CN107732973A - For the inverter low voltage traversing control method of weak net distal end fatal voltage failure - Google Patents
For the inverter low voltage traversing control method of weak net distal end fatal voltage failure Download PDFInfo
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- H02J3/382—
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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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
- 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
- H02J3/50—Controlling the sharing of the out-of-phase component
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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
- Y02E40/30—Reactive power compensation
Abstract
The invention discloses a kind of inverter low voltage traversing control method for weak net distal end fatal voltage failure.When weak net distal end fatal voltage failure occurs, watt current control targe amount and reactive current control aim parameter are switched to zero in inverter, then watt current control targe amount and the input of reactive current control aim parameter of inverter are designed, carry out transient state transition, and optimize phaselocked loop, current inner loop and electric voltage feed forward parameter, inverter stability and dynamic control performance when improving low voltage crossing.The present invention is avoided that inverter unstability when fatal voltage falls failure occurs for weak distal end off the net, inverter end voltage can effectively be recovered and inverter is injected certain active power for supporting mains frequency, can be applied to it is weak it is off the net using inverter as interface new energy power station grid-connected system distal end occur fatal voltage failure when, realize inverter system low voltage crossing.
Description
Technical Field
The invention relates to the technical field of electrical information, in particular to a low-voltage ride through control method of an inverter aiming at a remote severe voltage fault of a weak grid.
Background
With the access of a large amount of power generated by renewable energy sources such as photovoltaic energy, wind energy and the like to a power system, low-voltage ride-through capability is provided for the power generation grid connection of the renewable energy sources at home and abroad. In addition, during the voltage drop, the grid-connected guide rules require that a wind power plant and a photovoltaic power station inject reactive current in a certain proportion to the voltage drop to support the voltage of a power grid, and the residual capacity is sent out in an active mode to prevent the power grid from generating large active shortage to influence the frequency stability of the system.
Grid-connected guidance generally assumes that an alternating current power grid is a strong grid (i.e., a line inductance value is small), and requires that an inverter has a certain low-voltage ride-through capability. However, renewable energy grid connection in China has the characteristics of long distance, large scale and high concentration, and a weak power grid (namely a large line inductance value) is usually arranged on the power grid side. Different from a voltage drop fault at a near-end public connection point in a strong network, when the voltage drop fault occurs at a far-end power grid side in a weak power grid, the voltage drop at the end of an inverter is small under the influence of a high inductive reactance value of a line, and a typical low-voltage ride-through control strategy possibly has an inapplicable risk, so that the inverter has a new instability problem.
At present, researches on a low voltage ride through process of an inverter mainly focus on small interference stability analysis and static stability analysis, and few researches are conducted on designing a low voltage ride through control method suitable for a weak grid under the condition of a far-end serious voltage drop fault of an inverter system.
Disclosure of Invention
In order to solve the problems, the invention provides an inverter low-voltage ride-through control method aiming at the serious voltage fault of the far end of the weak grid, which can effectively recover the voltage of the inverter end and enable the inverter to inject certain active power for supporting the grid frequency.
The technical scheme of the invention comprises the following steps:
when a serious voltage fault occurs at the far end of the weak network, the active current in the inverter is controlled to a target value I dref And a reactive current control target amount I qref Switching to zero, and designing the control target quantity I of the active current of the inverter dref And a reactive current control target amount I qref And inputting, performing transient transition, optimizing phase-locked loop, current inner loop and voltage feedforward parameters, and improving the stability and dynamic control performance of the inverter during low voltage ride through.
In the invention, when the voltage of the far end of the weak network drops to 0.2p.u. The low voltage ride through is voltage ride through aiming at the weak network far end severe voltage fault scene.
