CN109004680B - Wind power plant power control method and system based on energy storage inverter - Google Patents
Wind power plant power control method and system based on energy storage inverter 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
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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
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- 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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention relates to a wind power plant power control method and a system based on an energy storage inverter, belonging to the field of wind power generation control. The wind power plant power control method not only realizes the rapid and smooth fluctuation of the wind power plant power, but also ensures the stable operation of the virtual synchronous generator.
Description
Technical Field
The invention belongs to the field of wind power generation control, and particularly relates to a wind power plant power control method and system based on an energy storage inverter.
Background
In recent years, wind power generation is rapidly developed, and due to the influence of natural conditions, the active output fluctuation of a wind power plant is large, so that the impact on a power grid is serious. In order to reduce the impact, an energy storage inverter (i.e., an energy storage battery system including an energy storage battery, an inverter and a filter) is usually adopted to smooth the output of the wind farm, for example, the smoothing methods can stabilize the wind power grid-connected power fluctuation to a certain extent and reduce the grid-connected impact of the wind farm on the power grid, such as a method for performing adaptive smoothing on the wind power by using a battery energy storage system, which is proposed in chinese patent application with publication number CN 102738817A; however, although the methods can smooth the active output of the wind power plant, the smoothed active output is only reduced in fluctuation degree, and is still uncontrollable, and cannot actively participate in frequency modulation and voltage regulation of the power grid.
In order to enhance the capacity of participating in frequency modulation and voltage regulation of a power grid of a wind power plant while smoothing the output of the wind power plant, Chinese patent with publication number CN102074967B provides 'an energy storage type wind power plant control method with grid-connected characteristic', the method smoothes the output power of the wind power plant by introducing a virtual synchronous generator technology, so that the wind power plant embodies the characteristic of the synchronous generator and participates in frequency modulation and voltage regulation of the power grid, but the control method enables the fluctuating power of the wind power plant to act on the virtual synchronous generator, so that the frequency and the power angle of the virtual synchronous generator are also seriously fluctuated, and the virtual synchronous generator has larger inertia, and the conversion from the mechanical power to the electromagnetic power of the virtual synchronous generator needs a certain response time, so the capacity of smoothing the power fluctuation of the wind power plant.
Specifically, the power frequency controller proposed by the method is shown in fig. 3, and indicates: "for ease of analysis, consider the case where there is no fluctuation in the system load, where f is fN＝50Hz，△P＝0。PNThe method is characterized in that a wind power plant grid-connected power instruction value is also used as a rated active power value of a virtual synchronous generator, the value of the wind power plant grid-connected power instruction value is a value of active power output by the maximum power tracking MPPT control of the wind power plant after low-pass filtering, and power high-frequency components which have large influence on a power grid are filtered. Power instruction value P of energy storage batteryT＝PN-PWTAnd the stabilization of the active power of the wind power plant is realized. "as shown in FIG. 1, PNIs PWTThe output through the low-pass filter, i.e. PWTLow frequency component of middle, and PTIs- (P)WT-PN) I.e. PTIs PWTSubtracting the low frequency component PNThe latter result, namely P in factWTMedium high frequency component and takes negative.
PTIs the mechanical power acting on the virtual synchronous generator, mechanical power PTThe virtual synchronous generator contains high-frequency components, so that the mechanical power acting on a rotor of the virtual synchronous generator is small and large, the corresponding mechanical torque is small and large, the running state of the virtual synchronous generator is unstable, the frequency fluctuates frequently, the frequency of the voltage generated by the virtual synchronous generator is unstable, and the power angle of the virtual synchronous generator is unstable.
Equivalent model of a virtual synchronous generator in grid-connected operation as shown in fig. 2, VSG (virtual synchronous generator) sends outActive power of can be expressed as
The power angle is an included angle between a rotor magnetic field and a stator magnetic field, E is an electromotive force of the virtual synchronous generator, U is a power grid voltage, and X is an equivalent reactance (neglected resistance) from the virtual synchronous generator to a power grid; x is generally fixed and constant, and the grid voltage U is also generally stable, so that the active power generated by the VSG mainly depends on the power angle under the condition that the electromotive force E of the virtual synchronous generator is constant.
