Three-phase inverter fast integration terminal sliding mode control method

Abstract

The invention discloses a three-phase inverter fast integral terminal sliding mode control method, which provides a solution for the problem of low accuracy of a traditional interference state observer, designs a super-spiral interference observer, and accurately estimates disturbance and uncertainty information of external changes and internal parameters of a three-phase inverter system by adopting a super-spiral algorithm. And secondly, a finite time observer is adopted to accurately observe the output current of the inverter system, a fast integral terminal sliding mode controller is adopted to replace a common sliding mode device, and compared with the common sliding mode controller, the fast integral terminal sliding mode controller is high in convergence speed and robustness, so that faster and more accurate control of the controller is realized. According to the control strategy, the disturbance estimation speed and accuracy of the observer can be improved, the stability error of the system is reduced, and then the transient response speed and robustness of the whole system are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a fast integral terminal sliding mode control method for a three-phase inverter. Background Art

[0002] As the most widely used and convenient new energy and power for the economic and social development, industrial and agricultural production of modern mankind, electric energy has become an important cornerstone for ensuring people's lives, scientific research and rapid social and economic development. Nowadays, modern control theory and power electronics technology are constantly improving and developing, and people's requirements for the quality and accuracy of electric energy are getting higher and higher. All sectors of society are in urgent need of finding an ideal power supply strategy for different equipment, and inverter technology has thus emerged in the public eye. It converts direct current into the required alternating current, thereby obtaining an ideal power supply that matches production applications.

[0003] As we all know, the control effect of three-phase inverters is easily affected by various multi-source interferences and uncertainties. For example, there are many forms of external interference such as electromagnetic interference and harmonic interference. These interferences have a great impact on the voltage regulation performance of the system and even affect the stability of the system. Due to the various uncertainties and external disturbances in the working conditions, the complex uncertainties have a great impact on the normal operation of the inverter. At the same time, some special application scenarios put forward higher requirements on the dynamic response and stability error of the inverter. Therefore, how to ensure the robustness of the inverter and improve the system performance indicators in the presence of multiple nonlinear interferences in the system has become a research hotspot for scholars.

[0004] As the most common control strategy in engineering, the traditional PID control method has a simple structure and is easy to implement, but its parameter setting is complex and its robustness is poor. Using the feedback linear method, a linear signal model in a small area of ​​the equilibrium point is established to achieve the closed-loop stability of the system. However, this method is relatively sensitive to interference, and the linearization method cannot effectively suppress non-matching interference. Summary of the invention

[0005] The purpose of the present invention is to provide a fast integral terminal sliding mode control method for a three-phase inverter, which can achieve fast and accurate tracking of the inverter output voltage and precise compensation and suppression of multi-source interference and uncertainty within a limited time.

[0006] The technical solution adopted by the present invention is a three-phase inverter fast integral terminal sliding mode control method, including using a state space averaging method to establish a disturbed state space average model of a three-phase full-bridge inverter; using the actual output current of the inverter and the tracking error value between the actual output current and the reference current as state variables, while considering the influence of lumped interference, establishing an error dynamic model of the inverter, and designing a super helical interference observer to obtain the desired goal of robust control design, and then designing a finite time state observer to estimate the output current; combining the output of the observer as a feedforward compensation with an output feedback control method, designing a fast integral terminal controller based on the super helical interference observer and the finite time state observer; and realizing the control of the inverter output current according to the fast integral terminal controller.

[0007] The present invention is also characterized in that:

[0008] Follow the steps below to implement it:

[0009] Step 1: Construct a mathematical model of the grid-connected three-phase inverter in the dq coordinate system;

[0010] Step 2: Convert the mathematical model established in step 1 into a spatial state model, expand the total disturbance into the spatial state model, and construct an equivalent model of the grid-connected three-phase inverter;

[0011] Step 3: Design a super-helical disturbance observer and a finite-time observer based on the equivalent model of the grid-connected three-phase inverter. The super-helical disturbance observer is used to observe the total disturbance of the system. The observed total disturbance is fed back to the finite-time observer to estimate the state variables. The second-order disturbance estimation is introduced to improve the observation accuracy of the disturbance and state variables.

