CN117498429A - Photovoltaic inverter control method and system based on virtual synchronous generator - Google Patents
Photovoltaic inverter control method and system based on virtual synchronous generator 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
- H02J3/38—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
- 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
- H02J3/38—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
- H02J3/48—Controlling the sharing of the in-phase component
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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
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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 renewable new energy source photovoltaic power generation grid-connected control, and discloses a photovoltaic inverter control method and system based on a virtual synchronous generator; the photovoltaic inverter control method comprises the following steps: based on the output power of the direct current side, obtaining an active power reference value through the self-adaptive fuzzy PI controller; calculating to obtain three-phase reference voltage based on the virtual electromotive force phase angle and the virtual electromotive force amplitude; and controlling the photovoltaic inverter based on the obtained three-phase reference voltage. According to the technical scheme provided by the invention, the voltage stability of the direct current bus can be maintained while solar energy is fully utilized under the condition of no energy storage equipment; in addition, the whole system performance can be improved by changing the controller algorithm in the original control system without increasing hardware cost.
Description
Technical Field
The invention belongs to the technical field of renewable new energy source photovoltaic power generation grid-connected control, and particularly relates to a photovoltaic inverter control method and system based on a virtual synchronous generator.
Background
At present, a large amount of intermittent new energy power generation systems such as solar energy, wind energy and the like are built in a large amount, and new energy is connected to a power grid through a power electronic converter; the intermittent new energy sources do not have inertia of the traditional generator, and the intermittent new energy sources bring great challenges to the stability of the power grid. The Virtual Synchronous Generator (VSG) technology can provide external characteristics similar to those of a synchronous generator for an inverter, and can improve the stability of new energy access to a power grid, and has been receiving attention in recent years.
The photovoltaic power generation system generally adopts a maximum power tracking (MPPT) strategy in a pre-stage DC-DC conversion stage so as to fully utilize sunlight resources; therefore, the photovoltaic panel output power varies with changes in solar conditions. However, when the conventional VSG adopts a constant active reference value and the fluctuation of the output power of the photovoltaic is not matched with the active reference value of the VSG, the voltage of the dc bus is greatly fluctuated, even unstable, when the photovoltaic inverter is controlled based on the last conventional Virtual Synchronous Generator (VSG) technology, which is unfavorable for the stable operation of the system.
In the prior art, two methods are generally adopted to solve the problems; the first method is to add energy storage equipment, and control the charge and discharge of the energy storage equipment when the photovoltaic power fluctuates so as to stabilize the voltage of the direct current bus; the second method is to discard MPPT and match the VSG strategy at the back end by adopting a mode of constant output power of the solar panel, and the mode enables the solar cell to work in a limited power state, so that the light energy resource cannot be fully utilized.
In summary, in order to maintain the voltage stability of the dc bus, a new control strategy for the photovoltaic inverter is needed.
Disclosure of Invention
The invention aims to provide a photovoltaic inverter control method and system based on a virtual synchronous generator, which are used for solving one or more technical problems. According to the technical scheme provided by the invention, the voltage stability of the direct current bus can be maintained while solar energy is fully utilized under the condition of no energy storage equipment; in addition, the whole system performance can be improved by changing the controller algorithm in the original control system without increasing hardware cost.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a photovoltaic inverter control method based on a virtual synchronous generator, which comprises the following steps:
obtaining direct current bus parameters; the direct current bus parameters comprise output current, output voltage, filter inductance current, network access current, capacitance voltage and power grid voltage;
calculating to obtain output power of the direct current side based on the output current and the output voltage; based on the output power of the direct current side, an active power reference value is obtained through a self-adaptive fuzzy PI controller;
calculating to obtain three-phase reference voltage based on the virtual electromotive force phase angle and the virtual electromotive force amplitude; the virtual electromotive force phase angle is obtained by inputting the difference value between the active power reference value and the active power actually output by the inverter into an active-frequency control loop; the virtual electromotive force amplitude is obtained by inputting the difference value between the rated phase voltage effective value and the capacitor voltage effective value of the power grid and the difference value between the reactive power reference value and the reactive power actually output by the inverter into a reactive-voltage control loop; the capacitance voltage effective value and the power grid rated phase voltage effective value are obtained based on capacitance voltage and power grid voltage calculation; the actual output active power and reactive power of the inverter are obtained by calculation based on the effective values of the filter inductance current, the network access current and the capacitor voltage and the effective value of the rated phase voltage of the power grid;
and controlling the photovoltaic inverter based on the obtained three-phase reference voltage.
