CN115940683A - Photovoltaic grid-connected inverter control method based on improved sliding mode control - Google Patents
Photovoltaic grid-connected inverter control method based on improved sliding mode control Download PDFInfo
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Abstract
The invention belongs to the technical field of inverter control, and particularly relates to a photovoltaic grid-connected inverter control method based on improved sliding mode control. Aiming at the problem that the control performance of the photovoltaic grid-connected inverter is influenced by uncertainty of a direct current side and a grid side, the direct current side voltage is selected as a state variable by an outer ring, and the steady-state error of the system is reduced by adopting integral sliding mode control; based on the influence of an approach law function on the control characteristic of the system, a novel approach law is introduced into the inner ring sliding mode control, and buffeting is weakened. Simulation analysis is carried out on an MATLAB/Simulink platform, and results show that the dynamic performance of the system is effectively improved, the harmonic distortion rate of the network access current is reduced and the system can keep strong anti-interference capability while the photovoltaic power generation system is stably operated by the proposed control strategy.
Description
Technical Field
The invention belongs to the technical field of inverter control, and particularly relates to a photovoltaic grid-connected inverter control method based on improved sliding mode control.
Background
In recent years, in order to solve the problem of environmental deterioration caused by fossil energy, it has become common knowledge at home and abroad to fully utilize renewable energy; renewable energy grid-connected power generation represented by solar energy and wind energy has become a development trend of a novel power system.
With the improvement of photovoltaic power generation efficiency and the increase of grid-connected capacity, the influence of the control performance of the photovoltaic inverter on the power quality of a power grid is more and more obvious, and the research of the control strategy of the photovoltaic inverter has important significance on the development of a novel power system.
Although the traditional inverter control method, such as linear control modes of constant voltage and constant frequency control, constant power control, droop control and the like, can realize good control on the inverter, the traditional inverter control method has poor inhibition effect on external interference and insufficient robustness.
In order to solve the above problems, various nonlinear control methods are applied to the inverter control. The research of the H-infinity robust control strategy of the photovoltaic grid-connected inverter considers uncertain parameters of the inverter and power grid interference, designs a current loop H-infinity robust controller, but does not consider the control performance of a voltage outer loop and the stability of direct-current side voltage. The robust H-infinity control technology and the active disturbance rejection control of the photovoltaic grid-connected inverter based on the double closed-loop strategy are combined, the robust double-loop control strategy based on the grid voltage orientation is provided, and the tracking error caused by external disturbance is effectively inhibited; however, the design of the controller parameters is complex and depends heavily on the accuracy of the system model. "Aourri M, aboulfia, lachkar I, et. Nonlinear control and stability analysis of single stage grid connected photovoltaic Systems [ J ]. International Journal of electric Power & Energy Systems,2020,15 (10): 1-15." combining the backstepping method with the PI controller, a nonlinear controller is designed to achieve the Power balance between the grid and the photovoltaic system, but does not consider the influence of external disturbances such as grid voltage fluctuation.
The photovoltaic grid-connected inverter is a periodic variable structure system. The Sliding Mode Control (SMC) strategy is suitable for controlling a photovoltaic grid-connected inverter because of its strong robustness. "Sebaale F, vaheid H, kanaan H Y, et al sliding mode fixed frequency current controller design for grid-connected NPC inverter [ J]IEEE Journal of electronic and Selected diagnostics in Power Electronics,2016,4 (4): 1397-1405, "designs a suitable applicationA current loop sliding mode controller of a neutral point clamping type three-level inverter is adopted, but a voltage loop of the current loop sliding mode controller is still controlled by a PI (proportional integral) mode, so that the anti-disturbance capability is limited. "
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B.Discrete-time sliding mode direct power control for three-phase grid connected multilevel inverter[C]I/4 th International Conference on Power engineering, energy and electric drives, IEEE,2013, 933-938, "a discrete sliding mode direct Power control strategy is provided according to the principle of minimum active and reactive errors, but the phenomenon of 'buffeting' in the control process is not considered. "Liuy, zhang Q, wang C, et al.A. control strategy for micro inverters based on adaptive three-order sliding mode and optimized drop control [ J]Electric Power Systems Research,2014,117 "combine sliding mode control with an adaptive observer to attenuate buffeting by adjusting the coefficients of the system switching function, but do not specify an adaptive observer for online adjustment of the sign function system.