After the mechanical power acting on the rotor is increased or decreased, because the virtual synchronous generator rotor has inertia, a longer transition time is needed to enable the rotor to move to a new power angle in an acceleration or deceleration manner, that is, the response speed of the active power generated by the virtual generator to the change of the input mechanical power is slow, and the power angle of the virtual synchronous generator may not change at all when the input mechanical power changes fast, so that the electromagnetic power generated by the virtual synchronous generator cannot change rapidly along with the change of the mechanical power, and the smoothing effect is affected.
And, PNThe MPPT output active power of the wind power plant is the value of the low-pass filter, so that the P is shownNCannot be set manually, but the virtual synchronous generator secondary frequency modulation is adjusted by adjusting PNTherefore, the virtual synchronous generator of the method does not have the secondary frequency modulation capability.
Disclosure of Invention
The invention aims to provide a wind power plant power control method and system based on an energy storage inverter, which are used for solving the problems that the output power effect of a smooth wind power plant is poor and the power fluctuation smoothing capability of the wind power plant is limited by introducing a virtual synchronous generator in the prior art, and the problem that the virtual synchronous generator runs unstably.
In order to solve the technical problem, the invention provides a wind power plant power control method based on an energy storage inverter, which comprises the following steps:
1) acquiring original active power output by a wind power plant and grid-connected voltage of a grid-connected point of the wind power plant, outputting expected grid-connected power of the wind power plant by the original active power output by the wind power plant through a low-pass filter, and subtracting the expected grid-connected power of the wind power plant and the original active power output by the wind power plant to obtain the expected output active power of the energy storage inverter; according to an instantaneous reactive power theory, calculating to obtain power smoothing instruction current under a two-phase static coordinate system by utilizing expected output active power of an energy storage inverter and grid-connected voltage of a grid-connected point of a wind power plant under the two-phase static coordinate system, and obtaining power smoothing instruction current under a three-phase static coordinate system through conversion from two phases to three-phase static coordinates;
2) calculating the stator current of the current control type virtual synchronous generator by utilizing a mathematical model of the current control type virtual synchronous generator;
3) and adding and summing the power smoothing instruction current and the stator current to obtain a target instruction current, and controlling the current output by the energy storage inverter to be the target instruction current.
The wind power plant power control method of the invention adopts the instantaneous reactive power theory to calculate the power smoothing instruction current, utilizes the power smoothing instruction current to smooth the power fluctuation of the wind power plant, meanwhile, a mathematical model of a current control type virtual synchronous generator (hereinafter referred to as a virtual synchronous generator) is established, the stator current of the virtual synchronous generator is calculated, and the power smooth instruction current and the stator current of the virtual synchronous generator are added and synthesized, so that the energy storage inverter has various beneficial characteristics (such as inertia, damping, voltage regulation and primary frequency modulation) of the virtual synchronous generator while smoothing power fluctuation, the wind power plant power fluctuation smoothing function generated by the power smoothing instruction current does not influence the operation of the virtual synchronous generator, so that the problem of serious mechanical power fluctuation of the virtual synchronous generator is avoided, and the operation state of the virtual synchronous generator is stable.
Meanwhile, the instantaneous reactive power theory is adopted to directly calculate the power smoothing instruction current, the power smoothing instruction current is calculated without depending on a virtual synchronous generator algorithm, and the power smoothing instruction current has no relation with the rotational inertia of the virtual generator, so that the influence of the rotational inertia of the virtual synchronous generator on the power smoothing function is avoided. Therefore, the wind power plant power control method of the invention not only ensures the stable operation of the virtual synchronous generator, but also has the power smoothing function without being restricted by the rotational inertia of the virtual synchronous generator.
To achieve the calculation of the power smoothing command current, a calculation formula for providing the power smoothing command current is as follows:
in the formula iα_aps、iβ_apsα phase and β phase power smoothing command currents u under a two-phase static coordinate systema、uβGrid-connected voltages of grid-connected points of α -phase wind power plants and β -phase wind power plants under a two-phase static coordinate system are provided, and p is expected output active power of the energy storage inverter.
In order to provide a concrete implementation method of the stator current of the current control type virtual synchronous generator, the mathematical model comprises a rotor motion equation, a stator electrical equation, an active adjusting module for generating mechanical power and a reactive adjusting module for generating exciting electromotive force, wherein the mechanical power generated by the active adjusting module is substituted into the rotor motion equation to obtain the electric angle of the exciting electromotive force of the mathematical model; and substituting the excitation electromotive force and the electrical angle thereof into a stator electrical equation, and calculating to obtain the stator current by combining the known stator terminal voltage.