[0012] Step 4: Apply the observation value obtained in step 3 to the improved fast integral terminal sliding mode controller and introduce the integral term into the sliding surface;

[0013] Step 5: According to the sliding mode controller obtained in step 4, add the bi-power reaching law;

[0014] Step 6: According to the above steps, the output of the grid-connected inverter control method based on the fast integral terminal sliding mode of the super-helical disturbance observer and the finite-time state observer is constructed, the duty cycle is obtained by SPWM modulation, and the duty cycle is applied to the control of the three-phase inverter switch tube to realize the control of the three-phase inverter.

[0015] Step 1 is as follows:

[0016] According to Kirchhoff's law, the variable relationship of the grid-connected inverter in the abc coordinate system is derived:

[0017]

[0018] In formula (1), u a 、u b 、u c is the three-phase voltage on the three-phase inverter side, i La 、i Lb 、i Lc is the three-phase current flowing through the inductor, L and C are the filter inductor and capacitor parameters respectively, R is the circuit equivalent resistance parameter, u ga 、u gb 、u gc is the AC grid voltage, i a 、i b 、i c is the three-phase current on the grid side;

[0019] The mathematical model of the inverter AC side in dq coordinates is obtained by transforming equation (1) into:

[0020]

[0021] In formula (2), ω is the grid voltage angular frequency, u d 、u q They represent the components of the inverter's AC voltage on the d and q axes, respectively. Ld 、i Lq Respectively represent the components of the inductor current on the d and q axes, i d 、i q They represent the components of the grid-side current on the d and q axes, respectively, and u dr =S d u dc ,u qr =S q u dc , S d , S q They are the d-axis and q-axis switching functions respectively. The switching function is defined as:

[0022]

[0023] Step 2 is as follows:

[0024] On the basis of the three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as follows:

[0025]

[0026] In formula (4), P ref , Q ref are the reference values ​​of active power and reactive power respectively, i dref 、i qref They are the current reference values ​​of the set active power and reactive power respectively;

[0027] The active power and reactive power in the circuit are calculated by formula (4):

[0028]

[0029] Based on this three-phase inverter, PQ control is used. PQ control includes a power outer loop and a current inner loop. The outer loop calculates the current inner loop reference value i through formula (5): dref 、i qref , and then the current inner loop control rate is designed by the differential equation (2) to control the output;

[0030] The system's internal and external disturbances and parameter perturbations are uniformly expressed as lumped disturbances, and the following disturbed model is obtained by mathematically transforming equation (2):

[0031]

[0032] In formula (6), b d 、b q are the d-axis and q-axis control gain, respectively, and f d 、f q are the equivalent lumped disturbances of d and q axes, and the lumped disturbance f d 、f q Including the unmodeled part of the system, the coupled part, and the internal and external disturbances of the system, its expression is:

[0033]

[0034] Step 3 is as follows:

[0035] Let the state variable x d1 =i d , x d3 =f d , x q1 =i q , x q3 =f q , then formula (7) can be written as follows:

[0036]

[0037] Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 x d1 、x d2 、x d3 、x q1 、x q2、x q3 According to the disturbance model of formula (6), the following finite time observer is designed:

[0038]

[0039] In formula (9), sgn(.) is the sign function, k d1 , k d2 , k q1 , k q2 is the observer gain and is a positive number; α1∈(1-ε,1), ε>0, α2=2α1;

[0040] Design the following superhelical interference observer:

[0041]

[0042] In formula (10), sgn(.) is the sign function; k 1,2,3,4 is the observer gain; Where x d,q3 The calculation is as follows:

[0043]

[0044] Step 4 is as follows:

[0045] Let the grid-side current i of d and q axes be d ,i q The deviation from the grid-side current reference value is d 、e q for:

[0046]

[0047] In formula (12), i dref for i d The reference value of i qref for i q Reference value of

[0048] dq axis traditional second-order fast terminal sliding surface s d 、s q The design is as follows:

[0049]

[0050] In formula (13), 0<λ1<1; 1<λ2<2; 0<λ3<1; 1<λ4<2; k1, k2, k3, k4, k5, k6 are positive constant gains;

[0051] The integral term is introduced into the sliding surface, so the improved fast integral terminal sliding is as follows:

[0052]

[0053] In formula (14), k7 and k8 are controller gains.

