CN110289618A - A kind of grid-connected power quality compensation control method of multifunction energy storage current transformer - Google Patents
A kind of grid-connected power quality compensation control method of multifunction energy storage current transformer 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
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- 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
- 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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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
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Abstract
The invention discloses a kind of grid-connected power quality compensation control methods of multifunction energy storage current transformer, the generating principle of electric current is compensated according to multiple target, using parallel resonance controller rapidly and accurately selective compensation harmonic, idle and out-of-balance current, the preliminary improvement to grid entry point power quality is realized；Simultaneously, it is contemplated that influence of the line impedance to stability of control system establishes PCS Robust Adaptive Control model under complex electric network environment, tracks desired value coefficient lambda according to set line impedanceexpReal-time change value coefficient λ is tracked with line impedancereal, and predictive control algorithm discretization adaptive model based control is utilized, to eliminate the control system Parameter Perturbation because of caused by line impedance, to enhance the adaptability and Ability of Resisting Disturbance of PCS.Frequency dividing control device, adaptive model based control and predictive control algorithm are combined together by method of the invention, can effectively improve the power quality under micro-grid connection operating status.
Description
Technical Field
The invention relates to grid-connected power quality compensation control, in particular to a grid-connected power quality compensation control method for a multifunctional energy storage converter.
Background
Renewable energy sources are used for replacing traditional fossil energy sources to generate electricity, which is a main development direction of energy utilization, and meanwhile, in the utilization of distributed renewable energy sources, a micro-grid technology plays an important role. Improving the power generation permeability of new energy and enabling the new energy to be safely and effectively connected into a power grid is a core target for forming and developing micro-grid technology. The micro-grid technology can not only realize the requirement of important load safe operation on the quality of electric energy, but also actively provide the support on power when necessary. Therefore, the micro-grid power quality control is one of the key technologies for ensuring the achievement of the above objects, and the related technologies are actively promoted so as to better serve the micro-grid and the power distribution network and promote the efficient integration of the system.
Compared with the traditional power generation power grid, the micro-grid is more beneficial to saving energy, but is more sensitive to randomness and intermittence of distributed power generation output such as wind injection, light injection and the like, so that the safety and the stability of the micro-grid are poor. The quality of the electric energy output by the energy storage converter is mainly influenced by a current control strategy, and according to the basic target of grid-connected current, on the premise of meeting the requirement that the output current can accurately track the reference input, the transient tracking time is reduced as much as possible, and the accurate and rapid control requirement is realized. Because the micro-grid has many limitations, for example, the electric quantity that can hold is few, inertia is not strong, and the application of control strategies such as droop control is added simultaneously, and load nonlinearity, unbalance sudden change and other conditions cause that the electric energy quality problems such as micro-grid current harmonic, three-phase voltage unbalance, voltage drop and frequency drift fluctuation are more outstanding than the big electric wire netting. The current control strategy cannot enable the converter to still effectively maintain grid-connected output and have good performance under the condition of reduced power quality.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a grid-connected power quality compensation control method for a multifunctional energy storage converter, which combines a frequency division controller, a self-adaptive control model and a prediction control algorithm to improve the power quality of a micro-grid in a grid-connected operation state.