A further improvement of the method of the invention is that, in the step of obtaining the active power reference value by the adaptive fuzzy PI controller based on the output power of the dc side,
the active power reference value is obtained by adding the output power of the direct current bus and an active power reference adjustment value;
the active power reference adjustment value is obtained by the deviation e through the self-adaptive fuzzy PI controller; the deviation e is obtained by subtracting the direct current bus voltage reference value from the direct current bus voltage actual value.
A further improvement of the method of the invention is that the expression of the adaptive fuzzy PI controller is that,
ΔP＝K P e+K I ∫e；
wherein, delta P is the active power reference adjustment value; k (K) P To gain in proportion to the current time, K I For the integral gain at the current time, +.;
wherein, parameter K P And K I The updated equation of (c) is that,
wherein K is I0 For the integral gain at the previous moment, K P0 Is the proportional gain of the previous moment; ΔK I Delta K is the variation of integral gain P Is the change of proportional gain, ΔK I And DeltaK P Obtained by a fuzzy reasoning system.
A further improvement of the method of the invention is that, in the fuzzy inference system,
the input variables are the error e and the derivative e of the error c The output variable is DeltaK P And DeltaK I ；
Input variables e, e c And output variable ΔK P 、ΔK I Respectively dividing into 7 fuzzy variables which are represented as { PB, PM, PS, ZO, NS, NM, NB }; the membership functions are all triangular functions; the domains of the input and output variables are denoted e E [ -100, respectively]，e c ∈[-1000,1000]，ΔK P ∈[-75,75]，ΔK I ∈[-50,50]；
The fuzzy control rule aims to eliminate errors as soon as possible and realize stable operation of the system;
fuzzy reasoning is carried out by using a Mamdani reasoning algorithm to obtain a fuzzy output quantity; the defuzzification adopts a gravity center method to obtain delta K P And DeltaK I Is a clear value of (c).
The method is further improved in that the fuzzy control rule is determined according to the magnitude of an error e;
wherein when the error e is positive and gradually increases, ΔK p The value is negative and gradually decreases, delta K I The value is positive and gradually increases; when the error e is negative and gradually decreases, ΔK p The value is positive and gradually increases, delta K I The value takes a negative and gradually decreases.
A further improvement of the method of the invention is that the active-frequency control loop is represented as,
wherein θ is a virtual electromotive force phase angle; omega and omega n Respectively, are electric networksIs set to the actual angular frequency and the nominal angular frequency; p (P) ref Is an active power reference value; p is the active power actually output by the inverter; d (D) p Is a damping coefficient; j is the virtual moment of inertia.
A further improvement of the method of the present invention is that the calculated expression of the virtual electromotive force amplitude is,
wherein E is a virtual electromotive force amplitude; k is the reactive power integral coefficient; c is an integral function; q (Q) ref A set reactive power reference value; q is the reactive power actually output by the inverter; d (D) q Is the sag factor of VSG; u (U) N The method is a power grid rated phase voltage effective value; u is the effective value of the capacitor voltage.
The method is further improved in that the step of calculating the three-phase reference voltage based on the virtual electromotive force phase angle and the virtual electromotive force amplitude is that,
and multiplying the virtual electromotive force phase angle output by the front stage by the virtual electromotive force amplitude to obtain the three-phase reference voltage.
A further improvement of the method of the present invention is that the step of controlling the photovoltaic inverter based on the obtained three-phase reference voltage comprises:
and inputting the obtained three-phase reference voltage into an inverter voltage and current double closed loop, and then performing SPWM (sinusoidal Pulse width modulation) to obtain a three-phase full-bridge driving Pulse of the inverter so as to realize the control of the inverter.
The invention provides a photovoltaic inverter control system based on a virtual synchronous generator, which comprises the following components:
the parameter acquisition module is used for acquiring parameters of the direct current bus; the direct current bus parameters comprise output current, output voltage, filter inductance current, network access current, capacitance voltage and power grid voltage;
the active power reference value acquisition module is used for calculating and acquiring the output power of the direct current side based on the output current and the output voltage; based on the output power of the direct current side, an active power reference value is obtained through a self-adaptive fuzzy PI controller;
the three-phase reference voltage acquisition module is used for calculating and obtaining three-phase reference voltages based on the virtual electromotive force phase angle and the virtual electromotive force amplitude; the virtual electromotive force phase angle is obtained by inputting the difference value between the active power reference value and the active power actually output by the inverter into an active-frequency control loop; the virtual electromotive force amplitude is obtained by inputting the difference value between the rated phase voltage effective value and the capacitor voltage effective value of the power grid and the difference value between the reactive power reference value and the reactive power actually output by the inverter into a reactive-voltage control loop; the capacitance voltage effective value and the power grid rated phase voltage effective value are obtained based on capacitance voltage and power grid voltage calculation; the actual output active power and reactive power of the inverter are obtained by calculation based on the effective values of the filter inductance current, the network access current and the capacitor voltage and the effective value of the rated phase voltage of the power grid;
and the control module is used for controlling the photovoltaic inverter based on the obtained three-phase reference voltage.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a photovoltaic inverter control method based on a virtual synchronous generator, which discloses a fuzzy PI-based photovoltaic power generation VSG active reference value adjustment scheme and solves the technical problem of unstable system operation caused by direct current bus voltage fluctuation caused by the change of output of a photovoltaic cell panel in the existing VSG technology. The method is particularly explanatory, the active reference value of the VSG technology is changed to adapt to the output of the photovoltaic cell panel, the active reference value is changed by adopting a self-adaptive fuzzy PI strategy, and the voltage stability of the direct current bus can be maintained while solar energy is fully utilized under the condition of no energy storage equipment; the technical scheme provided by the invention has the advantages that the hardware cost is not required to be increased, the performance of the whole system can be improved by only changing the controller algorithm in the original control system, and the method has a good application prospect.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description of the embodiments or the drawings used in the description of the prior art will make a brief description; it will be apparent to those of ordinary skill in the art that the drawings in the following description are of some embodiments of the invention and that other drawings may be derived from them without undue effort.