[0054] Step 5 is specifically as follows:

[0055] Derivative of formula (13) yields:

[0056]

[0057] From equation (14), we can get the equivalent control law u of the inner loop of the dq axis current: dreq 、u qreq for:

[0058]

[0059] Introduce the double power reaching law:

[0060]

[0061] In formula (17), u drsw 、u qrsw are the d-axis and q-axis switching control rates, ε1, ε2, ε4, ε5∈(0,+∞), ε3, ε6∈(0,1), and the double power reaching law is d 、s q When it approaches 0, there is s d 、s q If it is greater than 0, it means that the controller can reduce the approach speed to 0 when the system is about to reach the sliding surface, thus avoiding the switching in the conventional approaching law and eliminating the chattering of the sliding mode controller itself.

[0062] Combining equation (16) and equation (17), we can get the comprehensive control law u of dq axis: dr 、u qr for:

[0063]

[0064] The beneficial effects of the present invention are:

[0065] The fast integral terminal sliding mode control method for a three-phase inverter of the present invention proposes a solution to the problem that the accuracy of the traditional disturbance state observer is not high, designs a super-helical disturbance observer, and uses a super-helical algorithm to accurately estimate the external changes of the three-phase inverter system and the disturbance and uncertainty information of the internal parameters. Secondly, a finite time observer is used to accurately observe the output current of the inverter system, and a fast integral terminal sliding mode controller is used to replace the ordinary sliding mode controller. Compared with the ordinary sliding mode controller, the fast integral terminal sliding mode controller has a faster convergence speed and higher robustness, and realizes faster and more accurate control of the controller. This control strategy can improve the speed and accuracy of the observer's disturbance estimation, reduce the stability error of the system, and thereby improve the transient response speed and robustness of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a control block diagram of the fast integral terminal sliding mode control method of the three-phase inverter of the present invention;

[0067] Figure 2 It is the main circuit topology diagram of the three-phase grid-connected inverter;

[0068] Figure 3 It is a control block diagram of a three-phase grid-connected inverter of the present invention;

[0069] Figure 4 It is the transient waveform of the three-phase current on the grid side controlled by PI;

[0070] Figure 5 It is a transient waveform diagram of the three-phase current on the grid side controlled by the control method of the present invention;

[0071] Figure 6 This is the transient waveform of the grid-side current under PI control when the active power suddenly increases from 30kW to 75kw;

[0072] Figure 7 The transient waveform diagram of the current on the grid side controlled by the control method of the present invention when the active power suddenly increases from 30kW to 75kw;

[0073] Figure 8 This is the transient waveform of the grid-side current under PI control when the active power suddenly drops from 75kW to 30kw;

[0074] Fig. 9 The transient waveform diagram of the current on the grid side controlled by the control method of the present invention when the active power suddenly drops from 75kW to 30kw;

[0075] Fig.10 This is the harmonic analysis diagram of the grid current under PI control;

[0076] Fig.11 It is a harmonic analysis diagram of the grid current controlled by the control method of the present invention. DETAILED DESCRIPTION

[0077] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0078] Example 1

[0079] This embodiment provides a three-phase inverter fast integral terminal sliding mode control method. Figure 1 As shown, the method includes adopting the state space averaging method to establish a disturbed state space average model of the three-phase full-bridge inverter; taking the actual output current of the inverter and the tracking error value between the inverter and the reference current as state variables, considering the influence of lumped disturbance, establishing the error dynamic model of the inverter, and designing a super helical disturbance observer to obtain the desired goal of robust control design, and then designing a finite time state observer to estimate the output current; combining the output of the observer as feedforward compensation with the output feedback control method, and designing a fast integral terminal controller based on the super helical disturbance observer and the finite time state observer; according to the fast integral terminal controller, the output current of the inverter is controlled.