In order to realize the generation of the mechanical power of the mathematical model by using the active power regulation module, the specific steps are as follows: and (3) making a difference between the actual electrical angular velocity and the rated electrical angular velocity of the current control type virtual synchronous generator, multiplying the electrical angular velocity difference obtained by making the difference by an active-frequency droop coefficient, and summing the electrical angular velocity difference and an active power given value to obtain the mechanical power. Compared with the power frequency controller in the prior art, the active adjusting module does not have the output power of the wind power plant, namely the active adjusting module does not have the fluctuation power component of the wind power plant, the output mechanical power is relatively stable, and the stable operation of the virtual synchronous generator is ensured. In addition, in the prior art, the grid-connected power instruction of the wind power plant, namely the rated active power of the virtual synchronous generator, is a value of the MPPT output active power of the wind power plant after low-pass filtering, and the value cannot be set manually, so that the virtual synchronous generator does not have the secondary frequency modulation capability.
In order to realize the tracking control of the target command current, the method comprises the following steps:
taking the target instruction current as a current reference value to make a difference with the grid side inductive current of the energy storage inverter, outputting a modulation voltage by a quasi-PR controller according to a difference value obtained by making the difference, overlapping the modulation voltage with a grid voltage feedforward value to obtain the output voltage of the energy storage inverter after overlapping, and realizing the tracking control of the target instruction current at the grid side inductive current of the energy storage inverter;
the calculation formula of the output voltage of the energy storage inverter is as follows:
in the formula of Uinv(s) is the output voltage of the energy storage inverter, UPR(s) is the modulation voltage output by the quasi-PR controller, Uαβ(s) is the grid voltage, GLCL1(s) is the transfer function of the output voltage of the energy storage inverter to the network side inductor current, GLCL2(s) is the transfer function of the grid voltage to the grid side inductor current,
and the value is a power grid voltage feedforward value.
According to the invention, the interference of the power grid voltage on the output current of the energy storage inverter is eliminated by introducing the power grid voltage feedforward value, so that the output current of the energy storage inverter is only related to the modulation voltage output by the quasi-PR controller.
The transfer function of the quasi-PR controller is as follows:
in the formula, GPR(s) is the transfer function of the quasi-PR controller, kPIs a proportionality coefficient, kRIs the resonance coefficient, omega0Is a resonance frequency equal to the rotor angular frequency, ω, of said current-controlled virtual synchronous generatorcIs the resonance part bandwidth.
In order to solve the technical problem, the invention further provides a wind farm power control system based on an energy storage inverter, which comprises an energy storage battery, an inverter and a filter which are sequentially connected, wherein the filter is used for connecting a PCC (point of charge) between a wind farm and a power grid, the wind farm power control system further comprises a control module and a PWM (pulse width modulation) module, the control module is connected with the PWM module, the PWM module is connected with a control end of the inverter, and the control module is used for executing instructions to realize the following steps:
1) acquiring original active power output by a wind power plant and grid-connected voltage of a grid-connected point of the wind power plant, outputting expected grid-connected power of the wind power plant by the original active power output by the wind power plant through a low-pass filter, and subtracting the expected grid-connected power of the wind power plant and the original active power output by the wind power plant to obtain the expected output active power of the energy storage inverter; according to an instantaneous reactive power theory, calculating to obtain power smoothing instruction current under a two-phase static coordinate system by utilizing expected output active power of an energy storage inverter and grid-connected voltage of a grid-connected point of a wind power plant under the two-phase static coordinate system, and obtaining power smoothing instruction current under a three-phase static coordinate system through conversion from two phases to three-phase static coordinates;
2) calculating the stator current of the current control type virtual synchronous generator by utilizing a mathematical model of the current control type virtual synchronous generator;
3) and adding and summing the power smoothing instruction current and the stator current to obtain a target instruction current, and controlling the current output by the energy storage inverter to be the target instruction current.
The wind power plant power control system adopts an instantaneous reactive power theory to calculate power smoothing instruction current, utilizes the power smoothing instruction current to smooth power fluctuation of a wind power plant, simultaneously establishes a mathematical model of a current control type virtual synchronous generator, calculates stator current of the virtual synchronous generator, and adds and synthesizes the power smoothing instruction current and the stator current of the virtual synchronous generator, so that an energy storage inverter has various beneficial characteristics (such as inertia, damping, voltage regulation and primary frequency modulation) of the virtual synchronous generator while smoothing the power fluctuation, and the wind power plant power fluctuation smoothing function generated by the power smoothing instruction current does not influence the operation of the virtual synchronous generator, thereby avoiding the problem of serious mechanical power fluctuation of the virtual synchronous generator and stabilizing the operation state of the virtual synchronous generator.