Fig. 1 is a schematic flow chart of a photovoltaic inverter control method based on a virtual synchronous generator according to an embodiment of the present invention;
FIG. 2 is a schematic block diagram of an overall control system on which the technical solution depends in an embodiment of the present invention;
FIG. 3 is a schematic block diagram of adaptive fuzzy PI control employed in an embodiment of the present invention;
FIG. 4 is a schematic diagram of a fuzzy membership function corresponding to e employed in an embodiment of the present invention;
FIG. 5 shows the correspondence e employed in an embodiment of the present invention c Is a fuzzy membership function diagram;
FIG. 6 shows the corresponding ΔK employed in an embodiment of the present invention p Is a fuzzy membership function diagram;
FIG. 7 shows the corresponding ΔK employed in an embodiment of the present invention I Is a fuzzy membership function diagram;
FIG. 8 is a schematic block diagram of a voltage-current dual closed-loop control employed in an embodiment of the present invention;
FIG. 9 is a schematic block diagram of SPWM modulation employed in an embodiment of the present invention;
FIG. 10 is a graph showing the variation of the active power output under a set operating condition according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of a voltage variation curve of a DC bus under a set working condition in an embodiment of the present invention;
FIG. 12 is a schematic diagram showing the comparison of the DC bus voltage under the set working condition of the method according to the embodiment of the present invention and the conventional PI method;
fig. 13 is a schematic diagram of a photovoltaic inverter control system based on a virtual synchronous generator according to an embodiment of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in 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 only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the attached drawing figures:
referring to fig. 1, the method for controlling a photovoltaic inverter based on a virtual synchronous generator provided by the embodiment of the invention includes the following steps:
step 1, obtaining direct current bus parameters; wherein the DC bus parameters comprise output current I dc Output voltage U dc The method comprises the steps of carrying out a first treatment on the surface of the Filter inductor current I La 、I Lb 、I Lc The method comprises the steps of carrying out a first treatment on the surface of the Network current I a 、I b 、I c Capacitor voltage U a 、U b 、U c The method comprises the steps of carrying out a first treatment on the surface of the Grid voltage U ga 、U gb 、U gc The method comprises the steps of carrying out a first treatment on the surface of the In particular exemplary, the data may be collected by a current sensor and a voltage sensorAcquiring the direct current bus parameters;
step 2, based on the output current I dc Output voltage U dc Calculating to obtain output power P of DC side pv The method comprises the steps of carrying out a first treatment on the surface of the Based on the output power P of the DC side pv Active power reference value P is obtained through self-adaptive fuzzy PI controller ref ；
Step 3, calculating to obtain a three-phase reference voltage U based on the virtual electromotive force phase angle theta and the virtual electromotive force amplitude E * abc The method comprises the steps of carrying out a first treatment on the surface of the Wherein the virtual electromotive force phase angle theta is obtained by comparing the active power reference value P ref The difference value of the active power P actually output by the inverter is input into an active-frequency control loop to obtain; the virtual electromotive force amplitude E is used for effectively measuring the rated phase voltage U of the power grid N Difference from the effective value U of the capacitor voltage and the reactive power reference value Q ref The difference value of the reactive power Q actually output by the inverter is input into a reactive-voltage control loop to obtain; capacitor voltage effective value U and power grid rated phase voltage effective value U N Based on capacitance voltage U a 、U b 、U c Grid voltage U ga 、U gb 、U gc Calculating to obtain; active power P and reactive power Q actually output by the inverter based on filter inductance current I La 、I Lb 、I Lc Network access current I a 、I b 、I c Capacitor voltage effective value U and power grid rated phase voltage effective value U N Calculating to obtain;
step 4, based on the three-phase reference voltage U obtained in step 3 * abc Controlling the photovoltaic inverter; in particular, the three-phase reference voltage U obtained in the step 3 can be exemplified * abc After the voltage and current double closed loops of the inverter are input, SPWM (sinusoidal Pulse width modulation) is performed to obtain three-phase full-bridge driving Pulse of the inverter, and control of the photovoltaic inverter is achieved.