The technical scheme is as follows: the invention provides a grid-connected power quality compensation control method for a multifunctional energy storage converter, which comprises the following steps:
(1) synthesizing the command current: detecting a current Δ I to be compensated in an electrical networkabchIs compared with a grid-connected current reference value delta IabcCompounding to obtain command currentNamely, it is wherein ΔIabchThe method comprises the following steps of (1) including reactive current, harmonic current and three-phase unbalanced current;
(2) generating a current tracking error: detecting compensated current I output by current transformerLabcComparing the command currentsAnd compensated current ILabcObtaining a current tracking error Ierr_abcI.e. by
(3) Introducing an adaptive controller to control the influence of the line impedance disturbance so as to ensure the stability of the current tracking error: based on controlled object Fp(x) And a low-pass filter W(s) for introducing a time-varying function L having an impedance elementg(s) constructing a standard self-adaptive model to obtain a stable suppressor K(s); will current tracking error Ierr_abcAnd adaptive controller output current Is_abcOf (2) synthesized current IabcThe adaptive control of the closed-loop system is realized as the input of an adaptive controller;
(4) will synthesize a current IabcThe frequency division controller is formed by connecting a plurality of specific subharmonic compensation control modules in parallel, and the compensation control modules corresponding to the specific subharmonic to be compensated are connected in parallel to obtain a frequency division control output UPVPI；
(5) Controlling the frequency division to output UPVPIThe PWM signal is generated through a pulse width modulation technology, and the energy storage converter is controlled to inject the compensated current I into the power gridLabc。
Further, the stable suppressor k(s) in step (3) is obtained by the following steps:
(31) according to the state equation of the energy storage converter, a time-varying function L with an impedance element is introducedg(s) as a transfer function in response to perturbation of line impedance:
according to the microgrid grid-connected equivalent circuit, the state equation of the energy storage converter can be expressed as:
wherein , C1＝[0 -1 0]，D1＝[0 1]，D2＝0；Rmg and LmgRespectively a PCS equivalent output resistor and an inductor; rline and LlineRespectively, line resistance and line inductance, Rpg and LpgRespectively a grid side resistance and a grid side inductance, Rpgl＝Rpg+Rline，Lpgl＝Lpg+Lline；
Let A01＝Rpgl/Lpgl，B01＝－1/LpglWhen the change of the grid side impedance is taken into account, then
in the formula,A0Representing a constant value of the corresponding impedance, B0Representing constant values of the corresponding inductive reactance, perturbation portions Δ A and Δ B, which can be expressed asWherein the perturbation parameterPredicted values for Δ A and Δ B; l isg(s) is an unknown time-varying function having a Lebesque measurable element, here as a transfer function responsive to perturbation of line impedance, and satisfies | Lg(s)‖2≤1；
wherein ,Ag＝vmg/img；Bg＝1；Cg＝-vpcc/igc；Dg＝0；
(32) Current error tracking value Ierr_abcAnd the impedance Z of the parallel linelineThrough a transfer function Lg(s) deriving a current detection error value Δ I in response to line impedance perturbationserrDeviation from the target value of current Δ Ierr *After comparison, 0 is used as the input of a stable compensator K(s); wherein Z isline＝Rline+Lline；
(33) Setting the transfer matrix of the low-pass filter W(s) to
wherein ,HupIs the passband gain of the filter; omegacα, β are coefficients of binomial equations for the cut-off frequency of the filter;
a closed loop system of adaptive controllers is shown asWherein the disturbance variablevpccIs the voltage at the PCC and is,b is the weight coefficient of the line inductance;mu is a weight coefficient output by the system, and gamma is a W(s) output parameter; the amplification matrix for a closed loop system is:
(34) based on an augmentation modelAnd (5) solving the adaptive controller through Matlab, and further performing order reduction processing to obtain a compensator transfer function K(s).
Further, perturbation parametersPrediction is performed by:
setting line impedance tracking expected value coefficient lambdaexpLine impedance tracking real-time variation value coefficient lambdarealAnd a sampling period TsB, carrying out the following steps of; h represents the coefficient of the actual value of the line impedance tracking on the coefficient lambda of the expected value of the line impedance trackingexpAnd period TsThe upper and lower floating ranges of the integral; setting the maximum prediction step length M of the controller, setting a step length variable M, and enabling M to be in the range of [1, …, M](ii) a Order toParameters are predicted for the target:
setting the prediction equation at time t +1 to wherein ,G＝λexp，
Introducing a step variable m into the prediction equation to obtain the prediction equation of the state variable at the time t + m:
wherein ,the same method can be applied for prediction.
