CN117977706A - Novel double closed-loop control method for wind power grid-connected inverter - Google Patents
Novel double closed-loop control method for wind power grid-connected 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
- 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
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
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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
- H02J2203/00—Indexing scheme relating to details of 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
- 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
- H02J2300/28—The renewable source being wind energy
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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
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
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Abstract
The invention discloses a novel double closed-loop control method of a wind power grid-connected inverter, which comprises the steps of firstly establishing a mathematical model of a wind power grid-connected inverter system; then, based on a mathematical model of the wind power grid-connected inverter system, a novel double closed loop structure controlled by LADRC and quasi PR is constructed, and finally, the control of DC bus voltage and the suppression of power grid harmonic waves are realized; the novel double-closed-loop structure takes a second-order LADRC voltage ring as an outer ring and takes a quasi PR control current ring as an inner ring; the novel double closed-loop structure does not depend on an accurate mathematical model of a controlled system, is simple in design and convenient to realize, and the voltage loop improves the disturbance resistance of the system by using the LADRC algorithm, so that the voltage of a direct current bus is more stable; the current loop solves the coupling problem between dq axis currents by using a quasi PR control algorithm, saves one-time coordinate transformation, can effectively inhibit grid-connected current harmonic waves, and improves the quality of grid-connected current.
Description
Technical Field
The invention relates to the field of wind power generation control, in particular to a novel double closed-loop control method of a wind power grid-connected inverter.
Background
The wind power grid-connected inverter is used as a core element of the direct-drive permanent magnet wind power generation system and is a key interface for converting direct current into alternating current; however, due to uncertainty and intermittence of wind, nonlinearity of the converter and strong coupling, the wind power grid-connected inverter is disturbed by an inner part and an outer part, namely: disturbance caused by change of internal parameters of the converter and disturbance caused by change of external conditions. The disturbances have great influence on the direct current bus voltage, the quality of electric energy output and the switching of the power grid under multiple working conditions; in order to stabilize direct-current voltage and improve grid-connected power quality, improving a control strategy of a wind power grid-connected inverter is the focus of current research.
At present, a voltage-current double-closed-loop PI control structure is mainly adopted for controlling the wind power grid-connected inverter. The voltage outer ring controls the DC bus voltage to be maintained at a given value, and the output value is used as the input of the current inner ring. And the current inner loop adjusts a reference value for generating reactive power according to the reactive power requirement of the wind turbine generator, so that the control effect of the voltage outer loop is improved. Therefore, the current loop plays an important role in the control of the wind power grid-connected inverter. However, coupling problems exist in the current of the dq axis of the current inner loop, and the control effect of the wind power grid-connected inverter can be affected. In addition, the traditional double-closed-loop PI control strategy is realized by compensating errors, but compared with external interference, the passive control method has hysteresis, has weak inhibition capability on variation and unknown disturbance, and is difficult to solve the contradiction between response rapidity and overshoot. In addition, the traditional PI control strategy needs to perform a complex decoupling process, circuit device parameters have a larger influence on the design of a control system, and when the PI control parameters are determined, the characteristics of a transfer function of the system and the sampling period of PWM signals need to be considered, so that the calculation complexity is possibly increased, the double-closed-loop PI control strategy is sensitive to the change of the control parameters and has poor robustness, and therefore, a novel double-closed-loop control method of the wind power grid-connected inverter needs to be designed to solve the problems.
Disclosure of Invention
The invention aims to solve the technical problem of providing a novel double closed loop control method for a wind power grid-connected inverter, which improves the anti-interference performance of direct-current side voltage through the application of LADRC technology on a voltage outer ring, and greatly improves the anti-interference performance of direct-current bus voltage under normal working conditions and grid fault working conditions; the current inner loop effectively reduces the harmonic content of the output current at the network side while improving the response rate of the system by using the quasi PR control technology, and saves primary coordinate transformation.