Aiming at the problem of unstable direct-current side voltage in distributed photovoltaic power generation, the embodiment of the invention provides a VSG control for giving an active power reference value by adopting a self-adaptive fuzzy PI controller according to the difference value between a direct-current reference voltage and an actually measured direct-current voltage. When solar radiation is large, the method realizes that the direct current bus voltage is stabilized while avoiding complex PI parameter adjustment under the conditions that the output power of the photovoltaic module is not limited and energy storage equipment is not needed, improves the stability of constant active reference value VSG control, and simultaneously has smaller overshoot and faster response speed compared with the traditional PI control. The technical scheme of the embodiment of the invention can effectively ensure the voltage stability of the direct current side based on VSG control.
The core invention point of the technical proposal provided by the embodiment of the invention is that,
the voltage of the direct-current bus is stabilized by adjusting the active power reference value, no additional energy storage equipment is needed, and the control stability of the photovoltaic power generation VSG is improved under the condition of not increasing the complexity and cost of system hardware; the method allows the photovoltaic module to always keep the maximum power tracking control mode, thereby ensuring the high-efficiency utilization of solar energy; in addition, the performance of the PI controller is improved by utilizing fuzzy inference parameter adjustment, so that the complex PI parameter adjustment is avoided, and meanwhile, the response performance of the system is improved.
Referring to fig. 2, fig. 2 shows a block diagram of a photovoltaic power generation VSG control system on which the method according to the embodiment of the present invention depends, where the block diagram includes a main circuit block diagram and a control system block diagram, and the two parts are connected by a three-phase full-bridge driving Pulse provided by the control system, where one side of the main circuit is connected to the output of the photovoltaic power generation DC-DC converter, U dc Other major components are dc bus voltage: the direct-current voltage sensor 1, the direct-current sensor 2, the direct-current bus capacitor 3, the direct-current side power calculation module 4, the inverter main circuit 5, the filter inductor 6, the filter inductor current sensor 7, the capacitor voltage sensor 8, the filter capacitor 9, the network-access current sensor 10, the power grid voltage sensor 11, the line impedance 12, the large power grid 13, (two) effective value calculation modules 14, the power calculation module 15, the active power reference value calculation module 16, the active-frequency control loop 17, the reactive-voltage control loop 18, the reference voltage calculation module 19, the voltage-current double closed-loop control module 20 and the SPWM modulation module 21.
The control principle of the technical scheme of the embodiment of the invention comprises the following steps: respectively byThe direct-current voltage sensor and the direct-current sensor collect output voltage signals U of a direct-current bus dc And outputting a DC signal I dc Sending the power into a DC side power calculation module to calculate and obtain the output power P of a DC bus pv The method comprises the steps of carrying out a first treatment on the surface of the Reference value U of DC bus voltage dcref And the actual value U of the DC bus voltage dc Comparing and calculating an active power reference value P through an adaptive fuzzy PI controller ref The method comprises the steps of carrying out a first treatment on the surface of the Collecting capacitance voltage U a 、U b 、U c And network access current I a 、I b 、I c The capacitor voltage U a 、U b 、U c With the network voltage U ga 、U gb 、U gc Calculating effective values U of capacitor voltage and grid voltage by an effective value calculation (RMS) module respectively N The capacitor voltage U a 、U b 、U c And network access current I a 、I b 、I c Inputting an alternating current power calculation module to obtain active power P and reactive power Q actually output by an inverter; reference value P of active power ref And the active power P actually output by the inverter is sent to an active-frequency control module to obtain a virtual electromotive force phase angle theta; the capacitance voltage effective value U and the grid voltage effective value U are combined N Sending the virtual electromotive force to a reactive-voltage control module to obtain a virtual electromotive force amplitude E; then the virtual electromotive force amplitude E and the virtual electromotive force phase angle theta are sent into a reference voltage calculation module to obtain a three-phase voltage reference voltage U * abc And sending the Pulse to a voltage-current double closed loop module and an SPWM (sinusoidal Pulse width modulation) module to obtain the three-phase full-bridge driving Pulse of the inverter.