The active current control target quantity I of the inverter is designed dref And a reactive current control target amount I qref Inputting, and performing transient transition, specifically:
firstly, obtaining a reactive current amplitude reference value I 'by utilizing integral control' qref So as to realize the adjustment of the terminal voltage without difference and obtain the equivalent voltage E and the equivalent impedance X of the alternating current power grid by utilizing the recursive least square method for identification ∑ And calculating to obtain an active current amplitude reference value I' dref ；
Then, adopting a discrete active disturbance rejection controller to carry out reactive current amplitude reference value I' qref And an active current amplitude reference value I' dref Processing to obtain active current control target quantity I for input inverter dref And a reactive current control target amount I qref To implement a transient transition process.
Obtaining a reactive current amplitude reference value I 'by utilizing integral control' qref Specifically, the following formula is adopted:
I′ qref ＝∫k i (V t -V tref )dt
wherein k is i Is an integral coefficient, I' qref For inverterReference value of input reactive current amplitude, V t To the inverter terminal voltage, V tref For reference to terminal voltage, in particular implementations 0.9pu, t represents time.
The method for identifying and obtaining the equivalent voltage E and the equivalent impedance X of the alternating current power grid by using the recursive least square method ∑ And calculating to obtain an active current amplitude reference value I' dref The following method is specifically adopted:
1) Establishing equivalent voltage E and equivalent impedance X of alternating current power grid ∑ The equality relationship between:
V td ＝V t ＝E-X ∑ I q
wherein, V td Is d-axis voltage component of inverter terminal voltage, E is equivalent voltage of AC network, X ∑ For equivalent inductive reactance of the AC mains, I q Is the q-axis current component of the filter inductor;
2) Calculating a parameter vector theta (t) to be solved at the t moment by adopting the following formula:
in the formula, theta (t) is a parameter vector to be solved at the moment t, and theta (t) = [ EX = [ (-) ] ∑ ] T (ii) a Theta (t-1) is a parameter vector at the t-1 moment; y (t) is an output vector at the time t, and y (t) is equal to the voltage component V of the inverter terminal d axis at the time t td I.e. y (t) = V td (t)，V td (t) V at time t td ，V td Obtained by adopting the calculation of the step 1) above,for the measurement vector at the time t,I q (t) represents the filter inductance q-axis current component at time t, I d (t) represents the d-axis current component of the filter inductor at time t, I d (t-1) represents a d-axis current component of the filter inductor at the time of t-1; p (t) is an inverse matrix of the covariance at time t; when P (t-1) is t-1Etching an inverse matrix of the covariance;
in the formula I d (t)-I d (t-1) is an additional perturbation term used to speed up the algorithm convergence speed so that the term converges rapidly to 0.
3) When a severe voltage drop fault occurs, identification is triggered.
If the parameter vector theta (t) to be solved does not satisfy max (theta (t) -theta (t-1) }<1e -3 Repeating the step 2) to perform recursive calculation;
if the parameter vector theta (t) to be solved meets max (theta (t) -theta (t-1) }<1e -3 Outputting a parameter vector theta (t) to be solved as an identification result, and obtaining the equivalent voltage E and the equivalent inductive reactance X of the alternating current power grid in the identification result ∑ ；
4) Calculating an active current amplitude reference value I 'by adopting the following formula' dref ：
I′ dref ＝0.8E/X ∑ 。
In specific implementation, the maximum allowable injection value I of the d-axis current component of the network side line inverter dmax Comprises the following steps:
I dmax ＝E/X ∑ 。
the discrete active disturbance rejection controller is adopted to carry out reactive current amplitude reference value I' qref And an active current amplitude reference value I' dref Processing to obtain active current control target quantity I for input inverter dref And a reactive current control target amount I qref The following method is specifically adopted:
first, a discrete type active disturbance rejection controller of the following formula is established:
wherein v is 1 (t) is the output of the discrete active disturbance rejection controller, i.e. the expected track; v. of 2 (t) is v 1 (t), h represents the sampling step size, t represents the t-th time in h, r isAn amplitude limit; r is a radical of hydrogen 0 And h 0 Are respectively a controller fhan (v) 1 (t)-v(t),v 2 (t),r 0 ,h 0 ) The internal gain parameter and step parameter, v (t) is the output of the discrete type active disturbance rejection controller, i.e. v 1 (t) a desired value; fhan (v) 1 (t)-v(t),v 2 (t),r 0 ,h 0 ) And (3) representing the fastest control comprehensive function, specifically adopting book active disturbance rejection control technology: method page 69 of estimate controls to compensate for uncertainty factors.