[0080] Example 2

[0081] This embodiment provides a three-phase inverter fast integral terminal sliding mode control method, which is implemented based on Embodiment 1 in the following steps:

[0082] Step 1: Construct a mathematical model of the grid-connected three-phase inverter in the dq coordinate system;

[0083] Three-phase grid-connected inverter circuit topology Figure 2 As shown, the DC side voltage is u in The DC voltage source is provided by controlling the inverter to output a certain power to supply the AC load. dc is the DC side voltage stabilizing capacitor, u dc is the voltage value across the DC side voltage stabilizing capacitor, i o Represents the DC side input current. According to Kirchhoff's law, the variable relationship of the grid-connected inverter in the abc coordinate system is derived:

[0084]

[0085] In formula (1), u a 、u b 、u c is the three-phase voltage on the three-phase inverter side, i La 、i Lb 、i Lc is the three-phase current flowing through the inductor, L and C are the filter inductor and capacitor parameters respectively, R is the circuit equivalent resistance parameter, u ga 、u gb 、ugc is the AC grid voltage, i a 、i b 、i c is the three-phase current on the grid side;

[0086] After coordinate transformation of equation (1), the mathematical model of the inverter AC side in dq coordinates is obtained as follows:

[0087]

[0088] In formula (2), ω is the grid voltage angular frequency, u d 、u q They represent the components of the inverter's AC voltage on the d and q axes, respectively. Ld 、i Lq Respectively represent the components of the inductor current on the d and q axes, i d 、i q They represent the components of the grid-side current on the d and q axes, respectively, and u dr =S d u dc ,u qr =S q u dc , S d , S q They are the d-axis and q-axis switching functions respectively. The switching function is defined as:

[0089]

[0090] Step 2: Convert the mathematical model established in step 1 into a spatial state model, expand the total disturbance into the spatial state model, and construct an equivalent model of the grid-connected three-phase inverter;

[0091] On the basis of the three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as follows:

[0092]

[0093] In formula (4), P ref , Q ref are the reference values ​​of active power and reactive power respectively, i dref 、i qref They are the current reference values ​​of the set active power and reactive power respectively;

[0094] The active power and reactive power in the circuit are calculated by formula (4):

[0095]

[0096] Based on this three-phase inverter, PQ control is used. PQ control includes a power outer loop and a current inner loop. The outer loop calculates the current inner loop reference value i through formula (5): dref 、i qref , and then the current inner loop control rate is designed by the differential equation (2) to control the output;

[0097] The system's internal and external disturbances and parameter perturbations are uniformly expressed as lumped disturbances, and the following disturbed model is obtained by mathematically transforming equation (2):

[0098]

[0099] In formula (6), b d 、b q are the d-axis and q-axis control gain, respectively, and f d 、f q are the equivalent lumped disturbances of d and q axes, and the lumped disturbance f d 、f q Including the unmodeled part of the system, the coupled part, and the internal and external disturbances of the system, its expression is:

[0100]

[0101] Step 3: Design a super-helical disturbance observer and a finite-time observer based on the equivalent model of the grid-connected three-phase inverter. The super-helical disturbance observer is used to observe the total disturbance of the system. The observed total disturbance is fed back to the finite-time observer to estimate the state variables. The second-order disturbance estimation is introduced to improve the observation accuracy of the disturbance and state variables.

[0102] Step 4: Apply the observation value obtained in step 3 to the improved fast integral terminal sliding mode controller and introduce the integral term into the sliding surface;

[0103] Step 5: According to the sliding mode controller obtained in step 4, add the bi-power reaching law;

[0104] Step 6: According to the above steps, the output of the grid-connected inverter control method based on the fast integral terminal sliding mode of the super-helical disturbance observer and the finite-time state observer is constructed, the duty cycle is obtained by SPWM modulation, and the duty cycle is applied to the control of the three-phase inverter switch tube to realize the control of the three-phase inverter.