In order to achieve the technical effects, the technical scheme adopted by the invention is as follows:
A novel double closed-loop control method of a wind power grid-connected inverter comprises the following steps:
S1, establishing a mathematical model of a wind power grid-connected inverter system;
S2, based on a mathematical model of the wind power grid-connected inverter system, a novel double closed-loop control structure is constructed, and direct current bus voltage control and grid-connected current harmonic suppression are achieved.
Preferably, in step S1, the voltage relationship of the wind power grid-connected inverter in the dq rotation coordinate system is:
The current relationship is:
Where U gd and U gq are components of the output voltage of the grid-side inverter on the d and q axes, e gd and e gq are components of the output current of the three-phase grid voltage on the d and q axes, i gd and i gq are components of the output current of the grid-side inverter on the d and q axes, ω is the fundamental angular velocity of the grid voltage, S d and S q are components of the switching function on the d and q axes, L is an ac equivalent filter inductance, C is a dc side voltage stabilizing capacitor, and U dc is a dc side output voltage.
Preferably, in step S1, the wind power grid-connected inverter controls the active power to control the dc bus voltage, and controls the reactive power to achieve unit power factor grid-connection.
Preferably, in step S2, the novel dual closed loop control structure uses the second-order ladc voltage ring as an outer ring and the quasi-PR control current ring as an inner ring.
Preferably, the second-order LADRC includes a third-order linear extended state observer LES0, a linear state error feedback control law LSEF, and a dynamic compensation link.
Preferably, the third-order linear extended state observer LESO corresponding to the voltage loop of the second-order ladc is:
Wherein Z 1 is a tracking signal of a direct-current voltage reference value, Z 2 is a differential signal of Z 1, Z 3 is a tracking signal of total disturbance of a voltage ring, i d * is a d-axis reference current, U dc is an actual value of a direct-current bus voltage, ω 0 is an observer bandwidth of the voltage ring, and b 0 is a compensation factor of the voltage ring.
Preferably, the linear state error feedback control law LESF and the dynamic compensation link are:
Wherein u 0 is the output of the voltage loop controller, u is the input of the controlled object of the voltage loop, ω c is the controller bandwidth of the voltage loop, Is a reference value for the dc bus voltage.
Preferably, in step S2, the transfer function of the current inner loop PR controller is:
wherein K p is a proportional element coefficient, and influences the amplitude value outside the resonant frequency of the controller; k r is a resonance factor, and influences the gain of the full frequency range of the controller; omega c is cut-off frequency, and determines the bandwidth of control; the larger the omega c, the larger the controller bandwidth; ω 0 is the resonant frequency, ω 0 =100 pi rad/s.
The novel double closed-loop control method for the wind power grid-connected inverter has the following beneficial effects:
1, the designed novel double closed-loop control structure does not depend on a mathematical model of system accuracy, and is simple in design and easy to realize;
2, the voltage loop uses a second-order LADRC technology to treat internal and external disturbance of the inverter system as total disturbance, and estimates and compensates the total disturbance, so that the anti-disturbance performance of the system is improved, and the DC bus voltage can be quickly stabilized;
And 3, the current loop is designed by using quasi PR control, decoupling control is not needed for current components, primary coordinate transformation is saved, the response rate of the system is improved, and meanwhile, the harmonic content of the output current at the network side is effectively reduced.
Drawings
FIG. 1 is a schematic flow chart of the invention;
FIG. 2 is a circuit topology of a wind power grid-connected inverter of the present invention;
FIG. 3 is a second order LADRC structure according to the present invention;
FIG. 4 is a diagram of a voltage outer loop second order LADRC control architecture of the present invention;
FIG. 5 is a block diagram of a novel dual closed loop control architecture of the present invention;
FIG. 6 is a waveform comparison chart of DC bus voltage under two control strategies under normal working conditions of the invention;
FIG. 7 is a graph showing analysis of current harmonic content under two control strategies according to the present invention;
FIG. 8 is a waveform of DC bus voltage under two control strategies under disturbance conditions of the present invention.
Detailed Description
Embodiment one:
As shown in fig. 1, a novel double closed-loop control method for a wind power grid-connected inverter includes:
S1, establishing a mathematical model of a wind power grid-connected inverter system;
S2, based on a mathematical model of the wind power grid-connected inverter system, a novel double closed-loop control structure is constructed, and direct current bus voltage control and grid-connected current harmonic suppression are achieved.