Meanwhile, the invention adopts the instantaneous reactive power theory to directly calculate the power smoothing instruction current, and does not depend on the virtual synchronous generator algorithm to calculate the power smoothing instruction current, thereby avoiding the influence of the rotational inertia of the virtual synchronous generator on the power smoothing function. In the above patent, "a method for controlling an energy storage wind farm with grid-connected characteristics" utilizes the power generated by the virtual synchronous generator algorithm to offset the fluctuation component in the wind power to achieve the effect of power smoothing, and is influenced by the rotor inertia of the virtual synchronous generator, because the active power generated by the virtual generator has a close relationship with the power angle, and the change of the power angle requires the acceleration or deceleration of the rotor, the acceleration and deceleration process is relatively slow due to the rotor inertia, and the larger the rotor inertia is, the larger the influence on the acceleration and deceleration process is. Therefore, the wind power plant power control system not only realizes the rapid and smooth power fluctuation of the wind power plant, but also ensures the stable operation of the virtual synchronous generator.
To achieve the calculation of the power smoothing command current, a calculation formula for providing the power smoothing command current is as follows:
in the formula ia_aps、iβ_apsAre respectively provided withSmoothing command currents u for α and β phases of power in a two-phase stationary coordinate systemα、uβGrid-connected voltages of grid-connected points of α -phase wind power plants and β -phase wind power plants under a two-phase static coordinate system are provided, and p is expected output active power of the energy storage inverter.
In order to provide a specific implementation mode of the stator current of the current control type virtual synchronous generator, the mathematical model comprises a rotor motion equation, a stator electrical equation, an active adjusting module for generating mechanical power and a reactive adjusting module for generating exciting electromotive force, wherein the mechanical power generated by the active adjusting module is substituted into the rotor motion equation to obtain the electric angle of the exciting electromotive force of the mathematical model; and substituting the excitation electromotive force and the electrical angle thereof into a stator electrical equation, and calculating to obtain the stator current by combining the known stator terminal voltage.
In order to provide a concrete implementation of the mechanical power of the active power regulating module for generating the mathematical model, the steps are as follows: and (3) making a difference between the actual electrical angular velocity and the rated electrical angular velocity of the current control type virtual synchronous generator, multiplying the electrical angular velocity difference obtained by making the difference by an active-frequency droop coefficient, and summing the electrical angular velocity difference and an active power given value to obtain the mechanical power. Compared with the power frequency controller in the prior art, the active adjusting module does not have the output power of the wind power plant, namely, the active adjusting module does not have the fluctuation power component of the wind power plant, the output mechanical power is relatively stable, and the stable operation of the virtual synchronous generator is further ensured. In addition, in the prior art, the grid-connected power instruction of the wind power plant is also the rated active power of the virtual synchronous generator and is a value of the MPPT output active power of the wind power plant after low-pass filtering, and the value cannot be set manually, so that the virtual synchronous generator does not have the secondary frequency modulation capability.
In order to realize the tracking control of the target command current, the method comprises the following steps:
taking the target instruction current as a current reference value to make a difference with the grid side inductive current of the energy storage inverter, outputting a modulation voltage by a quasi-PR controller according to a difference value obtained by making the difference, overlapping the modulation voltage with a grid voltage feedforward value to obtain the output voltage of the energy storage inverter after overlapping, and realizing the tracking control of the target instruction current at the grid side inductive current of the energy storage inverter;
the calculation formula of the output voltage of the energy storage inverter is as follows:
in the formula of Uinv(s) is the output voltage of the energy storage inverter, UPR(s) is the modulation voltage output by the quasi-PR controller, Uαβ(s) is the grid voltage, GLCL1(s) is the transfer function of the output voltage of the energy storage inverter to the network side inductor current, GLCL2(s) is the transfer function of the grid voltage to the grid side inductor current,
for the grid voltage feedforward value, the variables and the transfer function in the above formula are in the form of laplace transform.
According to the invention, the interference of the power grid voltage on the output current of the energy storage inverter is eliminated by introducing the power grid voltage feedforward value, so that the output current of the energy storage inverter is only related to the modulation voltage output by the quasi-PR controller.