[0105] Example 3

[0106] This embodiment provides a three-phase inverter fast integral terminal sliding mode control method. Based on the embodiment 1-2, step 3 is specifically as follows:

[0107] Let the state variable x d1 =i d , xd3 =f d , x q1 =i q , x q3 =f q , then formula (7) can be written as follows:

[0108]

[0109] Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 x d1 、x d2 、x d3 、x q1 、x q2 、x q3 According to the disturbance model of formula (6), the following finite time observer is designed:

[0110]

[0111] To avoid chattering, a gain similar to that in equation (9) is selected, where sgn(.) is the sign function and k d1 , k d2 , k q1 , k q2 is the observer gain and is a positive number; α1∈(1-ε,1), ε>0, α2=2α1;

[0112] Design the following superhelical interference observer:

[0113]

[0114] In formula (10), sgn(.) is the sign function; k 1,2,3,4 is the observer gain; Where x d,q3 The calculation is as follows:

[0115]

[0116] Step 4 is as follows:

[0117] Let the grid-side current i of d and q axes be d ,i q The deviation from the grid-side current reference value is d 、e q for:

[0118]

[0119] In formula (12), i dref for i d The reference value of i qref for i q Reference value of

[0120] dq axis traditional second-order fast terminal sliding surface s d 、s q The design is as follows:

[0121]

[0122] In formula (13), 0<λ1<1; 1<λ2<2; 0<λ3<1; 1<λ4<2; k1, k2, k3, k4, k5, k6 are positive constant gains; when the sliding mode is in the arrival stage, Plays a major role when the sliding mode is in a stable stage. Plays a major role. The size of k1, k2, k4, and k5 determines the weight of the sliding surface in the two stages. Usually, k2 and k5 are larger to improve the rapidity of system stability. k3 and k6 are used to ensure that the change trend of e1 tends to zero.

[0123] Compared with the linear sliding surface, the integral sliding surface introduces an integral term in the sliding surface to improve the robustness of the system and the tracking accuracy of the system. Therefore, the improved fast integral terminal sliding is as follows:

[0124]

[0125] In formula (14), k7 and k8 are controller gains.

[0126] Example 4

[0127] This embodiment provides a three-phase inverter fast integral terminal sliding mode control method. Based on embodiments 1-3, step 5 is specifically as follows:

[0128] Derivative of formula (13) yields:

[0129]

[0130] From equation (14), we can get the equivalent control law u of the inner loop of the dq axis current: dreq 、u qreq for:

[0131]

[0132] Introduce the double power reaching law:

[0133]

[0134] In formula (17), udrsw 、u qrsw are the d-axis and q-axis switching control rates, ε1, ε2, ε4, ε5∈(0,+∞), ε3, ε6∈(0,1), and the double power reaching law is d 、s q When it approaches 0, there is s d 、s q If it is greater than 0, it means that the controller can reduce the approach speed to 0 when the system is about to reach the sliding surface, thus avoiding the switching in the conventional approaching law and eliminating the chattering of the sliding mode controller itself.

[0135] Combining equation (16) and equation (17), we can get the comprehensive control law u of dq axis: dr 、u qr for:

[0136]

[0137] The present invention controls the three-phase grid-connected inverter as follows: Figure 3 shown.

[0138] From the above content, it can be seen that the fast integral terminal sliding mode control method of the three-phase inverter of the present invention has the following advantages:

[0139] 1) The superhelical disturbance observer and fixed time observer used in the present invention can estimate low-frequency and high-frequency disturbances without establishing an accurate mathematical model of the inverter system, and the first-order derivative of the disturbance of the observed object does not need to be zero, which is particularly suitable for inverters with large internal parameter changes and uncertain information such as external changes. The observer uses the superhelical algorithm to improve the accuracy and speed of the observer's observation of external and internal parameter disturbances.

[0140] 2) The fast integral terminal sliding mode controller adopted in the present invention obtains the current in the two-phase rotating coordinate system by transforming the three-phase output current through the dq coordinate system, and obtains the current tracking error as input, and then introduces the integral term to correct the system layer by layer, so that the system has higher accuracy and robustness, and ensures the global stability of the system when subjected to internal and external disturbances.

[0141] 3) The superhelical function adopted by the present invention has a fast and stable convergence speed, so that the interference error converges to zero in a limited time, thereby achieving the expected performance. It consists of two parts. First, a continuous function of the error variable can be obtained, so that the error signal also appears to be a continuous state; second, the integral of the discontinuous time derivative exists in the error, which avoids the occurrence of chattering.