The core part of the technical scheme of the embodiment of the invention is that the voltage reference value U of the direct current bus is calculated dcref And the actual value U of the DC bus voltage dc Comparing and calculating an active power reference value P through an adaptive fuzzy PI controller ref 。
The control method of the embodiment of the invention can be implemented according to the following steps based on the structural principle:
step 1, respectively acquiring output current I of a direct current bus through a current sensor and a voltage sensor dc Output voltage U dc Filter inductor current I La 、I Lb 、I Lc Network access current I a 、I b 、I c Capacitor voltage U a 、U b 、U c Grid voltage U ga 、U gb 、U gc ；
Step 2, calculating the output power P of the DC side pv Active power reference value P is obtained through self-adaptive fuzzy PI controller ref The method comprises the steps of carrying out a first treatment on the surface of the Wherein the active power reference value P ref The adaptive fuzzy PI controller used for the calculation of (a) can be seen in fig. 3; active power reference value P ref From P pv And ΔP are added to obtain, P pv Is the output power of the DC bus, delta P is the reference adjustment value of active power, and the reference value U of DC bus voltage dcref And the actual value U of the DC bus voltage dc The subtracted deviation e is obtained through a PI controller;
the PI controller expression is as follows
ΔP＝K P e+K I ∫e (1)
Wherein K is P Is the proportional gain at the current time, K I For the integral gain at the current instant, +..
Parameter K of PI controller P And K I The updated equation of (c) is that,
wherein K is I0 For the integral gain at the previous moment, K P0 Is the proportional gain of the previous moment; ΔK I Delta K is the variation of integral gain P Is the change of proportional gain, ΔK I And DeltaK P Obtained by a fuzzy reasoning system.
In the embodiment of the invention, according to the principle of a fuzzy inference system, the input error e and the derivative e of the error of the fuzzy inference system are obtained c Output delta K of fuzzy inference system P And DeltaK I The four variables (2 inputs, 2 outputs)Are divided into 7 fuzzy variables, given by { PB, PM, PS, ZO, NS, NM, NB }, respectively expressed as: positive large (PB), median (PM), positive Small (PS), zero (ZO), negative Small (NS), negative Median (NM), negative large (NB); the membership functions are trigonometric functions, but the domains are different, and are respectively input e E < -100 > and 100 [ -100 ]]，e c ∈[-1000,1000]Output DeltaK P ∈[-75,75]，ΔK I ∈[-50,50]The method comprises the steps of carrying out a first treatment on the surface of the In a specific example, the membership functions of the four variables are shown in fig. 4, 5, 6, and 7, respectively.
The establishment of the fuzzy control rule is based on expert experience to eliminate errors as soon as possible, so as to realize stable operation of the system. Wherein it is generally determined according to the magnitude of the error e. When the error e is positive and gradually increases, ΔK p The value is negative and gradually decreases, delta K I The value is positive and gradually increases; when the error e is negative and gradually decreases, ΔK p The value is positive and gradually increases, delta K I The value takes a negative and gradually decreases. Adjusting according to the rule and actual engineering experience to obtain delta K P 、ΔK I The fuzzy rules of (a) are shown in tables 1 and 2.
TABLE 1 DeltaK P Fuzzy control rule table
TABLE 2 DeltaK I Fuzzy control rule table
Fuzzy reasoning is carried out by using a Mamdani reasoning algorithm to obtain a fuzzy output quantity; the deblurring is performed by adopting a gravity center method to obtain delta K P And DeltaK I Calculating the update of the proportional gain and the integral gain according to the formula (2) to finish the self-adaption of the parameters of the self-adaption fuzzy PI controllerThe adjustment is needed, and then the adjustment of the VSG active reference value is realized through a PI controller;
step 3, calculating an effective value U of the capacitor voltage and an effective value U of the grid voltage through an effective value calculation module N Calculating the actual active power P and reactive power Q output by the inverter through a power calculation module; by comparing the active power with a reference value P ref The difference value of the active power P actually output by the inverter is input into an active-frequency control loop to obtain a virtual electromotive force phase angle theta; rated phase voltage effective value U of power grid N Difference from the effective value U of the capacitor voltage and the reactive power reference value Q ref The difference value of the actual output reactive power Q of the inverter is input into a reactive-voltage control loop to obtain a virtual electromotive force amplitude E, and a three-phase reference voltage U is obtained through a reference voltage calculation module * abc ，
The virtual synchronous machine active-frequency control model can be expressed as follows:
wherein J is virtual moment of inertia; d (D) p Is a damping coefficient; θ is the virtual electromotive force phase angle, ω and ω n The actual angular frequency and the rated angular frequency of the power grid respectively.