The transfer function of the quasi-PR controller is as follows:
in the formula, GPR(s) is the transfer function of the quasi-PR controller, kPIs a proportionality coefficient, kRIs the resonance coefficient, omega0Is a resonance frequency equal to the rotor angular frequency, ω, of said current-controlled virtual synchronous generatorcIs the resonance part bandwidth.
Drawings
FIG. 1 is a schematic diagram of a prior art power fluctuation suppression function;
FIG. 2 is an equivalent circuit diagram of a prior art virtual synchronous generator operating grid-tied;
FIG. 3 is a schematic diagram of a prior art power frequency controller;
FIG. 4 is a schematic diagram of an energy storage inverter based wind farm power control system of the present invention;
FIG. 5 is a schematic diagram of the power fluctuation suppression function of the present invention;
FIG. 6 is a schematic diagram of the present invention for deriving a power smoothing command current;
FIG. 7 is a schematic diagram of a control algorithm for a current-controlled virtual synchronous generator of the prior art;
FIG. 8 is a schematic diagram of the present invention to obtain a target command current;
fig. 9 is a schematic diagram of a current tracking control method of the inverter of the present invention.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
The energy storage inverter-based wind farm power control system shown in fig. 4 comprises an energy storage inverter, wherein the energy storage inverter comprises an energy storage battery, an inverter and an LCL filter which are connected in sequence, the LCL filter is used for connecting a PCC (common connection point) between a wind farm and a power grid, the wind farm power control system further comprises a control module and a PWM module, the control module is connected with the PWM module, the PWM module is connected with a control end of the inverter, the control module is used for controlling the PWM module to output a PWM wave, the PWM wave acts on the inverter to enable the inverter to output a corresponding voltage, and the voltage acts on the LCL filter (hereinafter referred to as the filter) to generate a desired target command current on the filter. The control module is used for executing instructions to control the inverter to output expected target instruction current through the filter, and realizes the wind power plant power control based on the energy storage inverter, and the specific implementation steps are as follows:
obtaining original active power P output by wind power plantmgGrid-connected voltage u of grid-connected point of wind power planta、ub、ucCalculating the expectation of the wind farmNetwork power PmlWherein the desired grid-connected power P of the wind farmmlObtained from the power smoothing principle as shown in fig. 5, the calculation is as follows:
Pml＝Pmg×1/(1+Ts)
where T is the time constant of the power low pass filter.
Combining the expected grid-connected power P of the wind power plantmlOriginal active power P output by wind power plantmgObtaining the expected output active power P of the energy storage inverter by differencebh. The principle of smoothing the power fluctuation of the wind power plant by using the energy storage inverter is as follows:
as shown in FIG. 4, PmgThe original active power generated by the wind power plant is greatly influenced by the wind speed, the fluctuating frequency component is also complex, and P issFor grid-connected power, for PsThe stability is small, the high-frequency fluctuation is small, and an energy storage inverter is added for the purpose, so that the actual active power emitted by the energy storage inverter is PbAccording to conservation of energy, there is Pmg+Pb＝PsTo stabilize PmgMedium high frequency fluctuation to make the energy storage inverter send out actual active power PbAnd PmgMedium high frequency ripple power is opposite in magnitude, so that Pmg+PbThe high frequency ripple power after the addition is cancelled out. To find PmgMedium high frequency fluctuating power, the invention will PmgFeeding into a first-order low-pass filter, the output of which is denoted as Pml，PmlIs PmgThe invention aims to reduce the grid-connected power P of a grid-connected point of a wind power plant, wherein the low-frequency component and the high-frequency component in the wind power plant are filtered by a low-pass filter, so that the fluctuation degree is greatly reducedsAnd PmlIn agreement, therefore PmlCalled desired grid-connected power, for Ps＝PmlTarget of (1), let Pmg-PmlNamely to obtain PmgMiddle high frequency component Pmh(i.e. P)mh＝Pmg-Pml) High frequency component PmhIs the component to be filtered, if the energy storage inverter is controlled to send out the actual active power Pb＝-PmhLet the inverter immediatelyDelivered power and PmgMedium and high frequency components are cancelled out, and grid-connected power P is obtaineds＝Pmg+Pb＝Pmg+Pml-Pmg＝PmlI.e. grid-connected power and PmgThe low frequency components in the medium are consistent, and the high frequency components are filtered out. It should be noted that, due to errors and delays in the control, the actual active power P emitted by the inverter isbNot necessarily exactly equal to Pml-PmgThus P ismlAnd PsNot exactly equal (but very close), so P will bemlReferred to as desired grid-connected power, PsFor actual grid-connected active power, P is addedbh＝-Pmh＝Pml-PmgDesired output active power, P, called storage inverterbReferred to as the actual active power drawn by the tank inverter.
