
S3, adopting a mode switching method of the photovoltaic inverter when the power is insufficient;
Firstly, selecting a corresponding control strategy through mode switching according to the detected photovoltaic working condition. If the load demand power P L is larger than the photovoltaic maximum power P MPP, enabling the photovoltaic inverter to work at a maximum power point through MPPT control; if the load demand power P L is smaller than the photovoltaic maximum power P MPP, the photovoltaic output power command value is obtained in step S102.
Referring to fig. 5, when the power is insufficient, the photovoltaic operation mode switching process specifically includes:
acquiring a reference voltage u pv_ref, and judging whether FlagMPP is larger than 0;
If FlagMPP <0, further judging whether FlagKno is greater than 0, if FlagKno >0, let u pv_ref＝UMPP, flagRToL =1, and ending the handover; if FlagKno <0, let u pv_ref＝upv_ref+cstep, end the handover.
If FlagMPP >0, entering the DC/DC converter power loop to obtain u pv_ref_ac＝ki_dc_p·ppv_err, and judging FlagRToL. If FlagRToL >0, let FlagRToL =0, the photovoltaic port voltage command value remains unchanged, and the switching is finished; if FlagRToL <0, let u pv_ref＝kp_dc_p·ppv_err+upv_ref_ac, end the handover.
Wherein u pv_ref_ac is the DC/DC converter power loop integral value; flagRToL is a photovoltaic working point motion state zone bit, and FlagRToL =1 indicates that the motion state of the photovoltaic working point is just the process of moving from the right side of the MPP to the left side of the MPP; c step is the step parameter as the photovoltaic port voltage increases from 0.
And S4, the pre-stage Boost converter realizes specific photovoltaic power instruction value tracking.
S401, after the photovoltaic power command value in the working mode is determined, obtaining a photovoltaic terminal voltage command value. If the photovoltaic inverter works at the maximum power point, the photovoltaic port voltage control instruction value u in_ref is the photovoltaic voltage corresponding to the maximum power point; if the photovoltaic power command value p pv,ref is smaller than the maximum power, the photovoltaic port voltage control command value u in_ref is obtained through power closed loop control based on PI control, and the calculation formula is as follows:
S402, the duty ratio of the photovoltaic inverter front-stage DC/DC converter is obtained through voltage and current double closed-loop control, and the control strategy of the photovoltaic inverter without energy storage in two modes of P L>PMPP and P L<PMPP is realized.
In still another embodiment of the present invention, a control system of a photovoltaic type without energy storage is provided, which can be used to implement the control method of a photovoltaic type without energy storage described above, and specifically, the control system of a photovoltaic type without energy storage includes a conversion module, a detection module, a judgment module, and a control module.
The conversion module obtains modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed-loop control according to d and q axes reference output voltages u d_ref、uq_ref of the inverter, obtains three-phase modulated waves M a、Mb、Mc of the inverter by utilizing a reference output voltage phase angle theta of the inverter through coordinate transformation, converts the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals, and realizes direct-current side voltage and frequency double droop control by adopting a rear-stage inverter;
The detection module is used for detecting the working mode of the photovoltaic inverter, and obtaining a photovoltaic working mode value FlagMPP and the motion condition of the current photovoltaic working point according to the sampled photovoltaic output voltage u pv and the photovoltaic output power p pv;
The judging module is used for enabling the photovoltaic inverter to work at a maximum power point through MPPT control according to the motion condition of the current photovoltaic working point obtained by the detecting module if the load demand power P L is larger than the photovoltaic maximum power P MPP, and taking the photovoltaic port voltage control instruction value u pv_ref as the photovoltaic output voltage corresponding to the maximum power point; if the load demand power P L is smaller than the photovoltaic maximum power P MPP, switching the working mode, obtaining photovoltaic output power P pv and a photovoltaic working mode value Flag according to the command value P pv,ref of the photovoltaic array output power, and calculating a photovoltaic port voltage control command value u pv_ref as a photovoltaic output voltage corresponding to a maximum power point;
The control module is used for realizing the control strategy of the energy-storage-free photovoltaic inverter in two modes of load demand power P L being larger than photovoltaic maximum power P MPP and load demand power P L being smaller than photovoltaic maximum power P MPP by utilizing the PWM duty ratio signal obtained by the conversion module according to the photovoltaic output voltage u pv and the photovoltaic port voltage control command value u pv_ref corresponding to the maximum power point obtained by the judging module.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In PLECS, a two-machine parallel simulation model as shown in fig. 1 is built for testing the present invention. The power deficiency caused by power disturbances on both sides of the source load can be modeled by changes in the photovoltaic characteristics or the load. Wherein the maximum power of the PV1 photovoltaic array is reduced and increased at 2s and 4s respectively, loading and unloading are performed at 6s and 8s respectively, and the simulation result is shown in FIG. 6.