In summary, aiming at the problem that uncertain interference exists on the direct current side and the network side of the photovoltaic grid-connected inverter, the invention provides a double-closed-loop sliding mode control strategy which comprises the following steps: the voltage outer ring is controlled by adopting an integral sliding mode so as to reduce the steady-state error of the system while stabilizing the voltage at the direct current side; a novel approach law is provided for a current inner loop sliding mode controller, so that system buffeting is weakened as much as possible while the response speed of the system is not sacrificed.
Disclosure of Invention
Aiming at the problem that the control performance of the photovoltaic grid-connected inverter is influenced by uncertainty of a direct current side and a network side, the photovoltaic grid-connected inverter control method based on the improved sliding mode control is provided, and is an improved double-closed-loop sliding mode control strategy. The outer ring selects direct current side voltage as a state variable, and adopts integral sliding mode control to reduce the steady-state error of the system; based on the influence of an approach law function on the control characteristics of the system, a novel approach law is introduced into the inner ring sliding mode control, and buffeting is weakened. Simulation analysis is carried out on an MATLAB/Simulink platform, and results show that the dynamic performance of the system is effectively improved, the harmonic distortion rate of the network access current is reduced and the system can keep strong anti-interference capability while the photovoltaic power generation system is stably operated by the proposed control strategy.
In order to achieve the purpose, the invention adopts the following technical scheme:
a photovoltaic grid-connected inverter control method based on improved sliding mode control comprises the following steps:
step 1, expressing a mathematical model of the photovoltaic grid-connected inverter by using a dq rotating coordinate system:
in the formula u d ＝U dc S d ，u q ＝U dc S q ；S d 、S q D and q-axis components of the switching function, respectively; u. of sd 、u sq The components of the grid voltage on d and q axes are respectively; i.e. i d 、i q The components of the current on the alternating current side of the inverter on d and q axes are respectively; i.e. i L Is the current flowing into the inverter; l and R respectively represent the equivalent inductance and the internal resistance of the filter inductance at the AC side of the inverter; c and U dc Respectively representing the direct current side capacitance and voltage of the inverter; ω represents angular frequency;
step 2, the DC side voltage U of the inverter dc And a reference voltage U dc * After comparison, obtaining a d-axis reference value i of the current inner ring through the voltage outer ring d * The result obtained by the current inner loop is converted by inverse Park to obtain a control signal u α 、u β 。
Further, in the step 2, the voltage outer ring selects a direct-current side voltage as a control quantity, and the voltage outer ring sliding mode controller adopts integral sliding mode control, which specifically comprises the following steps:
selecting direct current side voltage as a control quantity, and defining the tracking error of a voltage outer ring sliding mode controller as follows:
e＝U dc * -U dc (3)
the derivative of the tracking error is then:
introducing an integral sliding mode surface:
using an exponential approximation law to make
And (5) combining the formulas (4) and (6) to obtain the sliding mode control rate of the voltage outer ring as follows:
in the formula, epsilon>|d 3 |；k>0; kS is an exponential approximation term, and lambdae is a proportion term; epsilon sgn (S) is an isokinetic approach term; i.e. i L and/C is a control item influenced by system parameters.
Further, in the step 2, the current inner ring selects the output current of the inverter as a control quantity, and a novel approach law is introduced into the current inner ring sliding mode controller, specifically:
selecting the output current of the inverter as a control quantity, and defining the tracking error of the current inner loop sliding mode controller as follows:
in the formula i q * ＝0；
The sliding mode surface of the current inner ring sliding mode controller adopts the following steps:
in the formula, c 1 、c 2 The convergence speed of the tracking error of the current inner ring sliding mode controller is shown, and the tracking error converges an index to 0 under the sliding mode surface;
when the DC side voltage of the inverter is stabilized, consider i d * The constant is obtained by combining the vertical type (10) and the formula (11), and the obtained sliding mode surface is as follows:
combining formula (1) and formula (12):
when the system is in a steady state,
in this case, the formula (1) gives:
combining equations (13) and (14) to obtain a simplified slip form surface:
the following approach law was used:
in the formula, k 1 To approach the coefficient of term constant, k 2 Is an exponential approximation term coefficient, k 1 、k 2 Characterization systemThe approach speed and the buffeting degree of the system state reaching the switching surface are n =1,2; alpha and beta are positive control parameters and are exponential terms of absolute values of tracking errors;
the combined vertical type (1), (15) and (16) obtains the current inner ring sliding mode control rate as follows:
in the formula, constant k 12 、k 22 Is an exponential approximation term coefficient, k 11 、k 21 For constant velocity approach term coefficient, alpha 1 、α 2 、β 1 、β 2 In (0, 2)]Take the constant value inside.