Preferably, in step S1, the voltage relationship of the wind power grid-connected inverter in the dq rotation coordinate system is:
The current relationship is:
Where U gd and U gq are components of the output voltage of the grid-side inverter on the d and q axes, e gd and e gq are components of the output current of the three-phase grid voltage on the d and q axes, i gd and i gq are components of the output current of the grid-side inverter on the d and q axes, ω is the fundamental angular velocity of the grid voltage, S d and S q are components of the switching function on the d and q axes, L is an ac equivalent filter inductance, C is a dc side voltage stabilizing capacitor, and U dc is a dc side output voltage.
Preferably, in step S1, the wind power grid-connected inverter controls the active power to control the dc bus voltage, and controls the reactive power to achieve unit power factor grid-connection.
Preferably, in step S2, the novel dual closed loop control structure uses the second-order ladc voltage ring as an outer ring and the quasi-PR control current ring as an inner ring.
Preferably, the second-order LADRC includes a third-order linear extended state observer LES0, a linear state error feedback control law LSEF, and a dynamic compensation link.
Preferably, the third-order linear extended state observer LESO corresponding to the voltage loop of the second-order ladc is:
Wherein Z 1 is a tracking signal of a direct-current voltage reference value, Z 2 is a differential signal of Z 1, Z 3 is a tracking signal of total disturbance of a voltage ring, i d * is a d-axis reference current, U dc is an actual value of a direct-current bus voltage, ω 0 is an observer bandwidth of the voltage ring, and b 0 is a compensation factor of the voltage ring.
Preferably, the linear state error feedback control law LESF and the dynamic compensation link are:
Wherein u 0 is the output of the voltage loop controller, u is the input of the controlled object of the voltage loop, ω c is the controller bandwidth of the voltage loop, Is a reference value for the dc bus voltage.
Preferably, in step S2, the transfer function of the current inner loop PR controller is:
wherein K p is a proportional element coefficient, and influences the amplitude value outside the resonant frequency of the controller; k r is a resonance factor, and influences the gain of the full frequency range of the controller; omega c is cut-off frequency, and determines the bandwidth of control; the larger the omega c, the larger the controller bandwidth; ω 0 is the resonant frequency, ω 0 =100 pi rad/s.
Embodiment two:
in specific implementation, the novel double closed-loop control method for the wind power grid-connected inverter provided by the invention comprises the following steps:
Step S1, as shown in FIG. 2, a circuit topology structure of a wind power grid-connected inverter is shown, and six bridge arms of the inverter are composed of fully-controlled switching devices IGBT and freewheeling diodes; according to Kirchhoff Voltage Law (KVL) and Kirchhoff Current Law (KCL), simultaneously introducing a switching function, and obtaining a mathematical model of the wind power grid-connected inverter under a three-phase stationary coordinate system, wherein the mathematical model comprises the following steps:
Wherein e ga、egb、egc is three-phase grid voltage; i ga、igb、igc is three-phase grid-connected current; l is a network side filter inductor; r is the total impedance of the network side line; c is a direct-current side voltage stabilizing capacitor; i dc、Udc is direct current side output current and voltage respectively; u a、ub、uc is the inverter output phase voltage;
as can be seen from the above equation, the three-phase input current is controlled by the switching function, and by controlling the three-phase input current, the voltage of each phase output by the inverter can be adjusted, and the current is further changed, so that the purpose of transmitting electric energy from the inverter to the power grid is achieved. However, the mathematical model in the three-phase stationary coordinates is an alternating current, which would cause difficulty in designing the controller.