The VSG allows the inverter to have one-time voltage regulation in the grid-connected mode by mimicking the reactive-voltage sag characteristics of the synchronous generator, and obtains the virtual electromotive force amplitude E according to the structural block diagram of the reactive-voltage control link in fig. 2 as follows,
in U N Rated phase voltage effective value, Q for power grid ref For the set reactive power reference value D q K is the reactive power integral coefficient, and ∈is the integral function, corresponding to 1/s in FIG. 2, for the droop coefficient of VSG.
Virtual electromotive force phase angle output through the front stageθ is multiplied by the virtual electromotive force amplitude E to obtain a three-phase reference voltage U * abc The method can be expressed as follows:
step 4, the three-phase reference voltage U obtained in the step three is obtained * abc After voltage and current double closed loops of an inverter are input, SPWM (sinusoidal Pulse width modulation) is carried out to obtain three-phase full-bridge driving Pulse of the inverter, and control of the inverter is realized; in particular exemplary, the input three-phase reference voltage U is first * abc Network current I a 、I b 、I c Capacitor voltage U a 、U b 、U c Filter inductor current I La 、I Lb 、I Lc In the conversion to the dq coordinate system, the conversion formula is shown below,
wherein X represents a variable to be converted, X d 、X q And X a 、X b 、X c Representing the components of the variable to be converted in the d-axis, q-axis and a, b, c-axis, respectively.
The converted reference voltage is U * d 、U * q The capacitance voltage is U d 、U q The filter inductance current is I Ld 、I Lq The network access current is I d 、I q The method comprises the steps of carrying out a first treatment on the surface of the The expressions of the voltage and current double closed-loop control are shown as (7) and (8),
in the method, in the process of the invention,represents integral, k pv And k iv Respectively the proportional coefficient and the integral coefficient, k of the voltage ring PI controller pc And k ic Proportional and integral coefficients, i, of the current loop PI controller, respectively * d 、i * q E is the representation form of the current inner loop reference value under the dq coordinate system * d 、E * q For the representation of the output voltage reference value of the inverter in the dq coordinate system, ω is the actual angular frequency of the grid, C f For filtering capacitance, L f Zero error tracking of the reference voltage and the reference current can be realized through control loops of the voltage outer loop and the current inner loop for filtering the inductance.
Reference value E of output voltage of inverter * d ，E * q Converting into abc coordinate system, wherein the conversion formula is shown in the following formula, and the reference three-phase electromotive force E is obtained by conversion * a ，E * b ，E * c A complete voltage-current double closed loop control is achieved as shown in fig. 8.
Reference value E of output voltage of inverter * a ，E * b ，E * c As the modulated wave and the triangular carrier wave pass through the comparator to obtain the three-phase full-bridge driving Pulse of the inverter, as shown in fig. 9, the three-phase driving Pulse drives three bridge arms respectively, and the driving Pulse of the two switching tubes of the upper bridge arm and the lower bridge arm is a complementary Pulse with protection time delay in specific implementation, and can be controlled by one driving Pulse.
In the embodiment of the invention, in order to verify the control strategy provided by the embodiment of the invention, a model is built on MATLAB/Simulink for simulation verification. The simulation parameters are as follows: the photovoltaic module selects 10 SunPower SPR-305E-WHT-D modules to be connected in seriesThe maximum power point tracking control is adopted, and the direct current bus voltage reference value U is adopted dcref =1500v, net rated phase voltage effective value U N =220V, grid rated frequency f N =50hz, 4mH filter inductance, 10 μf filter capacitance, damping coefficient D p =41, reactive sag factor dq=76, virtual moment of inertia j=3 kg.m2, reactive power integral factor k=0.077;
as shown in fig. 10 and 11, the reference value Q of reactive power is ref Setting to 0, fixing the temperature of the photovoltaic module to 25 ℃, and irradiance at 2 seconds from 1000W/m 2 Suddenly drop to 600W/m 2 Irradiance at 4 seconds is from 600W/m 2 Up to 800W/m 2 Under the working condition of (1), the direct current bus voltage U dc And an output power P change curve; it can be seen from fig. 10 and 11 that the dc bus voltage U is reduced when the photovoltaic output is suddenly reduced dc Will drop briefly and regain balance after a period of time; when the photovoltaic output is excessive, the DC bus voltage U dc Will briefly rise to restore equilibrium after a period of time, consistent with the results of the previous theoretical analysis.
As shown in fig. 12, when the reactive power reference value Qref is set to 0, the temperature of the photovoltaic module is fixed to 25 ℃, and irradiance is suddenly reduced from 600W/m2 to 800W/m2 at 3 seconds, the dc bus voltage Udc of the conventional PI regulator and the adaptive fuzzy PI regulator is simulated in comparison; it can be seen that the dc bus voltage Udc output by the adaptive fuzzy PI regulator has a faster response speed and a lower overshoot than the conventional PI regulator control.