The discrete active disturbance rejection controller of the invention autonomously designs a smooth transition process, and solves the problem of overshoot which may occur in reference point tracking.
Then, the inverter injects an active current control target quantity I dref And a reactive current control target amount I qref And (3) transition process: reference value I 'of active current amplitude' dref As input v (t), i.e. v (t) = I ', of a discrete type active disturbance rejection controller' dref (t) the output processed by the discrete type active disturbance rejection controller is an active current control target quantity I dref I.e. I dref (t)＝v 1 (t); reference value I 'of reactive current amplitude' qref As an input v ' (t) to another discrete type active disturbance rejection controller, i.e. v ' (t) = I ' qref (t), output v 'processed by discrete type active disturbance rejection controller' 1 (t) as a control target amount I of reactive current injected into the inverter qref I.e. I qref (t)＝v′ 1 (t)。
The phase-locked loop frequency band reduction helps to improve the system damping at low voltage ride through, but this results in poor phase-locked loop phase-locking effect. Considering that when a serious low-voltage fault occurs, the voltage of the inverter at the initial stage may oscillate due to sudden change of the voltage at the far end, and the damping of a system should be mainly improved; when the voltage of the inverter terminal is restored to a certain degree, the system stability is improved to a certain extent along with the injection of reactive current, and the performance of the phase-locked loop can be improved mainly.
The phase-locked loop and the currentThe loop and voltage feedforward parameters include the phase-locked loop integral coefficient k i_pll And the proportionality coefficient k p_pll Integral coefficient of inner loop of current k i_acc And the proportionality coefficient k p_acc Voltage feedforward coefficient a f Specifically, the following method is adopted for optimization:
a) Self-adaptive optimization phase-locked loop parameters: using inverter terminal voltage amplitude signal V t The phase-locked loop parameters are optimized in real time by adopting the following formula:
in the formula: i V t I is the absolute value of terminal voltage amplitude, k p_pll 、k i_pll Are respectively a phase-locked loop proportional coefficient and an integral coefficient k 'before optimization' p_pll 、k′ i_pll Respectively obtaining an optimized phase-locked loop proportional coefficient and an optimized integral coefficient;
by the formula optimization, the bandwidth of the phase-locked loop can be reduced at the initial stage of voltage fault, the system damping is increased, the stability of the inverter system at the initial stage of fault is improved, and meanwhile, in the voltage recovery process, the bandwidth of the phase-locked loop is gradually increased, the tracking speed of the phase-locked loop is improved, and the dynamic performance is improved.
b) Optimizing current inner loop parameters: adjusting the current inner loop proportionality coefficient k p_cc And integral coefficient k i_acc The current inner loop frequency band is within the range of 300 Hz-350 Hz;
c) Optimizing voltage feedforward link parameters: reducing voltage feedforward loop parameter a f To between 0.002 and 0.1.
The invention has the beneficial effects that:
the method can avoid the instability of the inverter when the remote end under the weak grid has serious voltage drop fault, can effectively recover the voltage of the inverter end and enables the inverter to inject certain active power for supporting the grid frequency, and can be applied to the remote end of a new energy power station grid-connected system taking the inverter as an interface under the weak grid to realize the low-voltage ride through of the inverter system when the remote end has serious voltage fault.
Drawings
Fig. 1 is a block diagram and equivalent circuit of a typical low voltage ride through control for an inverter of the present invention.