In order to simplify the design of the control system, a mathematical model in a three-phase static coordinate system is required to be converted into a model in a two-phase synchronous rotation coordinate system, and the time-varying alternating current quantity is required to be converted into direct current quantity; through the principle of equal power conversion, the voltage relation under the d-q two-phase rotation coordinate system is established as follows:
Wherein u gd、ugq is the component of the output voltage of the grid-side inverter on the d and q axes, e gd、egq is the component of the voltage of the three-phase grid on the d and q axes, i gd、igq is the component of the output current of the grid-side inverter on the d and q axes, and omega is the fundamental angular frequency of the grid voltage;
The current relationship is:
Where S d、Sq is the component of the switching function on the d, q axes.
Step S2, based on the mathematical model of the wind power grid-connected inverter system established in the step S1, a novel double closed-loop control structure of the wind power grid-connected inverter is established, so that disturbance rejection control of direct current bus voltage is realized, and the harmonic content of a grid side is reduced;
in a two-phase rotating coordinate system, the grid voltage is oriented on the d-axis, with u gd＝E;ugq =0; according to the instantaneous power theory, the obtained active power and reactive power of the input network side are as follows:
the instantaneous value of the input power of the direct current side of the wind power grid-connected inverter is as follows:
Pdc＝Udc*Idc；(5)
Assuming that the power loss of the power electronic device is ignored, according to the principle of conservation of energy, the power of the alternating current side and the direct current side of the system are equal, namely:
P＝Pdc；(6)
Udc*Idc＝ugdigd；(7)
As can be seen from equation (7), the inverter dc side voltage U dc is proportional to the inverter output d-axis current component i gd. Control over the dc bus voltage U dc can be achieved by controlling the inverter to output active power, i.e., i gd can be controlled;
step S201: construction of a second order LADRC:
as shown in fig. 3, the second-order ladc is composed of three parts of a third-order linear extended state observer LESO, a linear state error feedback control rate LSEF, and an interference compensation part, regardless of the tracking differentiator;
Assume a second order system:
Wherein, a1 and a0 are system parameter information; u and y are input and output of the controlled object; w is external disturbance; b is the input gain; b0, inputting an estimated value of the control gain; f is all uncertainty factors and internal and external unknown disturbance in the system, and the differential signal of the f is represented by h.
Taking state variables: x 1＝y,x2＝h,x3 = f, the expansion state space of the second order system (8) is described as:
the corresponding third-order LESO corresponding to equation (9) is:
Wherein: z 1、z2、z3 is the state variable of the LESO, and z 1、z2 is the observer gain factor to be configured for tracking the system disturbance f, β 1、β2、β3 at the system output x 1、x2,z3, respectively. By selecting the appropriate β 1、β2、β3, z 1、z2、z3 of the LESO can quickly track x 1、x2 and f of the system;
Taking the control quantity u of the system as follows:
u＝(-z3+u0)/b0；(11)
A linear state error feedback control Law (LSEF) is used for control signal generation, which consists of a PD controller. The control signals are as follows:
u0＝kp(u-z1)-kdz2；(12)
The gain coefficients of the observer and the controller can be obtained through pole allocation parameterization:
β1＝3ω0,β2＝3ω0 2,β3＝ω0 3；(13)
kp＝ωc 2,kd＝2ωc；(14)
Through the analysis, the second-order LADRC can be simplified into control of the bandwidth omega 0 of the observer and the bandwidth omega c of the controller, and a good control effect can be obtained by reasonably adjusting the two parameters.
Step S202: based on second-order LADRC structure, constructing second-order LADRC voltage outer ring
And (3) deriving and simplifying a direct-current voltage equation in the formula (3):
the state space expression corresponding to the voltage outer ring can be obtained according to the formula (9):
In the voltage loop compensation factor X 1u is the actual value of the dc bus voltage, and x 2u is the derivative of x 1u. u u represents a reference value of d-axis current, u u is taken as an input of a controlled object of the voltage ring, x 3u is a new state variable expanded by LESO, which is used for describing the total disturbance of the voltage ring and is marked as follows:
And/>
The third-order LESO corresponding to the voltage outer loop can be obtained according to the formula (10) as follows:
Wherein: z 1u、z2u、z3u is the state variable of the LESO, z 1u、z2u tracks the system output x 1u、x2u,z3u tracks the system disturbance f, I d * is a reference value of d-axis current, and ω 0u is an observer bandwidth of the voltage loop.