Further, in the low-pass filter W(s), the pass-band gain H of the filterupThe coefficient of the binomial equation takes the values of α -1.4142 and β -1 respectively, and the transfer function of the obtained compensator is
Further, the harmonic compensation control module of the frequency division controller has a transfer function of wherein τp、τiProportional and integral coefficients, τ, respectivelypoFor the parallel proportion control item, s is a complex frequency domain F(s) variable, and s is a complex number, namely an s complex frequency domain; omegaoIs the fundamental angular frequency and n is the harmonic order.
Has the advantages that: compared with the prior art, the output stage power quality comprehensive compensation method based on the self-adaptive frequency division control theory is provided, under the premise that the running state of the energy storage converter is not changed, the parallel resonance controller is used for selectively compensating harmonic, reactive and unbalanced currents quickly and accurately, and output control of load current compensation components is achieved. In addition, considering nonlinear and unbalanced load access and the influence of power grid side impedance on the stability of the control system, a PCS robust self-adaptive frequency division control model under a complex power grid environment is established, and the parameter perturbation of the control system is eliminated, so that the adaptability and the anti-disturbance capability of the PCS are enhanced, and the grid-connected power quality is further improved.
Drawings
Fig. 1 is a schematic diagram of a microgrid converter structure;
FIG. 2 is a flow chart of a multi-target current compensation control method of the present invention;
FIG. 3 is a schematic block diagram of a PCS improved crossover controller of the present invention;
FIG. 4 is a diagram of an equivalent circuit structure of the grid connection of the microgrid;
fig. 5 is a schematic block diagram of an adaptive controller of the present invention.
Detailed Description
The invention is further described below with reference to the following figures and examples:
structural block diagram of microgrid converter, as shown in FIG. 1, LsIs a direct current inductance; u. ofdcIs a direct current voltage; i.e. ioIs direct current; u. ofx、ixAnd (x ═ a, b and c) represents a grid voltage and a grid current. Due to the influence of local load access on the electric energy quality at a public connection Point (PCC) of a micro-grid and a power distribution network, harmonic waves and unbalanced current components contained in grid-connected current are main factors for deteriorating the electric energy quality at the PCC, and in addition, reactive loads can also influence the power factors of grid-connected points to a certain extent. The PCS in the micro-grid compensates the power quality problem by using the residual capacity, and the energy storage converter in the micro-grid outputs power according to the instruction, wherein the control target is as follows: harmonic, reactive and three-phase unbalanced currents are quickly and accurately and selectively compensated by using the residual capacity of the PCS, and the quality of electric energy is improved.
The application discloses a grid-connected power quality compensation control method for a multifunctional energy storage converter, which comprises the following steps:
synthesizing command currentsDetecting a current Δ I to be compensated in an electrical networkabchIs compared with a grid-connected current reference value delta IabcCompounding to obtain command currentNamely, it is wherein ΔIabchIncluding reactive current, harmonic current and three-phase unbalanced current, and grid-connected current reference value delta IabcThe reference value of the grid-connected current under an ideal state is the reference value of the grid-connected current under the ideal state, namely, the reference value does not contain reactive power, harmonic waves and unbalanced current.