Further, a method for verifying the stability of the voltage outer loop sliding mode controller specifically includes:
s1, considering the influence of the uncertain external interference on the system, the formula (1) is rewritten as follows:
in the formula (d) 1 、d 2 The item represents uncertain disturbance of power grid voltage fluctuation caused by system parameter perturbation and load change; cd [ Cd ] 3 The term represents uncertain disturbance of the direct current side of the inverter caused by capacitance tolerance and illumination intensity variation;
s2, defining a Lyapunov function
Adopts generalized sliding mode condition>
Verification of stability, i.e.
Demonstration of the binding formulae (2), (7)
From the formula (9), in ∈>|d 3 |、k>Under the condition of 0, the voltage outer ring sliding mode controller meets the sliding mode stability condition.
Further, a method for verifying the stability of the current inner loop sliding mode controller specifically comprises the following steps:
s1, considering the influence of the uncertain external interference on the system, the formula (1) is rewritten as follows:
in the formula, d 1 、d 2 The item represents uncertain disturbance of power grid voltage fluctuation caused by system parameter perturbation and load change; cd [ Cd ] 3 The term represents uncertain disturbance of the direct current side of the inverter caused by capacitance tolerance and illumination intensity variation;
s2, d-axis component stability analysis of the current loop sliding mode control rate:
defining a Lyapunov function
Then
Demonstration of the binding formulae (2), (17)
The q-axis component stability analysis of the current loop sliding mode control rate and the d-axis component stability analysis of the current loop sliding mode control rate are in the same way;
from the formula (19), in k 12 >|d n |、k 22 >|d n |、k 11 >0、k 21 >Under the condition of 0, the current inner ring sliding mode controller meets the sliding mode stability condition.
Compared with the prior art, the invention has the following advantages:
the invention provides an improved double-closed-loop sliding mode control strategy by considering the uncertain interference of a direct current side and a network side in a photovoltaic grid-connected system. Through simulation experiments, the strategy of the invention is compared and analyzed with the traditional inverter control strategy, and the main conclusion obtained is as follows:
(1) The provided control strategy performs feedback control on the network access current through current inner ring sliding mode control, realizes the sine of the network access current and unit power factor grid connection, and realizes the voltage stabilization of the direct current side through voltage outer ring sliding mode control. The dynamic and steady-state performance of the system is effectively improved by improving the approximation rule and the sliding mode surface and introducing an integral link.
(2) Aiming at the problem of uncertain interference in the outside world, a novel approach law is introduced into the current inner ring sliding mode controller, and system buffeting is weakened through the high-gain characteristic of the current inner ring sliding mode controller when the system state is far away from a switching surface, so that the system obtains better robustness and shows good anti-interference capability.
Drawings
Fig. 1 is a topology structure of a photovoltaic grid-connected inverter of the present invention, wherein: u. of s Representing the network phase voltage; i represents an inverter alternating-current side phase current; l and R respectively represent the equivalent inductance and the internal resistance of the filter inductance at the AC side of the inverter; c and U dc Respectively representing the direct current side capacitance and the voltage of the inverter;
FIG. 2 is a control block diagram of a photovoltaic grid-connected inverter according to the present invention;
FIG. 3 is a voltage waveform and a phase A network access current under the control of a sliding mode;
FIG. 4 shows the voltage and current waveforms of the A-phase network under PI control;
FIG. 5 is a comparison of DC side voltages of the photovoltaic grid-connected inverter;
FIG. 6 shows the total harmonic distortion of the A-phase network access current under sliding mode control;
FIG. 7 shows the total harmonic distortion of the phase A network-connected current under PI control;
FIG. 8 is a comparison of DC side voltage with varying illumination intensity;
FIG. 9 is the inverter DC side voltage under grid voltage fluctuation;
fig. 10 shows the system frequency under grid voltage fluctuations.