In summary, the embodiment of the invention discloses a fuzzy PI-based photovoltaic VSG power reference adjustment scheme for controlling a photovoltaic inverter, which may include the following implementation steps: 1) Collecting output voltage and output current of a direct current bus, and filtering inductance current, network access current, capacitance voltage and power grid voltage; 2) Calculating output power of a direct current side, and obtaining an active power reference value through a self-adaptive fuzzy PI controller; 3) Calculating effective values of capacitor voltage and grid voltage, and active power and reactive power output by an inverter; obtaining a virtual electromotive force phase angle and a virtual electromotive force amplitude through an active-frequency loop and a reactive-voltage loop, and further synthesizing a three-phase reference voltage; 4) And performing voltage-current double closed loop and SPWM modulation to obtain six paths of switch control pulses for driving the three-phase inverter. According to the technical scheme, the active power reference value of the VSG is adjusted by introducing the self-adaptive fuzzy PI control, and the fluctuation of solar energy is fully utilized under the condition that an energy storage element is not increased and the output power of a solar panel is limited; furthermore, the PI controller parameters are adjusted by the fuzzy rule, so that the response speed is improved, the difficulty in PI parameter adjustment is avoided, and the method is more suitable for distributed photovoltaic power generation.
The following are device embodiments of the present invention that may be used to perform method embodiments of the present invention. For details not disclosed in the apparatus embodiments, please refer to the method embodiments of the present invention.
Referring to fig. 13, in still another embodiment of the present invention, a photovoltaic inverter control system based on a virtual synchronous generator is provided, including:
the parameter acquisition module is used for acquiring parameters of the direct current bus; the direct current bus parameters comprise output current, output voltage, filter inductance current, network access current, capacitance voltage and power grid voltage;
the active power reference value acquisition module is used for calculating and acquiring the output power of the direct current side based on the output current and the output voltage; based on the output power of the direct current side, an active power reference value is obtained through a self-adaptive fuzzy PI controller;
the three-phase reference voltage acquisition module is used for calculating and obtaining three-phase reference voltages based on the virtual electromotive force phase angle and the virtual electromotive force amplitude; the virtual electromotive force phase angle is obtained by inputting the difference value between the active power reference value and the active power actually output by the inverter into an active-frequency control loop; the virtual electromotive force amplitude is obtained by inputting the difference value between the rated phase voltage effective value and the capacitor voltage effective value of the power grid and the difference value between the reactive power reference value and the reactive power actually output by the inverter into a reactive-voltage control loop; the capacitance voltage effective value and the power grid rated phase voltage effective value are obtained based on capacitance voltage and power grid voltage calculation; the actual output active power and reactive power of the inverter are obtained by calculation based on the effective values of the filter inductance current, the network access current and the capacitor voltage and the effective value of the rated phase voltage of the power grid;
and the control module is used for controlling the photovoltaic inverter based on the obtained three-phase reference voltage.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (10)
1. The photovoltaic inverter control method based on the virtual synchronous generator is characterized by comprising the following steps of:
obtaining direct current bus parameters; the direct current bus parameters comprise output current, output voltage, filter inductance current, network access current, capacitance voltage and power grid voltage;
calculating to obtain output power of the direct current side based on the output current and the output voltage; based on the output power of the direct current side, an active power reference value is obtained through a self-adaptive fuzzy PI controller;
calculating to obtain three-phase reference voltage based on the virtual electromotive force phase angle and the virtual electromotive force amplitude; the virtual electromotive force phase angle is obtained by inputting the difference value between the active power reference value and the active power actually output by the inverter into an active-frequency control loop; the virtual electromotive force amplitude is obtained by inputting the difference value between the rated phase voltage effective value and the capacitor voltage effective value of the power grid and the difference value between the reactive power reference value and the reactive power actually output by the inverter into a reactive-voltage control loop; the capacitance voltage effective value and the power grid rated phase voltage effective value are obtained based on capacitance voltage and power grid voltage calculation; the actual output active power and reactive power of the inverter are obtained by calculation based on the effective values of the filter inductance current, the network access current and the capacitor voltage and the effective value of the rated phase voltage of the power grid;
and controlling the photovoltaic inverter based on the obtained three-phase reference voltage.
2. The method according to claim 1, wherein in the step of obtaining an active power reference value by an adaptive fuzzy PI controller based on the output power of the DC side,
the active power reference value is obtained by adding the output power of the direct current bus and an active power reference adjustment value;
the active power reference adjustment value is obtained by the deviation e through the self-adaptive fuzzy PI controller; the deviation e is obtained by subtracting the direct current bus voltage reference value from the direct current bus voltage actual value.