According to the instantaneous reactive power theory, the grid-connected voltage u of the grid-connected point of the wind power planta、ub、ucGrid-connected voltage u converted to two-phase stationary coordinate systemα、uβUnder a two-phase static coordinate system, the instantaneous active power and the instantaneous reactive power are respectively as follows:
p＝uαiα_aps+uβiβ_aps
q＝uβiα_aps-uαiβ_aps
wherein p is instantaneous active power, q is instantaneous reactive power, uα、uβGrid-connected voltage i of α -phase wind power plant and β -phase wind power plant under two-phase static coordinate systemα_aps、iβ_apsThe command currents for α phases and β phases in the two-phase stationary coordinate system are smoothed.
Since the smooth power fluctuation is directed to the active power, q is equal to 0, and the expected output active power P of the energy storage inverter is utilized in the two-phase static coordinate systembhAnd grid-connected voltage u under two-phase static coordinate systemα、uβCalculating to obtain power smoothing command current iα_aps、iβ_apsThe calculation formula is as follows:
then, the power is smoothed to the command current iα_aps、iβ_apsConverting the three-phase static coordinate system to obtain a power smoothing instruction current i in the three-phase static coordinate systemabc_apsAs shown in fig. 6.
The invention can avoid coordinate rotation transformation by calculating the power smoothing command current under the two-phase static coordinate system, thereby omitting a phase locking link and having simple calculation method.
The control algorithm module (i.e. mathematical model) of the current control type virtual synchronous generator (hereinafter referred to as virtual synchronous generator) is shown in fig. 7, and includes four modules, and the module ① corresponds to the rotor motion equation of the virtual synchronous generator, PmAnd PeMechanical power and electromagnetic power, respectively, and the input term is (P)m-Pe) D is a constant damping coefficient, △ omega is an electrical angular velocity difference, △ omega is omega-omegan，ωnAnd ω is the rated electrical angular velocity and the actual electrical angular velocity, respectively, J is the moment of inertia of the synchronous generator, and θ is the electrical angle.
The step of generating the mechanical power of the mathematical model by the active power regulation module comprises:
actual and rated electrical angular velocities ω to the virtual synchronous generatornMaking a difference, and making the electrical angular velocity difference △ omega obtained by making the difference and an active-frequency droop coefficient DpMultiplying, and then adding the given value P of active powersetSumming to obtain mechanical power Pm. P is abovesetThe method can be set according to the residual capacity of the energy storage battery and the requirement of secondary frequency modulation of the power grid, and is a relatively stable value.
Mechanical power P generated by active power regulating modulemSubstituting the rotor motion equation to obtain the exciting electromotive force E of the mathematical modelabcElectrical angle theta of (1), exciting electromotive force EabcSubstituting the electrical angle theta into the electrical equation of the stator, and combining the known stator terminal voltage uabcCalculating to obtain stator current iabc_vsg. Smoothing command current i for powerabc_apsAnd stator current iabc_vsgAdding and summing to obtain target command current iabc_objI.e. controlling the current output by the energy storage inverter through the filter as the target command current iabc_objAs shown in fig. 8.
If the inverter can send out the target command current, the inverter realizes the power fluctuation smoothing function and has the synchronous generator characteristics, namely the inertia and damping characteristics, frequency modulation/voltage regulation characteristics and the like similar to the synchronous generator, and therefore the following inverter sampling current tracking control method is provided for the target command current iabc_objPerforming tracking control, comprising the steps of:
as shown in fig. 9, the system includes a control link, a controlled object and grid voltage interference, where the controlled object is an LCL filter and its corresponding transfer function is GLCL1(s) the goal is to make the current through the inductor on the net side of the LCL filter equal to the target command current, since the net side inductor current through the LCL filter is the current from the inverter after filtering out unwanted higher harmonics near the PWM carrier. However, the LCL filter network side is electrically connectedThe current of the inductor is not only related to the output voltage of the inverter, but also to the network voltage UαβIn this regard, the current of the inductor on the network side of the LCL filter is represented as follows:
Iαβ(s)＝Uinv(s)GLCL1(s)+Uαβ(s)GLCL2(s)
wherein, Iαβ(s) is the current of the inductor on the network side of the LCL filter, Uinv(s) is the output voltage of the inverter, GLCL1(s) is the transfer function of the output voltage of the energy storage inverter to the network side inductor current, Uαβ(s) is the grid voltage, GLCL2(s) is the transfer function of the grid voltage to the grid side inductor current.