Detailed Description
Example 1
A photovoltaic grid-connected inverter control method based on improved sliding mode control comprises the following steps:
step 1, in order to simplify the design of a control measuring scale, a dq rotating coordinate system is used for representing a mathematical model of a photovoltaic grid-connected inverter (shown in fig. 1):
in the formula u d ＝U dc S d ，u q ＝U dc S q ；S d 、S q D and q-axis components of the switching function, respectively; u. of sd 、u sq The components of the grid voltage on d and q axes are respectively; i.e. i d 、i q The components of the current on the alternating current side of the inverter on d and q axes are respectively; i.e. i L Is the current flowing into the inverter; l and R respectively represent the equivalent inductance and the internal resistance of the filter inductance at the AC side of the inverter; c and U dc Respectively representing the direct current side capacitance and the voltage of the inverter; ω represents angular frequency;
step 2, the design of the sliding mode controller comprises 3 parts: designing a sliding mode surface: the motion point of the system keeps good dynamic characteristics on the sliding mode surface. (2) designing an approximation law: the dynamic characteristic of the system when the moving point approaches to the sliding mode surface and the buffeting degree when the moving point approaches to the switching surface are determined. (3) designing a control rate: the control target of the sliding mode controller is met, and the system can reach the sliding mode surface from any initial state within a limited time.
In order to realize the grid-connected control target, a double closed-loop sliding mode control strategy shown in fig. 2 is adopted:
DC side voltage U of inverter dc And a reference voltage U dc * After comparison, obtaining a d-axis reference value i of the current inner ring through the voltage outer ring d * The result obtained by the current inner loop is converted by inverse Park to obtain a control signal u α 、u β 。
Considering the influence of the external uncertain disturbance on the system, equation (1) is rewritten as:
in the formula, d 1 、d 2 The item represents uncertain disturbance of power grid voltage fluctuation caused by perturbation of system parameters and load change; cd [ Cd ] 3 The term represents the uncertain disturbance of the direct current side of the inverter caused by capacitance tolerance and illumination intensity variation.
Step 2.1, the voltage outer ring selects direct-current side voltage as a controlled variable, and the voltage outer ring sliding mode controller adopts integral sliding mode control, which specifically comprises the following steps:
according to a control target of the system, selecting a direct-current side voltage as a control quantity, and defining a tracking error of a voltage outer-ring sliding mode controller as follows:
e＝U dc * -U dc (3)
the derivative of the tracking error is then:
in order to reduce the steady-state error of the system and compensate the uncertainty of the system, an integral sliding mode surface is introduced:
using an exponential approximation law, let
And (3) combining the formula (5) with the formulas (4) and (6) to obtain the sliding mode control rate of the voltage outer ring as follows:
in the formula, epsilon>|d 3 |；k>0; kS is an index approach term, and lambdae is a proportion term, and the two terms jointly ensure that the system can approach the switching surface at a higher speed when the moving point of the system is far away from the switching surface; epsilon sgn (S) is a constant-speed approach term, so that the motion point of the system can reach the switching surface in a limited time; i.e. i L and/C is a control item influenced by system parameters.
Defining a Lyapunov function
Generalized sliding mode condition is adopted for combining>
Verification of stability, i.e.
The combination of formula (2) and (7) can prove
From equation (9), it can be seen that>|d 3 |、k>Under the condition of 0, the designed voltage outer ring sliding mode controller meets the sliding mode stability condition, and meanwhile, the robustness of the system can be guaranteed.
Step 2.2, the current inner ring selects the output current of the inverter as a control quantity, and a novel approach law is introduced into the current inner ring sliding mode controller, which specifically comprises the following steps:
according to a control target of the system, the output current of the inverter is selected as a control quantity, and the tracking error of the current inner loop sliding mode controller is defined as follows:
in the formula, in order to realize unit power factor grid connection, reactive current i is required q Control is performed, i q * ＝0；
The sliding mode surface of the current inner ring sliding mode controller adopts the following steps:
in the formula, c 1 、c 2 The convergence speed of the tracking error of the current inner ring sliding mode controller is shown, and the tracking error converges an index to 0 under the sliding mode surface;
when the DC side voltage of the inverter is stabilized, consider i d * The constant is obtained by combining the vertical type (10) and the formula (11), and the obtained sliding mode surface is as follows:
combining formula (1) and formula (12):
when the system is in a steady state,
in this case, the formula (1) gives:
combining equations (13) and (14) to obtain a simplified slip form surface:
the approaching laws commonly used at present include constant velocity approaching law, exponential approaching law, power approaching law, etc. The approach speed and the buffeting degree of the constant velocity approach law depend on a single coefficient; the exponential approach law is based on the fact that an exponential term is added to improve the approach speed, but the approach speed is still larger when S is close to zero.