By selecting proper omega 0u, z 1u、z2u、z3u of the third-order LESO can quickly track the voltage reference value of the direct current busAnd the total disturbance f of the voltage loop.
LSEF and a dynamic compensation link are as follows:
Where u 0u is the output of the voltage loop controller and u u is the input of the voltage loop controlled object.
As shown in fig. 4, a voltage outer loop second order ladc control structure is obtained from the above analysis.
Step S203: the current inner loop is constructed based on quasi-PR control, and the transfer function of the quasi-PR controller is as follows:
Where K p is a proportionality element coefficient, K r is a resonance factor, ω c is a cutoff frequency, ω 0 is a resonance frequency, and ω 0 =100 pi rad/s.
The value of omega c,Kr,Kp is reasonably selected, so that the quasi PR controller can achieve both steady-state and anti-interference performance.
Transforming formula (1) into a two-phase stationary coordinate system to obtain:
Wherein e gα、egβ、ugα、ugβ、igα、igβ is the three-phase grid voltage, the inverter output phase voltage and the three-phase grid current under the two-phase stationary coordinate system respectively.
In formula (19), v* gα＝egα-u* gα,v* gβ＝egβ-u* gβ, is given by:
From the above equation, i gα and i gβ can be controlled by selecting v * gα and v * gβ, respectively.
Step S204: based on a voltage outer ring of a second-order LADRC and a quasi PR controlled current inner ring, a novel double closed-loop control structure is constructed, and control of direct-current bus voltage and harmonic suppression of network side current are realized:
As shown in fig. 5, the novel double closed-loop control structure of the wind power grid-connected inverter comprises:
(1) In the voltage outer ring, taking a reference value of direct current bus voltage as an input end of a second-order LADRC of the voltage ring, comparing the reference value with a bus voltage value estimated by a third-order LESO, and then obtaining a given value of d-axis current through LSEF and an interference compensation link; the output value of the voltage loop and the measured value of the direct current bus voltage are used as two inputs of LESO;
(2) In the current inner loop, d-axis reference current obtained by the voltage outer loop and given q-axis reference current are subjected to Park inverse transformation to obtain deviation signals of i * gα and i * gβ.i* gα,i* gβ which are compared with i gα,igβ, v * gα and v * gβ are respectively obtained through a quasi PR controller, u * gα and u * gβ can be obtained according to a formula (20), and finally control pulses of three pairs of full-control devices are obtained through an SVPWM algorithm.
In order to further verify the control effect of the invention, the control effect of the novel double-closed-loop structure is compared with that of the traditional double-closed-loop PI structure: firstly, constructing a simulation model of the wind power grid-connected inverter by utilizing MATLAB/Simulink, and comparing control effects under two control modes.
Fig. 6 shows waveforms of dc bus voltages under two control modes under normal conditions, and it can be seen that the time for the dc bus voltage waveform to reach steady state is shorter and overshoot is smaller by adopting the novel dual closed loop control strategy.
FIG. 7 is a comparison of harmonic content under normal conditions in two control modes, respectively, resulting in a smaller harmonic content when the novel dual closed loop control strategy is employed.
Fig. 8 is a comparison of dc bus voltages of two control modes under a disturbance condition, and when the power grid voltage is suddenly changed, the fluctuation range and the transition process of the dc bus voltage when the novel double-closed-loop control strategy is adopted are smaller than those of the double-closed-loop PI control strategy, which indicates that the disturbance rejection performance when the power grid is in fault is better when the novel double-closed-loop control structure is adopted.
The LADRC adopts a dynamic compensation link to treat uncertainty in the system and internal and external unknown disturbance as total disturbance, and compensates the system into an integral series system. Then, the controlled system is controlled using a widely applicable error feedback control law. The technology is obviously superior to the traditional PI controller in the aspects of decoupling performance, anti-interference performance and the like. There are a wide range of applications including motor speed regulation systems, photovoltaic systems and control of wind power systems.