Fig. 2 is a block diagram of an improved low voltage control strategy for an inverter of the present invention.
FIG. 3 is a block diagram of the calculation flow of the recursive least squares algorithm of the present invention.
FIG. 4 shows an example of X in the simulation verification of the present invention ∑ And an inverter terminal voltage response curve when =0.8pu, k =4, e = 0.2pu.
Fig. 5 is a response curve of inverter terminal voltage and output active power when the proposed novel low voltage ride through control strategy is adopted in simulation verification according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
The principle of the invention is as follows:
a typical low voltage ride through control strategy of the inverter and its structure are shown in fig. 1, and the definitions and physical meanings of some variables are shown in table 1 below. The Low Voltage Ride-Through (LVRT) control strategy comprises the following steps: the current control link and the current dq axis control target quantity. The values of the main parameters of the system are shown in table 2.
TABLE 1 symbolic definition and description of partial system variables in the drawings of the present invention
A current control link dynamic mathematical model:
in the formula: the first term on the right side of the equation is a conventional current inner loop PI control link, the second term on the right side of the equation is a current feedforward compensation term, and the third term on the right side of the equation is voltage feedforward.
The current dq axis control target amount is:
in the formula: i is qref0 Control target quantity, V, for q-axis current in pre-fault control mode t Is the inverter terminal voltage amplitude, k is the gain factor,upper limit of d-axis current control target amount, I max The inverter current capacity (taken as 1.22pu here without loss of generality).
Table 2 Simulink simulation parameters
| Rated voltage/V of system | 380 |
| Rated frequency/Hz of system | 50 |
| System rated capacity/kVA | 10 |
| Filter inductance L f /pu | 0.15 |
| Filter capacitor C f /pu | 0.05 |
| Damping resistor R d | 0.1 |
| Current inner loop parameter k p_acc 、k i_acc | 1、15 |
| Phase-locked loop parameter k p_pll 、k i_pll | 80、3500 |
| Feed forward gain coefficient a f | 40 |
The new low voltage control method provided by the invention is an improvement on the basis of a typical low voltage ride through control strategy, and as shown in fig. 2, the specific improvement comprises the following steps:
1) Changing the q-axis current control target amount I qref . When a remote severe voltage drop fault occurs, the q-axis current control target amount becomes 0. Generating inverter injection reactive current amplitude reference value I 'through an integration link' qref ，I′ qref Generating a q-axis current control target quantity I through a discrete active disturbance rejection controller qref . The specific implementation steps comprise:
firstly, generating an inverter injection reactive current amplitude reference value I 'through an integration link' qref The following formula:
I′ qref ＝∫k i (V t -V tref )dt (4)
in the formula, k i Is an integral systemNumber, here taken as 5,V t Inverter terminal voltage, V tref For reference terminal voltage, 0.9pu is chosen here. Integral control is used to achieve a dead regulation of the terminal voltage.
The discrete type active disturbance rejection controller has the following specific formula:
wherein v is 1 (t) referred to as the desired trajectory, i.e. the output of the controller, v 2 (t) is v 1 (t) a derivative of; h represents a sampling step size; t represents the t-th time with h as a time interval; r is an amplitude limiting amplitude; r is 0 ，h 0 Is a controller internal parameter; v (t) is v 1 (t) desired value, i.e. input to the controller, where let v (t) = I' qref ；fhan(v 1 (t)-v(t),v 2 (t),r 0 ,h 0 ) Representing the steepest control synthesis function.
2) Changing d-axis current control target quantity I dref . When a remote severe voltage drop fault occurs, the d-axis current control target amount becomes 0. By identifying the equivalent voltage E and the equivalent inductive reactance X of the remote power grid ∑ Determining the maximum allowable value I of the injection current of the d-axis of the inverter dmax Designing an inverter injection active current amplitude reference value I' dref ，I′ dref Generating a d-axis current control target quantity I through a discrete active disturbance rejection controller dref . The specific implementation steps comprise:
firstly, the equivalent voltage E and the equivalent inductive reactance X of the remote power grid need to be identified ∑ . Making certain assumptions to obtain equivalent voltage E and equivalent inductive reactance X ∑ The equation of (c).