Generating a current tracking error Ierr_abc: detecting compensated current I with current transformerLabcComparing the command currentsAnd the output current I of the power gridLabcObtaining a current tracking error Ierr_abcI.e. by
Current tracking error signal Ierr_abcAfter passing through the frequency division controller, PWM signals are generated through a pulse width modulation technology to control the PCS. The frequency division control adopts a complex vector (CPI) control mode, namely, a Vector Proportional Integral (VPI) (transfer function) is controlled through a formula fabc＝fdqe-jωtPerforming equivalent transformation to convert abc into three-phase abc rotation coordinate system component and dq into two-phase dq static coordinate system component to obtain transfer function of complex vector control, i.e. complex vector control
In the formulae (2) and (3), τp、τiProportional and integral coefficients, GVPI(s) is a Vector Proportional Integral (VPI) controlled transfer function; gCPI(s) is a complex vector proportional integral (CPI) controlled transfer function; s is a variable of the complex frequency domain F(s), s is a complex number, i.e., the complex frequency domain s; omegaoIs the fundamental angular frequency; by comparing VPI with CPI, the VPI control ratio term τ in (3) can be knownpAnd j ωoτpThe coupled relation exists between the terms/s, which makes the independent response control of the system difficult to realize, and in order to improve the response capability, the proportional control term tau is connected in parallel on the basis of the CPI controlpoThe expression after parallel connection is as follows:
transform equation (4) in the positive and negative sequence rotation dq coordinate system to the two-phase stationary αβ coordinate system,
wherein, the superscripts +, -represent positive and negative sequences, respectively. The summation is carried out to obtain the formula (5),
equation (5) by varying the scale term τpoMake dynamicPerformance can be adjusted independently, depending on dynamic response performance, if the response speed is advanced, τ is decreasedpoIf the response is delayed, then τ is raisedpoThereby improving the PCS response performance of VPI control.
In view of the existence of random interference factors such as nonlinearity, unbalanced sensitive load and the like, the frequency division controller needs to realize stable tracking of fundamental frequency and each subharmonic frequency reference signal, and aiming at the problem, the invention introduces the self-adaptive controller in front of the frequency division controller to stabilize current error and realize control of output current.
In the microgrid interconnection equivalent circuit, v is as shown in fig. 4off f、voff nThe fundamental voltage and the harmonic voltage component are respectively generated by the droop controller; zoIs PCS equivalent output impedance; zmgIs the load in the microgrid; i.e. imgIs the current in the microgrid; i.e. ipgThe line loss current; zlineThe line impedance between the micro-grid and the grid in parallel connection; zpgo and ZpgEquivalent impedance and load on the power grid side; v. ofmg、vpcc、vpgThe middle is the alternating current bus voltage of the micro-grid, the voltage at the PCC and the voltage drop on the grid side;is the side-group wave voltage of the power grid,is the harmonic voltage at the side of the power grid; i.e. io、igc、igRespectively PCS output current, grid-connected current and power grid side current.
According to fig. 4, let PCS state variable x ═ img ig voff]T，voffThe physical meaning of (a) is the voltage generated by the droop controller; voltage v at PCCpccAnd a reference current irefAs external disturbances, iref＝Iabc *The disturbance variable w ═ iref vpcc]TI, the control variable u ═ ioThe output variable being the tracking error, i.e. y ═ Ierr_abcThen the state equation of the PCS can be expressed as
in the formula：
in the formula (6), Rmg and LmgRespectively a PCS equivalent output resistor and an inductor; rpgl＝Rpg+Rline，Lpgl＝Lpg+Lline，Rmg and LmgRespectively a PCS equivalent output resistor and an inductor; rline and LlineRespectively, line resistance and line inductance, Rpg and LpgRespectively a grid side resistor and a grid side inductor.
From the formula (6), it can be seen that the line resistance R islineOnly the perturbation of the system parameter A is caused, and the line inductance L islineThen the system parameter matrix A and the disturbance input parameter matrix B are generated1Meanwhile, perturbation occurs, so that the control strategy based on the self-adaptive basic principle is designed aiming at the change of the line impedance so as to increase the adaptability and the disturbance resistance of the PCS to treat the power quality.