3. The method for controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 2, wherein the adaptive fuzzy PI controller is expressed as,
ΔP＝K P e+K I ∫e；
wherein, delta P is the active power reference adjustment value; k (K) P To gain in proportion to the current time, K I For the integral gain at the current time, +.;
wherein, parameter K P And K I The updated equation of (c) is that,
wherein K is I0 For the integral gain at the previous moment, K P0 Is the proportional gain of the previous moment; ΔK I Delta K is the variation of integral gain P Is the change of proportional gain, ΔK I And DeltaK P Obtained by a fuzzy reasoning system.
4. The method for controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 3, wherein, in the fuzzy inference system,
the input variables are the error e and the derivative e of the error c The output variable is DeltaK P And DeltaK I ；
Input variables e, e c And output variable ΔK P 、ΔK I Respectively dividing into 7 fuzzy variables which are represented as { PB, PM, PS, ZO, NS, NM, NB }; the membership functions are all triangular functions; the domains of the input and output variables are denoted e E [ -100, respectively]，e c ∈[-1000,1000]，ΔK P ∈[-75,75]，ΔK I ∈[-50,50]；
The fuzzy control rule aims to eliminate errors as soon as possible and realize stable operation of the system;
fuzzy reasoning is carried out by using a Mamdani reasoning algorithm to obtain a fuzzy output quantity; the defuzzification adopts a gravity center method to obtain delta K P And DeltaK I Is a clear value of (c).
5. The method for controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 4, wherein the fuzzy control rule is determined according to the magnitude of the error e;
wherein when the error e is positive and gradually increases, ΔK p The value is negative and gradually decreases, delta K I The value is positive and gradually increases; when the error e is negative and gradually decreases, ΔK p The value is positive and gradually increases, delta K I The value takes a negative and gradually decreases.
6. A method of controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 1, wherein the active-frequency control loop is represented as,
wherein θ is a virtual electromotive force phase angle; omega and omega n The actual angular frequency and the rated angular frequency of the power grid are respectively; p (P) ref Is an active power reference value; p is the active power actually output by the inverter; d (D) p Is a damping coefficient; j is the virtual moment of inertia.
7. The method for controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 1, wherein the virtual electromotive force amplitude is calculated by the following expression,
wherein E is a virtual electromotive force amplitude; k is the reactive power integral coefficient; c is an integral function; q (Q) ref A set reactive power reference value; q is the reactive power actually output by the inverter; d (D) q Is the sag factor of VSG; u (U) N The method is a power grid rated phase voltage effective value; u is the effective value of the capacitor voltage.
8. The method for controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 1, wherein the step of calculating a three-phase reference voltage based on a virtual electromotive force phase angle and a virtual electromotive force amplitude is,
and multiplying the virtual electromotive force phase angle output by the front stage by the virtual electromotive force amplitude to obtain the three-phase reference voltage.
9. The method for controlling a photovoltaic inverter based on a virtual synchronous generator according to claim 1, wherein the step of controlling the photovoltaic inverter based on the obtained three-phase reference voltage comprises:
and inputting the obtained three-phase reference voltage into an inverter voltage and current double closed loop, and then performing SPWM (sinusoidal Pulse width modulation) to obtain a three-phase full-bridge driving Pulse of the inverter so as to realize the control of the inverter.
10. A photovoltaic inverter control system based on a virtual synchronous generator, comprising:
the parameter acquisition module is used for acquiring parameters of the direct current bus; the direct current bus parameters comprise output current, output voltage, filter inductance current, network access current, capacitance voltage and power grid voltage;
the active power reference value acquisition module is used for calculating and acquiring the output power of the direct current side based on the output current and the output voltage; based on the output power of the direct current side, an active power reference value is obtained through a self-adaptive fuzzy PI controller;
the three-phase reference voltage acquisition module is used for calculating and obtaining three-phase reference voltages based on the virtual electromotive force phase angle and the virtual electromotive force amplitude; the virtual electromotive force phase angle is obtained by inputting the difference value between the active power reference value and the active power actually output by the inverter into an active-frequency control loop; the virtual electromotive force amplitude is obtained by inputting the difference value between the rated phase voltage effective value and the capacitor voltage effective value of the power grid and the difference value between the reactive power reference value and the reactive power actually output by the inverter into a reactive-voltage control loop; the capacitance voltage effective value and the power grid rated phase voltage effective value are obtained based on capacitance voltage and power grid voltage calculation; the actual output active power and reactive power of the inverter are obtained by calculation based on the effective values of the filter inductance current, the network access current and the capacitor voltage and the effective value of the rated phase voltage of the power grid;
and the control module is used for controlling the photovoltaic inverter based on the obtained three-phase reference voltage.
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