Before 2s, the two photovoltaic inverters can stably support the alternating current bus and supply power to a load, and the load power is distributed through the sagging coefficient, and in the simulation, the distributed power is 7.1kW because the sagging coefficient of the two inverters is the same. The MPP power (PV 1 is 11.5kW, and pv2 is 23 kW) is sufficient to satisfy the distributed power of each inverter, and as shown in fig. 6 (a) and 6 (d), the output power and voltage are stable, and meet the design requirements.
At 2s, a change in output characteristics of the photovoltaic array was employed. The maximum power of PV1 is reduced from 11.52kW to 4.5kW, which is less than its distributed power of 7.2kW, resulting in a power shortage. This condition may cause a mode detection failure because the power at the same voltage point is different after the characteristic curve is changed, but this problem is solved by the failure detection method. The inverter PV1 is rapidly switched to MPP mode, the insufficient power being compensated by PV 2. The PV1 operates in the MPP mode, in which the photovoltaic terminal voltage is the maximum value after the characteristic change, and the output power is different from the command value, as shown in fig. 6 (c) and 6 (f). Fig. 6 (a), 6 (b), and 6 (d) show simulation waveforms of power, frequency, and dc side voltage of the photovoltaic inverter during switching, which can all reach stable values quickly. And 4s, the maximum power of the PV1 photovoltaic array is increased from 4.5kW to 11.52kW, 7.2kW distributed by the load power is met again, and the normal working state is returned. And between 4s and 6s, the two photovoltaic inverters stably operate in a normal state.
At 6s the load increases and the maximum power of PV1 (11.5 Kw) cannot meet the split power (16.1 Kw). Therefore, inverter PV1 operates in MPP mode and inverter PV2 provides the remaining power of PV 1. The specific procedure first detects this situation and changes the flag bit using the mode detection method, and then the inverter PV1 operates in the MPP mode using the mode switching manner described above. As can be seen from the simulation result in fig. 6, the photovoltaic inverter can smoothly switch to the MPP mode, and no disturbance is introduced during switching. And 8s, load is reduced, the power meets the requirement of the PV1 again, and the photovoltaic inverter returns to the normal running state after detecting that the load power is reduced.
In summary, in the method and system for controlling the photovoltaic voltage without energy storage, in the island micro-grid, the photovoltaic inverter can realize reasonable power distribution for each inverter according to the load demand and the capacity of the inverter, and can actively adjust the voltage and the frequency of the alternating current bus. The photovoltaic mode detection and working mode switching strategy can well cope with power disturbance on the source side and power disturbance on the load side caused by photovoltaic randomness, smooth mode switching can be realized when the photovoltaic power is insufficient, and the shortage power can be borne by other photovoltaic inverters in the parallel system, so that the flexibility of the photovoltaic inverters in the photovoltaic micro-grid is improved, and the reliability of the photovoltaic inverters in future new energy application is improved.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. The energy-storage-free photovoltaic voltage type control method is characterized by comprising the following steps of:
s1, according to d and q axis reference output voltages u d_ref、uq_ref of an inverter, obtaining modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed loop control, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing a reference output voltage phase angle theta of the inverter through coordinate transformation, converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals, and adopting a rear-stage inverter to realize double droop control of direct-current side voltage and frequency;
S2, detecting a working mode of the photovoltaic inverter, and obtaining a working mode value FlagMPP of the photovoltaic and the motion condition of a current photovoltaic working point according to the sampled photovoltaic output voltage u pv and the photovoltaic output power p pv;
S3, according to the motion condition of the current photovoltaic working point obtained in the step S2, if the load demand power P L is larger than the photovoltaic maximum power P MPP, enabling the photovoltaic inverter to work at the maximum power point through MPPT control, and taking the photovoltaic port voltage control command value u pv_ref as the photovoltaic output voltage corresponding to the maximum power point; if the load demand power P L is smaller than the photovoltaic maximum power P MPP, switching the working mode, obtaining photovoltaic output power P pv and a photovoltaic working mode value Flag according to the command value P pv,ref of the photovoltaic array output power, and calculating a photovoltaic port voltage control command value u pv_ref as a photovoltaic output voltage corresponding to a maximum power point;
And S4, according to the photovoltaic output voltage u pv and the photovoltaic port voltage control command value u pv_ref corresponding to the maximum power point obtained in the step S3, using the PWM duty ratio signal obtained in the step S1 to realize the control strategy of the energy-storage-free photovoltaic inverter in two modes that the load demand power P L is larger than the photovoltaic maximum power P MPP and the load demand power P L is smaller than the photovoltaic maximum power P MPP.