The LADRC treats all uncertainty factors affecting the control of the system as a total disturbance, estimates and compensates for it, and can simplify the system to an integrator cascade to achieve the desired control performance. And the design and parameter setting are simple, the response speed is high, and the anti-interference capability is strong. Meanwhile, the quasi PR control can directly control the alternating current quantity, has larger gain in a small range at the fundamental frequency, can meet the fluctuation of the power grid frequency, and can effectively inhibit harmonic waves. Based on the method, the double closed-loop PI control strategy is improved based on the double closed-loop control strategy; the voltage outer loop provides reference current for the current inner loop through a second-order LADRC algorithm, and the current inner loop generates SVPWM modulation algorithm reference signals by adopting a quasi PR control algorithm; the control strategy of the scheme has simple structure, can improve the disturbance rejection performance of the system, reduce the harmonic wave of parallel current and avoid complex coordinate transformation.
Claims (8)
1. The novel double closed-loop control method for the wind power grid-connected inverter is characterized by comprising the following steps of:
S1, establishing a mathematical model of a wind power grid-connected inverter system;
S2, based on a mathematical model of the wind power grid-connected inverter system, a novel double closed-loop control structure is constructed, and direct current bus voltage control and grid-connected current harmonic suppression are achieved.
2. The novel double closed-loop control method of the wind power grid-connected inverter according to claim 1, wherein in step S1, the voltage relationship of the wind power grid-connected inverter under the dq rotation coordinate system is as follows:
The current relationship is:
Where U gd and U gq are components of the output voltage of the grid-side inverter on the d and q axes, e gd and e gq are components of the output current of the three-phase grid voltage on the d and q axes, i gd and i gq are components of the output current of the grid-side inverter on the d and q axes, ω is the fundamental angular velocity of the grid voltage, S d and S q are components of the switching function on the d and q axes, L is an ac equivalent filter inductance, C is a dc side voltage stabilizing capacitor, and U dc is a dc side output voltage.
3. The novel double closed-loop control method of the wind power grid-connected inverter according to claim 1 is characterized in that in step S1, the wind power grid-connected inverter controls the active power to control the direct current bus voltage, and controls the reactive power to realize unit power factor grid connection.
4. The novel double closed-loop control method of the wind power grid-connected inverter according to claim 1, wherein in the step S2, the novel double closed-loop control structure takes a second-order LADRC voltage ring as an outer ring and takes a quasi PR control current ring as an inner ring.
5. The novel double closed-loop control method of the wind power grid-connected inverter according to claim 1, wherein the second-order LADRC comprises a third-order linear extended state observer LES0, a linear state error feedback control law LSEF and a dynamic compensation link.
6. The novel double closed-loop control method of a wind power grid-connected inverter according to claim 1, wherein in step S2, a third-order linear extended state observer LESO corresponding to a voltage loop of the second-order ladc is:
Wherein Z 1 is a tracking signal of a direct-current voltage reference value, Z 2 is a differential signal of Z 1, Z 3 is a tracking signal of total disturbance of a voltage ring, i d * is a d-axis reference current, U dc is an actual value of a direct-current bus voltage, ω 0 is an observer bandwidth of the voltage ring, and b 0 is a compensation factor of the voltage ring.
7. The novel double closed-loop control method of the wind power grid-connected inverter according to claim 1, wherein the linear state error feedback control law LESF and the dynamic compensation link are as follows:
Wherein u 0 is the output of the voltage loop controller, u is the input of the controlled object of the voltage loop, ω c is the controller bandwidth of the voltage loop, Is a reference value for the dc bus voltage.
8. The novel double closed-loop control method of a wind power grid-connected inverter according to claim 1, wherein in step S2, a transfer function of the current inner loop quasi PR controller is:
Wherein K p is a proportional element coefficient, and influences the amplitude value outside the resonant frequency of the controller; k r is a resonance factor, and influences the gain of the full frequency range of the controller; omega c is cut-off frequency, and determines the bandwidth of control; the larger the omega c, the larger the controller bandwidth; ω 0 is the resonant frequency, ω 0 =100 pi rad/s.
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