In order to eliminate the influence of the power grid voltage, a power grid voltage feedforward value is introduced, and a modulation voltage U is output by a quasi PR controllerPR(s) superimposing on top of such an item:
namely, it is
Wherein the content of the first and second substances,
for grid voltage feed-forward values, Gfd(s) is the feedback loop transfer function, UPR(s) is the modulation voltage output by the quasi-PR controller, and the network side inductive current of the energy storage inverter is as follows:
Iαβ(s)＝Uinv(s)GLCL1(s)+Uαβ(s)GLCL2(s)＝UPR(s)GLCL1(s)
in this way, the disturbance of the grid voltage to the LCL filter output current (i.e., the current of its grid side inductor) can be cancelled out, and the output current is only related to the modulation voltage output by the quasi-PR controller.
Therefore, the tracking control process in fig. 9 is as follows:
target command current iabc_objPerforming Clarke transformation (under three-phase static coordinate system) to convert to target command current i under two-phase static coordinate systemαβ_objI.e. iαβ_obj＝Tabc/αβiabc_obj，Tabc/αβTo transform the matrix, iαβ_objNetwork side inductive current i as current reference value and energy storage inverterαβMaking a difference, and outputting a modulation voltage by a quasi-PR controller according to the difference value obtained by making the difference, wherein the modulation voltage is umod＝[umodα，umodβ]TThe modulation voltage and the grid voltage feedforward value are superposed, and then the superposed values are used for generating PWM waves through a PWM module, the PWM waves act on the inverter to obtain the output voltage of the inverter, the output voltage acts on the LCL filter shown in the figure 4, and the desired target command current is generated on the filter.
The transfer function of the quasi-PR controller is as follows:
in the formula, GPR(s) is the transfer function of the quasi-PR controller, kPIs a proportionality coefficient, kRIs the resonance coefficient, omega0Is the resonant frequency, omega0Adjusted in real time according to the rotor angular frequency of the virtual synchronous generator, i.e. ω0ω (rotor angular frequency in the rotor motion equation of block ① in fig. 7) in order to enhance the ability of the quasi-PR controller to adapt to frequency fluctuations, ωcFor resonant part of the bandwidth, ωc＝2πrad/s。
In conclusion, the calculation of the power smoothing instruction current does not depend on the mathematical model and the control algorithm of the virtual synchronous generator, but is directly calculated according to the power smoothing principle and the instantaneous reactive power theory, the fluctuation power does not act on the control algorithm of the virtual generator, and the influence of the power fluctuation on the virtual synchronous generator is avoided in principle.
In addition, the invention adopts the control algorithm of the current control type virtual synchronous generator to calculate the stator current of the virtual synchronous generator, adds the power smooth instruction current required by smooth power fluctuation and the stator current of the virtual synchronous generator to obtain the target instruction current, adopts the quasi-PR controller to carry out tracking control on the target instruction current, and leads the network side inductive current output by the filter of the inverter to be consistent with the target instruction current, thus, the inverter not only can play the role of smooth power fluctuation, but also has the characteristic of the virtual synchronous generator; meanwhile, the smooth function of power fluctuation does not influence the operation of the virtual synchronous generator, and the virtual synchronous generator stably operates no matter how the power fluctuates.