2. The method of claim 1, wherein step S1 is specifically:
S101, determining an inverter direct current side voltage reference value U 0, a sagging coefficient k d, virtual inertia J, a synchronous angular frequency w ref and an inverter direct current side capacitor C 0, and calculating a relation coefficient G u between the input power of the photovoltaic array to the inverter and the inverter direct current side voltage and a relation coefficient G w between the inverter direct current side voltage and the output frequency according to the relation coefficient;
S102, obtaining an inverter direct current side voltage reference value U 0 and a sampling inverter direct current side voltage U 0, differentiating U 0 and U 0, and calculating to obtain a photovoltaic array output power instruction value p pv_ref and an inverter reference output voltage phase angle theta by using a relation coefficient G u between the input power of a photovoltaic array to the inverter and the inverter direct current side voltage and a relation coefficient G w between the inverter direct current side voltage and the output frequency;
s103, sampling the output voltage u abc of an inverter port, outputting the current i abc, respectively obtaining the voltage u d、uq and the current i d、iq of d and Q axes through coordinate transformation, and then calculating to obtain the real-time output reactive power Q of the inverter;
S104, calculating to obtain d and Q-axis output reference voltages U d_ref、uq_ref of the inverter according to reactive power Q, sagging coefficient k d, rated voltage amplitude U of an alternating current bus of the inverter and a virtual impedance link;
S105, obtaining d and q axis reference output voltages u d_ref、uq_ref of the inverter, obtaining modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed loop control, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing the phase angle theta of the reference output voltages of the inverter obtained in the step S104 through coordinate transformation, and converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals.
3. The method according to claim 2, wherein in step S104, the inverter d, q-axis output reference voltages u d_ref、uq_ref are:
Wherein L v is virtual impedance, U is rated voltage amplitude of an alternating current bus of the inverter, Q is reactive power, k d is sagging coefficient, w ref is synchronous angular frequency, and i d、iq is value of output current of the inverter under dq synchronous rotation coordinate system.
4. The method according to claim 2, wherein in step S105, the PWM duty cycle signal is:
Wherein M a、Mb、Mc is an inverter three-phase modulation wave, θ is M d、Mq, and a modulation command value is generated by the d-axis current inner loop.
5. The method according to claim 1, wherein in step S2, the operating mode value FlagMPP of the photovoltaic is specifically:
wherein u old and p old are the photovoltaic port voltage and the photovoltaic power at the previous moment, u pv is the output voltage of the sampled photovoltaic, and p pv is the photovoltaic output power.
6. The method for controlling a photovoltaic inverter without energy storage according to claim 5, wherein the detecting the operation mode of the photovoltaic inverter is specifically:
S201, sampling a photovoltaic system to obtain output voltage u pv and current i pv of a current photovoltaic array, reading light Fu Duankou voltage u old and photovoltaic output power p old at the last moment of the photovoltaic system, and calculating to obtain output power p pv of the current photovoltaic array;
S202, judging whether u pv is larger than 5, if u pv is smaller than 5, judging that the photovoltaic inverter works at the left side of MPP at the moment, namely FlagMPP = -1, assigning the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and ending detection; if u pv >5, go to step S203;
S203, judging whether Deltau= |u pv-uold | is larger than 5, and if Deltau <5, directly cutting out of judgment; if Δu >5, go to step S204;
S204, judging whether k mpp＝(upv-uold)·(ppv-pold) is larger than 0; if k mpp is less than 0, continuing to judge the value of FlagMPP; if k mpp >0, the current photovoltaic power instruction value p pv_ref is read in, and the value of FlagMPP is judged.