Assume that 1: when a serious voltage drop fault occurs, the inverter is rapidly switched to a low voltage ride through mode, the d-axis reference current is switched to 0, and the q-axis reference current is jointly determined by equation (4) and equation (5);
assume 2: on the premise of hypothesis 1, ignoring the dynamic time scale of the current inner loop, enabling the d-axis current and the q-axis current of the filter inductor to be approximately equal to the reference values, and rapidly converging the d-axis current of the filter inductor and the equivalent inductor at the network side to 0 (a large amount of simulation finds that the simulation result conforms to hypothesis 2);
assume that 3: because the filter capacitor is relatively small, the d-axis current and the q-axis current on the filter inductor are approximately equal to the d-axis current and the q-axis current on the equivalent inductor on the network side in a dynamic state.
Under the quasi-steady state premise, the network side line has an equality relation:
wherein, I do And I qo D-axis current and q-axis current flowing through the network side respectively; x ∑ Equivalent inductive reactance of a network side; e d And E q The components of the equivalent voltage on the network side are respectively on the d axis and the q axis.
Based on assumptions 1 and 3, equation (6) is reduced to:
V td ＝V t ＝E-X ∑ I q (7)
the above equation (7) represents the equivalent voltage E on the network side and the equivalent reactance X on the line ∑ Approximate equality of (c).
The method adopts a recursive least square method to identify the equivalent voltage E and the line equivalent reactance X ∑ The algorithm only needs to collect the d-axis component V of the local information inverter terminal voltage td And a filter inductance q-axis current component I q 。
In a specific implementation, the initial values are: θ (0) = [0 1 =] T P (0) = diag {100 }, and the sampling period is set to 0.005s. When a serious voltage drop fault occurs, triggering identification, and when a parameter vector theta (t) to be solved meets max { theta (t) -theta (t-1) }<1e -3 Then, the output θ (t) is the recognition result. The specific identification steps are shown in FIG. 3.
Specifically, an injected active current amplitude reference value I 'is taken' dref Comprises the following steps:
I′ dref ＝0.8E/X ∑ (8)
injecting d-axis current amplitude reference value I' dref As the input of a discrete active disturbance rejection controller (5), the output of the discrete active disturbance rejection controller is the reference value I of the injection current of the d axis of the inverter dref 。
3) And phase-locked loops, current inner loops and voltage feedforward coefficients are optimized. The phase-locked loop parameter self-adaptive adjustment is carried out by adopting the following formula:
secondly, optimizing current inner loop parameters: selecting the current inner ring proportion parameter as k p_acc =1 and an integration parameter of k i_acc ＝15。
And finally, optimizing the parameters of a voltage feedforward link: reducing voltage feedforward link parameter a f And the small interference stability of the system is improved and is set to be 0.002.
The specific embodiment of the invention is as follows:
to verify the validity of the proposed control strategy, the system shown in fig. 1 was simulated in a MATLAB/Simulink environment. The normal control mode of the inverter is an active/alternating voltage control mode, and the system stably runs at P before a fault e =0.6pu and V t A far-end voltage drop fault occurs when =1pu, t = 3s. The main parameters are detailed in table 3.
FIG. 4 shows the line impedance X ∑ And =0.8pu, a gain coefficient k =4, and a voltage sag degree E =0.2 pu. It can be seen from fig. 4 that the voltage at the inverter terminal oscillates up and down around 0.9pu, which causes the inverter control mode to switch back and forth between the pre-fault control mode and the typical low voltage control mode, and the inverter is unstable.