To reduce the chattering, it is necessary to ensure that the control gain is small as the system state approaches the sliding mode (S is small). If we further consider applying the power approximation law, the approach will be slower because there is no exponential term.
The invention adopts the following approach law:
in the formula, k 1 For constant velocity approach term coefficient, k 2 Is an exponential approximation term coefficient, k 1 、k 2 Representing the approaching speed and the buffeting degree of the system state reaching the switching surface, wherein n =1,2; alpha and beta are positive control parameters and are exponential terms of absolute values of tracking errors, and alpha and beta are constant values in a designed system. Through simulation, the value of alpha is 0.5, and the value of beta is 2.
When the system state is far away from the switching plane (| S | C |)>1) In the process, due to the existence of the control parameter beta, the second term of the approximation law is equivalent to an exponential term, and the approximation speed of the approximation law can be ensured to be higher than the power approximation law. At this time, k 2 The approach speed of the system state to the switching plane is determined.
When the system state approaches the switching plane (| S |)<1) The approximation law may ensure a smaller control gain to reduce buffeting, where k is 1 The approach speed and the buffeting degree of the system state reaching the switching surface are determined. To ensure a fast approach while attenuating buffeting, k should be increased 2 While decreasing k 1 。
The combined vertical type (1), (15) and (16) obtains the current inner ring sliding mode control rate as follows:
in the formula, constant k 12 、k 22 Is an exponential approximation term coefficient, k 11 、k 21 For constant velocity approach term coefficient, alpha 1 、α 2 、β 1 、β 2 In (0, 2)]Take the constant value inside.
k 12 、k 22 The larger the system state is, the faster the arrival speed is when the system state is far away from the switching surface; k is a radical of 11 、k 21 The larger the system state approaches the switching surface, the faster the approach speed is; but an increase in this value will also cause an increase in the degree of buffeting of the system.
In this control law, in order to reduce chattering while ensuring that the system state approaches the switching plane quickly, k should be increased 12 、k 22 While decreasing k 11 、k 21 。
Taking d-axis component of current loop sliding mode control rate as an example to perform stability analysis, and defining Lyapunov function
Then the
The binding formulae (2) and (17) can prove
As can be seen from formula (19), at k 12 >|d n |、k 22 >|d n |、k 11 >0、k 21 >Under the condition of 0, the designed current inner ring sliding mode controller meets the sliding mode stability condition, and meanwhile, the robustness of the system can be ensured.
Example 2
To verify the effectiveness of the designed sliding mode controller, a simulation model was built in MATLAB/Simulink according to fig. 2.
Under the condition of an ideal power grid, the comparison simulation research is carried out by respectively adopting double closed-loop PI control and double closed-loop sliding mode control.
The main parameters of the system are shown in table 1.
TABLE 1 System simulation parameters
1. Dynamic and steady state performance analysis
And respectively comparing the A-phase network access current and voltage waveform, the DC side voltage waveform and the total harmonic distortion rate of the network access current in the 2 control modes, and analyzing the dynamic and steady-state performances of the system response.
1.1 network entry Current and Voltage analysis
The comparison results of the a-phase network access current and the voltage waveform are shown in fig. 3 and 4, respectively. As can be seen from fig. 3 and 4, for the network-in current, the time for the PI control to reach the steady-state value is about 0.06s, and the time for the sliding mode control to reach the steady-state value is about 0.03s; in the adjusting time, the oscillation amplitude of the network access current under the PI control is obviously larger than that of the sliding mode control.
1.2 DC side Voltage analysis
The dc side voltage waveform comparison results are shown in fig. 5, and the dynamic performance comparison results are shown in table 2.
TABLE 2 comparison of dynamic behavior of DC-side voltages
As can be seen from fig. 5 and table 2, for the dc-side voltage of the inverter, under the sliding mode control, the rise time, the peak time and the adjustment time are much shorter than those of the PI control, which proves that the overall rapidity of the response of the designed sliding mode controller is better than that of the PI control; the overshoot under the sliding mode control is smaller than that of PI control, and the smoothness of the response of the designed sliding mode controller is proved to be superior to that of PI control.
1.3, total harmonic distortion analysis of network access current
The comparison results of the Total Harmonic Distortion (THD) of the a-phase network access current are shown in fig. 6 and 7. As can be seen from fig. 6 and 7, the THD under the sliding mode control is 1.81%, and the THD under the PI control is 4.13%, both of which satisfy the grid-connection standard of less than 5%, but the total harmonic distortion of the current under the sliding mode control is significantly lower than that under the PI control.