7. The method according to claim 6, wherein in step S204, if k mpp <0, when FlagMPP >0, flagAvF = -1 is given, and the current light Fu Duankou voltage u pv and the photovoltaic output power p pv are assigned to u old and p old, and the detection is completed; when FlagMPP is less than 0, reading in the value of FlagAvF, when FlagAvF is less than 0, making FlagAvF = FlagAvF +1, and assigning the current light Fu Duankou voltage u pv and the photovoltaic output power p pv to u old and p old, and ending the detection; when FlagAvF is more than or equal to 0, let u mpp＝upv、impp＝ipv、pmpp＝ppv, flagKno =1, flagAvF = -1, let FlagMPP =1 at the same time, finally assign the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and end the detection;
If k mpp >0, when FlagMPP is less than 0, flagAvF = -1 is given, the current light Fu Duankou voltage u pv and the photovoltaic output power p pv are assigned to u old and p old, and the detection is finished; when FlagMPP >0, reading in the value of FlagAvF, if FlagAvF <0, making FlagAvF = FlagAvF +1, and assigning the current light Fu Duankou voltage u pv and the current photovoltaic output power p pv to u old and p old, and ending the detection; when FlagAvF is more than or equal to 0, let u mpp＝upv、impp＝ipv、pmpp＝ppv, flagKno =1, flagAvF = -1, let FlagMPP = -1 at the same time, finally assign the current light Fu Duankou voltage u pv and photovoltaic output power p pv to u old and p old, and end the detection.
8. The method of claim 1, wherein step S3 is specifically:
acquiring a reference voltage u pv_ref, and judging whether a working mode value FlagMPP of the photovoltaic is larger than 0;
If FlagMPP <0, judging whether the error switching flag bit FlagKno is greater than 0, if FlagKno >0, enabling u pv_ref＝UMPP,UMPP to be the voltage corresponding to the photovoltaic maximum power point, and enabling the photovoltaic working point movement state flag bit FlagRToL =1, and ending switching; if FlagKno <0, let u pv_ref＝upv_ref+cstep,cstep be the step parameter when the photovoltaic port voltage increases from 0, and the switching is finished;
If FlagMPP is more than 0, entering a DC/DC converter power loop to obtain a DC/DC converter power loop integral value u pv_ref_ac＝ki_dc_p·ppv_err,ki_dc_p as a power loop integral coefficient, and p pv_err as an error value between reference power and actual power, and judging FlagRToL; if FlagRToL >0, let FlagRToL =0, the photovoltaic port voltage command value remains unchanged, and the switching is finished; if FlagRToL <0, let u pv_ref＝kp_dc_p·ppv_err+upv_ref_ac,upv_ref_ac be the output value of the power loop integral term, k p_dc_p be the power loop proportional control coefficient, and the handover is completed.
9. The method according to claim 1, wherein in step S4, the photovoltaic port voltage control command value u in_ref is specifically:
Wherein U MPP is the voltage corresponding to the maximum power point of the photovoltaic, k p_dc_p is the value of the proportional controller of the PI regulator of the power loop, k i_dc_p is the value of the integral controller of the PI regulator of the power loop, s is the integral link, p pv is the output power of the photovoltaic, and FlagMPP is the value of the working mode of the photovoltaic.
10. A non-energy storage photovoltaic voltage type control system, comprising:
The conversion module is used for obtaining modulated waves M d、Mq under d and q axes by utilizing voltage and current double closed-loop control according to d and q axis reference output voltages u d_ref、uq_ref of the inverter, obtaining three-phase modulated waves M a、Mb、Mc of the inverter by utilizing a reference output voltage phase angle theta of the inverter through coordinate transformation, converting the three-phase modulated waves M a、Mb、Mc into PWM duty ratio signals, and realizing double droop control of direct-current side voltage and frequency by adopting a rear-stage inverter;
The detection module is used for detecting the working mode of the photovoltaic inverter, and obtaining a photovoltaic working mode value FlagMPP and the motion condition of the current photovoltaic working point according to the sampled photovoltaic output voltage u pv and the photovoltaic output power p pv;
The judging module is used for enabling the photovoltaic inverter to work at a maximum power point through MPPT control according to the motion condition of the current photovoltaic working point obtained by the detecting module if the load demand power P L is larger than the photovoltaic maximum power P MPP, and taking the photovoltaic port voltage control instruction value u pv_ref as the photovoltaic output voltage corresponding to the maximum power point; if the load demand power P L is smaller than the photovoltaic maximum power P MPP, switching the working mode, obtaining photovoltaic output power P pv and a photovoltaic working mode value Flag according to the command value P pv,ref of the photovoltaic array output power, and calculating a photovoltaic port voltage control command value u pv_ref as a photovoltaic output voltage corresponding to a maximum power point;
The control module is used for realizing the control strategy of the energy-storage-free photovoltaic inverter in two modes of load demand power P L being larger than photovoltaic maximum power P MPP and load demand power P L being smaller than photovoltaic maximum power P MPP by utilizing the PWM duty ratio signal obtained by the conversion module according to the photovoltaic output voltage u pv and the photovoltaic port voltage control command value u pv_ref corresponding to the maximum power point obtained by the judging module.
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