FIG. 5 shows an inverter with the low voltage ride through control method of the present invention, in line impedance X ∑ And when the voltage drop degree is E =0.2pu, the inverter terminal voltage and the output active power waveform response curve are obtained. When t =10.08s, the recursive least square method converges and is identifiedE ≈ 0.17pu and X ≈ 0.67pu from' dref And (4) the current reference value of the d-axis of the inverter is triggered to be switched to be output by the discrete active disturbance rejection controller when the current reference value is approximately equal to 0.20 pu. As can be seen from fig. 5, during the fault, the inverter terminal voltage returns to the specified value of 0.9pu, and the inverter injects 0.18pu of active power into the grid, illustrating the effectiveness of the proposed control method.
The inverter low voltage ride through control method for the severe voltage fault at the far end of the weak grid according to the present invention is described in detail above, and the principle and the implementation manner of the present invention are illustrated herein by using specific examples, and the above description of the embodiments is only used for explaining the method and the core idea of the present invention, but not limiting the present invention, and any modifications and changes made to the present invention within the spirit of the present invention and the scope of the claims fall within the scope of the present invention.
Claims (6)
1. A low voltage ride through control method of an inverter aiming at a remote severe voltage fault of a weak network is characterized by comprising the following steps: when a serious voltage fault occurs at the far end of the weak network, the active current in the inverter is controlled to a target value I dref And a reactive current control target amount I qref Switching to zero, and designing the active current control target quantity I of the inverter dref And a reactive current control target amount I qref And inputting, performing transient transition, optimizing phase-locked loop, current inner loop and voltage feedforward parameters, and improving the stability and dynamic control performance of the inverter during low voltage ride through.
2. The inverter low voltage ride through control method for the weak grid remote severe voltage fault according to claim 1, characterized in that: the design inverter active current control target quantity I dref And a reactive current control target amount I qref Inputting, and performing transient transition, specifically:
firstly, obtaining a reactive current amplitude reference value I 'by utilizing integral control' qref And meanwhile, identifying and obtaining the equivalent of the alternating current power grid by using a recursive least square methodVoltage E and equivalent impedance X ∑ And calculating to obtain an active current amplitude reference value I' dref ；
Then, adopting a discrete active disturbance rejection controller to carry out reactive current amplitude reference value I' qref And an active current amplitude reference value I' dref Processing to obtain active current control target quantity I for input inverter dref And a reactive current control target amount I qref 。
3. The inverter low voltage ride through control method for the weak grid remote severe voltage fault according to claim 2, characterized in that: obtaining a reactive current amplitude reference value I 'by utilizing integral control' qref Specifically, the following formula is adopted:
I′ qref ＝∫k i (V t -V tref )dt
wherein k is i Is an integral coefficient, I' qref Injecting a reactive current amplitude reference value, V, for the inverter t To the inverter terminal voltage, V tref To refer to the terminal voltage, t represents time.