2. Robust performance analysis
2.1 Effect of illumination intensity variation on the System
In order to analyze uncertain disturbance Cd on a direct current side 3 And (4) simulating and calculating the influence on the system by taking the change of the illumination intensity as a factor of uncertain disturbance on the direct current side of the inverter.
The working environment of the photovoltaic array is as follows: the temperature is 25 ℃, and the illumination intensity is 1kW/m from 0s to 0.5s 2 At 0.5s, the flow rate was 500W/m 2 。
Fig. 8 is a comparison of dc-side voltage waveforms in the 2 control modes in this environment. As can be seen from fig. 8, during a period from 0.5s to 1s, due to abrupt change of illumination intensity, the voltage at the dc side of the inverter has different drops in the 2 control modes, and under the sliding mode control, the time for the system to recover the steady state is about 0.06s, and the maximum drop value of the voltage during the period is about 5V; the time for the system to recover the steady state under the PI control is about 0.2s, and the maximum value of the voltage drop in the period is about 10V. The sliding mode controller is designed to have stronger robustness to the disturbance of the voltage on the direct current side.
2.2 influence of grid Voltage fluctuations on the System
To analyze the uncertain disturbance d 1 、d 2 And (3) simulating the network side voltage fluctuation caused by system parameter perturbation, load change and the like by using the network voltage fluctuation to carry out simulation experiments.
The effective value of the system power grid voltage is 220V, the peak value is about 311V, and the allowable deviation is +/-10%. The grid voltage was reduced by 10% at 0.4s and returned to 311V at 0.6 s.
When the grid voltage fluctuates, the comparison results of the dc side voltage waveforms under the 2 control modes are shown in fig. 9, and the comparison results of the system frequency are shown in fig. 10.
As can be seen from fig. 9: when the voltage of the power grid is reduced for 0.4s, the voltage of the direct current side of the inverter is almost free of fluctuation under the sliding mode control; under PI control, the DC side voltage has about 2V drop, and the steady state is recovered after about 0.03 s. When the grid voltage is recovered within 0.6s, the voltage of the direct current side of the inverter under the sliding mode control is almost free from fluctuation; under PI control, the voltage of the direct current side rises by about 2V, and the voltage returns to a steady state after about 0.03 s.
As can be seen from fig. 10, when the grid voltage fluctuates, the system frequency is slightly reduced in all of the 2 control modes; the frequency reduction amplitude of the system under the sliding mode control is obviously lower than that of the PI control.
In conclusion, the designed sliding mode controller shows stronger robustness when uncertain interference occurs to the network side voltage.
Claims (5)
1. A photovoltaic grid-connected inverter control method based on improved sliding mode control is characterized by comprising the following steps:
step 1, expressing a mathematical model of the photovoltaic grid-connected inverter by using a dq rotating coordinate system:
in the formula u d ＝U dc S d ，u q ＝U dc S q ；S d 、S q D and q-axis components of the switching function, respectively; u. u sd 、u sq The components of the grid voltage on d and q axes are respectively; i.e. i d 、i q The components of the current on the alternating current side of the inverter on d and q axes are respectively; i all right angle L Is the current flowing into the inverter; l and R respectively represent equivalent inductance and internal resistance of the filter inductance at the AC side of the inverter; c and U dc Respectively representing the direct current side capacitance and the voltage of the inverter; ω represents angular frequency;
step 2, the DC side voltage U of the inverter dc And a reference voltage U dc * After comparison, obtaining a d-axis reference value i of the current inner ring through the voltage outer ring d * The result obtained by the current inner loop is subjected to inverse Park conversionObtain a control signal u α 、u β 。
2. The method for controlling the photovoltaic grid-connected inverter based on the improved sliding-mode control according to claim 1, wherein the voltage outer ring in the step 2 selects a direct-current side voltage as a control quantity, and an integral sliding-mode controller of the voltage outer ring adopts an integral sliding-mode control, specifically:
selecting direct current side voltage as a control quantity, and defining the tracking error of a voltage outer ring sliding mode controller as follows:
e＝U dc * -U dc (3)
the derivative of the tracking error is then:
introducing an integral sliding mode surface:
using an exponential approximation law, let
And (3) combining the formula (5) with the formulas (4) and (6) to obtain the sliding mode control rate of the voltage outer ring as follows:
in the formula, epsilon>|d 3 |；k>0; kS is an exponential approximation term, and lambdae is a proportion term; epsilon sgn (S) is an isokinetic approach term; i.e. i L and/C is a control item influenced by system parameters.