Let A01＝Rpgl/Lpgl，B01＝－1/LpglWhen considering the change of the impedance on the power grid side, there are
In the formulae (7) and (8), A0Representing a constant value of the corresponding impedance, B0A constant value representing the corresponding inductive reactance can be expressed in the following standard form for perturbation portions Δ a and Δ B in equations (7) and (8)
In the formula, the first step is that,as Δ a and Δ B estimates; l isg(s) is an unknown time-varying function with Lebesque measurable elements and satisfies | | | Lg(s)||2≤1。Lg(s) can be represented as
In the formula (10), Ag＝vmg/img；Bg＝1；Cg＝-vpcc/igc；Dg＝0。
Ierr_abcThrough a transfer function Lg(s) deriving a current detection error value Δ I in response to line impedance perturbationserrDeviation from the target value of current Δ IerrAfter comparison, 0 is used as the input of the stability compensator k(s), as shown in fig. 5. The transfer matrix of the low-pass filter W(s) is set as follows
in the formula,Hup-1 is the pass band gain of the filter; omegacThe cutoff frequency of the filter is α -1.4142, and β -1 is the coefficient of the binomial equation.
The standard adaptive model obtained according to the figure 5 is used for controlling the object Fp(x) And W(s), obtaining output parameter gamma of W(s), and transfer function augmentation matrixIntroducing a system output weighting variable mu; whereinThe closed loop system can be represented as
Wherein the augmented model of the closed loop systemComprises the following steps:
based on an augmentation modelThe self-adaptive controller is solved by Matlab, and the order reduction processing is further carried out to obtain the transfer function K(s) of the compensator, namely
To eliminate control systems due to line impedanceThe method adopts a prediction identification algorithm to carry out perturbation on perturbation parametersMaking a prediction toFor the sake of example:
setting line impedance tracking expected value coefficient lambdaexpLine impedance tracking real-time variation value coefficient lambdarealAnd a sampling period TsH represents the coefficient of the actual value of the line impedance tracking on the coefficient lambda of the expected value of the line impedance trackingexpAnd period TsThe upper and lower floating ranges of the integral; if λrealThe acquisition is small enough, so that the actual value of the line impedance can closely track the expected value at each moment, the rapidity of the control system is improved, but the control system has poor robustness and anti-interference performance to the linear impedance mismatch, if lambda is used, the control system has poor robustness and anti-interference performancerealIt is taken sufficiently large that a stable control rate can be easily derived, but the dynamic response of the system will approach the natural response of the controlled object.
Setting the maximum prediction step length M of the controller, setting a step length variable M, and enabling M to be in the range of [1, …, M](ii) a Let in formula (9)Predicting a parameter for the target; setting the prediction equation at time t +1 as
wherein ,G＝λexp，
Introducing a step variable m into the prediction equation to obtain the prediction equation of the state variable at the time t + m:
wherein ,
similarly perturbation parameters can be predicted according to the method
Claims (5)
1. A grid-connected power quality compensation control method for a multifunctional energy storage converter is characterized by comprising the following steps:
(1) synthesizing the command current: detecting a current Δ I to be compensated in an electrical networkabchIs compared with a grid-connected current reference value delta IabcCompounding to obtain command currentNamely, it is wherein ΔIabchThe method comprises the following steps of (1) including reactive current, harmonic current and three-phase unbalanced current;
(2) generating a current tracking error: detecting compensated current I output by current transformerLabcComparing the command currentsAnd compensated current ILabcObtaining a current tracking error Ierr_abcI.e. by
(3) Introducing an adaptive controller to control the influence of the line impedance disturbance so as to ensure the stability of the current tracking error: based on controlled object Fp(x) And a low-pass filter W(s) for introducing a time-varying function L having an impedance elementg(s) constructing a standard self-adaptive model to obtain a stable suppressor K(s); will current tracking error Ierr_abcAnd adaptive controller output current Is_abcOf (2) synthesized current IabcThe adaptive control of the closed-loop system is realized as the input of an adaptive controller;