In addition, the invention adopts the instantaneous reactive power theory to directly calculate the power smoothing instruction current, and does not depend on the virtual synchronous generator algorithm to calculate the power smoothing instruction current, thereby avoiding the influence of the rotational inertia of the virtual synchronous generator on the power smoothing function. However, in the patent of "a method for controlling an energy storage wind farm with grid-connected characteristics" mentioned in the background art, the fluctuating power generated by the virtual synchronous generator algorithm is used to offset the fluctuating component in the wind power to achieve the effect of power smoothing, and the effect is influenced by the inertia of the rotor of the virtual synchronous generator. Therefore, the wind power plant power control method of the invention not only ensures the stable operation of the virtual synchronous generator, but also has the power smoothing function without being restricted by the rotational inertia of the virtual synchronous generator.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (5)
1. A wind power plant power control method based on an energy storage inverter is characterized by comprising the following steps:
1) acquiring original active power output by a wind power plant and grid-connected voltage of a grid-connected point of the wind power plant, outputting expected grid-connected power of the wind power plant by the original active power output by the wind power plant through a low-pass filter, and subtracting the expected grid-connected power of the wind power plant and the original active power output by the wind power plant to obtain the expected output active power of the energy storage inverter; according to an instantaneous reactive power theory, calculating to obtain power smoothing instruction current under a two-phase static coordinate system by utilizing expected output active power of an energy storage inverter and grid-connected voltage of a grid-connected point of a wind power plant under the two-phase static coordinate system, and obtaining power smoothing instruction current under a three-phase static coordinate system through conversion from two phases to three-phase static coordinates;
2) calculating the stator current of the current control type virtual synchronous generator by utilizing a mathematical model of the current control type virtual synchronous generator;
3) adding and summing the power smoothing instruction current and the stator current to obtain a target instruction current, and controlling the current output by the energy storage inverter to be the target instruction current;
the calculation formula of the power smoothing command current in the two-phase static coordinate system is as follows:
in the formula iα_aps、iβ_apsα phase and β phase power smoothing command currents u under a two-phase static coordinate systemα、uβGrid-connected voltages of grid-connected points of α -phase wind power plants and β -phase wind power plants under a two-phase static coordinate system respectively, wherein p is expected output active power of the energy storage inverter;
the mathematical model comprises a rotor motion equation, a stator electrical equation, an active regulation module for generating mechanical power and a reactive regulation module for generating exciting electromotive force, wherein the mechanical power generated by the active regulation module is substituted into the rotor motion equation to obtain the electric angle of the exciting electromotive force of the mathematical model; and substituting the excitation electromotive force and the electrical angle thereof into a stator electrical equation, and calculating to obtain the stator current by combining the known stator terminal voltage.
2. The energy storage inverter-based wind farm power control method according to claim 1, wherein the step of the active regulation module generating the mechanical power of the mathematical model comprises:
and (3) making a difference between the actual electrical angular velocity and the rated electrical angular velocity of the current control type virtual synchronous generator, multiplying the electrical angular velocity difference obtained by making the difference by an active-frequency droop coefficient, and summing the electrical angular velocity difference and an active power given value to obtain the mechanical power.
3. The energy storage inverter-based wind farm power control method according to claim 1, wherein the target command current is subjected to tracking control according to the following steps:
taking the target instruction current as a current reference value to make a difference with the grid side inductive current of the energy storage inverter, outputting a modulation voltage by a quasi-PR controller according to a difference value obtained by making the difference, overlapping the modulation voltage with a grid voltage feedforward value to obtain the output voltage of the energy storage inverter after overlapping, and realizing the tracking control of the target instruction current at the grid side inductive current of the energy storage inverter;
the calculation formula of the output voltage of the energy storage inverter is as follows:
in the formula of Uinv(s) is the output voltage of the energy storage inverter, UPR(s) is the modulation voltage output by the quasi-PR controller, Uαβ(s) is the grid voltage, GLCL1(s) is the transfer function of the output voltage of the energy storage inverter to the network side inductor current, GLCL2(s) is the transfer function of the grid voltage to the grid side inductor current,
and the value is a power grid voltage feedforward value.
4. The energy storage inverter-based wind farm power control method according to claim 3, wherein the transfer function of the quasi-PR controller is as follows:
in the formula，GPR(s) is the transfer function of the quasi-PR controller, kPIs a proportionality coefficient, kRIs the resonance coefficient, omega0Is a resonance frequency equal to the rotor angular frequency, ω, of said current-controlled virtual synchronous generatorcIs the resonance part bandwidth.
5. A wind farm power control system based on an energy storage inverter comprises an energy storage battery, an inverter and a filter which are sequentially connected, wherein the filter is used for being connected with a PCC between a wind farm and a power grid, the wind farm power control system further comprises a control module and a PWM module, the control module is connected with the PWM module, the PWM module is connected with a control end of the inverter, and the wind farm power control system based on the energy storage inverter is characterized in that the control module is used for realizing the wind farm power control method based on the energy storage inverter according to any one of claims 1-4.
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