3. The method for controlling the photovoltaic grid-connected inverter based on the improved sliding mode control according to claim 1, wherein in the step 2, the current inner loop selects the output current of the inverter as a control quantity, and a novel approach law is introduced into the current inner loop sliding mode controller, specifically:
selecting the output current of the inverter as a control quantity, and defining the tracking error of the current inner loop sliding mode controller as follows:
in the formula i q * ＝0；
The sliding mode surface of the current inner ring sliding mode controller adopts the following steps:
in the formula, c 1 、c 2 The convergence speed of the tracking error of the current inner ring sliding mode controller is shown, and the tracking error converges an index to 0 under the sliding mode surface;
when the DC side voltage of the inverter is stabilized, consider i d * The constant is obtained by combining the vertical type (10) and the formula (11), and the obtained sliding mode surface is as follows:
combining formula (1) and formula (12):
when the system is in a steady state,
in this case, the formula (1) gives:
combining equations (13) and (14) to obtain a simplified slip form surface:
the following approach law was used:
in the formula, k 1 For constant velocity approach term coefficient, k 2 Is an exponential approximation term coefficient, k 1 、k 2 Representing the approaching speed and the buffeting degree of the system state reaching the switching surface, wherein n =1,2; alpha and beta are positive control parameters and are exponential terms of absolute values of tracking errors;
the combined vertical type (1), (15) and (16) obtains the current inner ring sliding mode control rate as follows:
in the formula, constant k 12 、k 22 Is an exponential approximation term coefficient, k 11 、k 21 For constant velocity approach term coefficient, alpha 1 、α 2 、β 1 、β 2 In (0, 2)]Take the constant value inside.
4. The method for controlling the photovoltaic grid-connected inverter based on the improved sliding-mode control according to claim 2, wherein the method for verifying the stability of the voltage outer-loop sliding-mode controller specifically comprises the following steps:
s1, considering the influence of the uncertain external interference on the system, the formula (1) is rewritten as follows:
in the formula (d) 1 、d 2 The item represents uncertain disturbance of power grid voltage fluctuation caused by system parameter perturbation and load change; cd [ Cd ] 3 The term represents uncertain disturbance of the direct current side of the inverter caused by capacitance tolerance and illumination intensity variation;
s2, defining Lyapunov function
Adopts generalized sliding mode condition>
Verification of stability, i.e.
Demonstration of the binding formulae (2), (7)
From the formula (9), in ∈>|d 3 |、k>Under the condition of 0, the voltage outer ring sliding mode controller meets the sliding mode stability condition.
5. The method for controlling the photovoltaic grid-connected inverter based on the improved sliding mode control according to claim 3, wherein the method for verifying the stability of the current inner loop sliding mode controller specifically comprises the following steps:
s1, considering the influence of the uncertain external interference on the system, the formula (1) is rewritten as follows:
in the formula, d 1 、d 2 The item represents uncertain disturbance of power grid voltage fluctuation caused by perturbation of system parameters and load change; cd [ Cd ] 3 The term represents uncertain disturbance of the direct current side of the inverter caused by capacitance tolerance and illumination intensity variation;
s2, d-axis component stability analysis of current loop sliding mode control rate:
defining a Lyapunov function
Then->
Demonstration of the combination of (2), (17)
The q-axis component stability analysis of the current loop sliding mode control rate and the d-axis component stability analysis of the current loop sliding mode control rate are in the same way;
from the formula (19), in k 12 >|d n |、k 22 >|d n |、k 11 >0、k 21 >And under the condition of 0, the current inner ring sliding mode controller meets the sliding mode stability condition.
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| CN117394407A (en) * | 2023-09-26 | 2024-01-12 | 陕西理工大学 | Active disturbance rejection control method applied to photovoltaic hybrid energy storage system |
| CN117424246A (en) * | 2023-11-13 | 2024-01-19 | 哈尔滨工业大学 | Sliding mode strategy-based photovoltaic inverter voltage-power combined control system |
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| CN117424246A (en) * | 2023-11-13 | 2024-01-19 | 哈尔滨工业大学 | Sliding mode strategy-based photovoltaic inverter voltage-power combined control system |
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