4. The inverter low voltage ride through control method for the weak grid remote severe voltage fault according to claim 2, characterized in that: the method for identifying and obtaining the equivalent voltage E and the equivalent impedance X of the alternating current power grid by using the recursive least square method ∑ And calculating to obtain an active current amplitude reference value I' dref The following method is specifically adopted:
1) Establishing equivalent voltage E and equivalent impedance X of alternating current power grid ∑ The equality relationship between:
V td ＝V t ＝E-X ∑ I q
wherein, V td Is d-axis voltage component of inverter terminal voltage, E is equivalent voltage of AC network, X ∑ For equivalent inductive reactance of the AC mains, I q Is the q-axis current component of the filter inductor;
2) Calculating a parameter vector theta (t) to be solved at the t moment by adopting the following formula:
in the formula, theta (t) is a parameter vector to be solved at the moment t, and theta (t) = [ EX = [ (-) ] ∑ ] T (ii) a Theta (t-1) is a parameter vector at the t-1 moment; y (t) is an output vector at the moment t, and y (t) is equal to the d-axis voltage component V of the inverter terminal voltage at the moment t td I.e. y (t) = V td (t)，V td (t) V at time t td ，For the measurement vector at the time t,I q (t) represents the filter inductance q-axis current component at time t, I d (t) represents the d-axis current component of the filter inductor at time t, I d (t-1) represents a d-axis current component of the filter inductor at the time of t-1; p (t) is an inverse matrix of the covariance at time t; p (t-1) is an inverse matrix of the covariance at the time t-1;
3) If the parameter vector theta (t) to be solved does not satisfy max (theta (t) -theta (t-1) }<1e -3 Repeating the step 2) to carry out recursion calculation;
if the parameter vector theta (t) to be solved meets max { theta (t) -theta (t-1) }<1e -3 Outputting a parameter vector theta (t) to be solved as an identification result, and obtaining the equivalent voltage E and the equivalent inductive reactance X of the alternating current power grid in the identification result ∑ ；
4) Calculating an active current amplitude reference value I 'by adopting the following formula' dref ：
I′ dref ＝0.8E/X ∑ 。
5. The inverter low voltage ride through control method for the weak grid far-end severe voltage fault according to claim 2, characterized in that: the discrete active disturbance rejection controller is adopted to carry out reactive current amplitude reference value I' qref And an active current amplitude reference value I' dref Processing to obtain active current control target quantity I for input inverter dref And a reactive current control target amount I qref The following method is specifically adopted:
first, a discrete type active disturbance rejection controller of the following formula is established:
wherein v is 1 (t) is the output of the discrete-type active disturbance rejection controller, v 2 (t) is v 1 (t) the derivative of (t), h represents the sampling step, t represents the t-th time interval with h, and r is the amplitude of the amplitude limiter; r is 0 And h 0 Are respectively a controller fhan (v) 1 (t)-v(t),v 2 (t),r 0 ,h 0 ) Internal gain parameters and step parameters, v (t) is the output of the discrete active disturbance rejection controller; fhan (v) 1 (t)-v(t),v 2 (t),r 0 ,h 0 ) Representing the steepest control synthesis function.
Then, the active current amplitude value is referenced to value I' dref The output processed by the discrete type active disturbance rejection controller is used as the input v (t) of the discrete type active disturbance rejection controller as the active current control target quantity I dref (ii) a Reference value I 'of reactive current amplitude' qref As an input v ' (t) of another discrete type active disturbance rejection controller, an output v ' processed by the discrete type active disturbance rejection controller ' 1 (t) as a control target amount I of the inverter-injected reactive current qref 。
6. The inverter low voltage ride through control method for the weak grid far-end severe voltage fault according to claim 1, characterized in that: the phase-locked loop, the current inner loop and the voltage feedforward parameter comprise phase-locked loop integral coefficient k i_pll And the proportionality coefficient k p_pll Integral coefficient of inner loop of current k i_acc And the proportionality coefficient k p_acc Voltage feedforward coefficient a f The following method is specifically adopted for optimization:
a) Self-adaptive optimization of phase-locked loop parameters: using the inverseLevel of transformer terminal voltage amplitude signal V t The phase-locked loop parameters are optimized in real time by adopting the following formula:
in the formula: | V t I is the absolute value of terminal voltage amplitude, k p_pll 、k i_pll Are respectively a phase-locked loop proportional coefficient and an integral coefficient k 'before optimization' p_pll 、k′ i_pll Respectively obtaining an optimized phase-locked loop proportional coefficient and an optimized integral coefficient;
b) Optimizing current inner loop parameters: adjusting the current inner loop proportionality coefficient k p_cc And integral coefficient k i_acc The current inner loop frequency band is within the range of 300Hz to 350 Hz;
c) Optimizing voltage feedforward link parameters: reducing voltage feedforward loop parameter a f To between 0.002 and 0.1.
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