(4) will synthesize a current IabcThe frequency division controller is formed by connecting a plurality of specific subharmonic compensation control modules in parallel, and the compensation control modules corresponding to specific subharmonics needing to be compensated are connected in parallel to obtain a frequency division control output UPVPI；
(5) Controlling the frequency division to output UPVPIThe PWM signal is generated through a pulse width modulation technology, and the energy storage converter is controlled to inject the compensated current I into the power gridLabc。
2. The grid-connected power quality compensation control method according to claim 1, wherein the stability suppressor k(s) in step (3) is obtained by the following steps:
(31) according to the state equation of the energy storage converter, a time-varying function L with an impedance element is introducedg(s) as a transfer function in response to perturbation of line impedance:
according to the microgrid grid-connected equivalent circuit, the state equation of the energy storage converter can be expressed as:
wherein , C1＝[0 -1 0]，D1＝[0 1]，D2＝0；Rmg and LmgRespectively a PCS equivalent output resistor and an inductor; rline and LlineRespectively, line resistance and line inductance, Rpg and LpgRespectively a grid side resistance and a grid side inductance, Rpgl＝Rpg+Rline，Lpgl＝Lpg+Lline；
Let A01＝Rpgl/Lpgl，B01＝-1/LpglWhen the change of the grid side impedance is taken into account, then
in the formula,A0Representing a constant value of the corresponding impedance, B0Representing constant values of the corresponding inductive reactance, perturbation portions Δ A and Δ B, which can be expressed asWherein the perturbation parameterPredicted values for Δ A and Δ B; l isg(s) is an unknown time-varying function with Lebesque measurable elements, here as a transfer function in response to perturbation of line impedance, and satisfies | | | Lg(s)||2≤1；
wherein ,Ag＝vmg/img；Bg＝1；Cg＝-vpcc/igc；Dg＝0；
(32) Current error tracking value Ierr_abcAnd the impedance Z of the parallel linelineThrough a transfer function Lg(s) deriving a current detection error value Δ I in response to line impedance perturbationserrDeviation from the target value of current Δ Ierr *After comparison, 0 is used as the input of a stable compensator K(s); wherein Z isline＝Rline+Lline；
(33) Setting the transfer matrix of the low-pass filter W(s) to
wherein ,HupIs the passband gain of the filter; omegacα, β are coefficients of binomial equations for the cut-off frequency of the filter;
a closed loop system of adaptive controllers is shown asWherein the disturbance variablevpccIs the voltage at the PCC and is,b is the weight coefficient of the line inductance;mu is a weight coefficient output by the system, and gamma is a W(s) output parameter; the amplification matrix for a closed loop system is:
(34) based on an augmentation modelAnd (5) solving the adaptive controller through Matlab, and further performing order reduction processing to obtain a compensator transfer function K(s).
3. The grid-connected power quality compensation control method according to claim 2, wherein the perturbation parameterPrediction is performed by:
setting line impedance tracking expected value coefficient lambdaexpLine impedance tracking real-time variation value coefficient lambdarealAnd a sampling period TsB, carrying out the following steps of; h represents the coefficient of the actual value of the line impedance tracking on the coefficient lambda of the expected value of the line impedance trackingexpAnd period TsThe upper and lower floating ranges of the integral; setting the maximum prediction step length M of the controller, setting a step length variable M, and enabling M to be in the range of [1](ii) a Order toParameters are predicted for the target:
setting the prediction equation at time t +1 to wherein ,G＝λexp，
Introducing a step variable m into the prediction equation to obtain the prediction equation of the state variable at the time t + m:
wherein , the same method can be applied for prediction.
4. The grid-connected power quality compensation control method according to claim 3, wherein in the low-pass filter W(s), a pass-band gain H of the filterupThe coefficient of the binomial equation takes the values of α -1.4142 and β -1 respectively, and the transfer function of the obtained compensator is
5. The grid-connected power quality compensation control method according to claim 1, wherein a transfer function of a harmonic compensation control module of the frequency division controller is wherein τp、τiProportional and integral coefficients, τ, respectivelypoFor parallel proportional control terms, s is a complex frequency domain F(s) variable, s is a complex number, i.e. s is a complex numberA frequency domain; omegaoIs the fundamental angular frequency and n is the harmonic order.
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