[0142] Simulation Analysis

[0143] In order to verify the feasibility of the fast integral terminal sliding mode control method of the three-phase inverter of the present invention, in the grid-connected inverter model built in the Matlab / Simulink platform, under the control method of the present invention and the traditional PI control, when the active power suddenly changes, the output of the stable operation 30kW suddenly increases to 75kW at 0.2s, and the corresponding three-phase current amplitude suddenly increases from 45.5A to 114.2A; at 0.3s, it suddenly drops from 75kW to 30kW, and the corresponding three-phase current amplitude suddenly drops from 114.2A to 45.5A, resulting in the dynamic response of the three-phase current output on the AC side of the three-phase inverter. Figure 4 As shown in the figure, under the traditional PI control, the response time of the three-phase current on the grid side is 23.1ms at 0.2s, and the response time of the three-phase current on the grid side is 29.9ms at 0.3s. Figure 5 As shown, under the control of the present invention, the response time of the three-phase current on the grid side is 13.4ms at 0.2s, and the response time of the three-phase current on the grid side is 13.1ms at 0.3s. By comparison, it can be seen that the control method of the present invention greatly reduces the transient time and improves the stability of the system.

[0144] In order to verify the effectiveness of the control method designed in the present invention, a simulation circuit is built in a hardware-in-the-loop (HIL) experimental platform, and a comparative analysis is performed with the traditional PI control strategy. It is defined that the power is positive when the voltage and current directions are consistent. The simulation parameter settings are shown in Table 1.

[0145] Table 1 Circuit parameters

[0146] parameter Numeric Grid voltage amplitude e 311V Filter inductor L 5mH Filter capacitor C 50μF Inductor parasitic resistance R 0.01Ω <![CDATA[DC regulated capacitor C dc > 2.2mF <![CDATA[Battery terminal voltage v bat > 800V Load power 20kW-70kW

[0147] The present invention proposes a solution to the problem that the traditional disturbance state observer has low accuracy, designs a super-helical disturbance observer, and uses a super-helical algorithm to accurately estimate the external changes of the three-phase inverter system and the disturbance and uncertainty information of the internal parameters. A finite-time observer is used to accurately observe the output current of the inverter system, and a fast integral terminal sliding mode controller is used to replace the ordinary sliding mode controller. Compared with the ordinary sliding mode controller, the fast integral terminal sliding mode controller has a fast convergence speed and high robustness, and realizes faster and more accurate control of the controller. This control strategy can improve the speed and accuracy of the observer's disturbance estimation, reduce the stability error of the system, and thus improve the transient response speed and robustness of the entire system.

[0148] Depend on Figure 6 It can be seen that when the inverter output active power suddenly increases from 30kW to 75kw, i dThe jump from 53A to 152A. The transition time from 30kW to 75kW under the PI control strategy is 18.5ms. The jump caused by the sudden increase in power produces a certain amount of overshoot. In addition, due to the coupling between powers, the transient process of reactive power is also caused when the active power changes suddenly, such as Figure 6 The framed part. Figure 7 It can be seen that under the control method of the present invention, when the inverter output active power suddenly increases from 30kW to 75kw, the transition time of the jump caused by the sudden power increase is 10.3ms, and the fluctuation of the current value during steady-state operation is smaller than that of PI control.

[0149] Depend on Figure 8 It can be seen that when the inverter output active power jumps from 75kW to 30kW, i d The jump from 152A to 53A. The transition time from 75kW to 30kW under the PI control strategy is 18.5ms. The jump caused by the sudden power reduction produces a certain amount of overshoot. In addition, due to the coupling between the powers, the transient process of reactive power is also caused when the active power changes suddenly, such as Figure 8 Framed part. Fig. 9 It can be seen that under the control method of the present invention, when the inverter output active power suddenly drops from 75kW to 30kw, the transition time of the jump caused by the sudden power reduction is 9.7ms, and the fluctuation of the current value during steady-state operation is smaller than that of PI control.

[0150] In order to verify the influence of the control method of the present invention on the power quality of the inverter output current, the grid-connected current of the inverter output active power of 30kW was subjected to Fourier analysis of two steady-state cycles in Matlab / Simulink software. Fig.10 As shown, it is the harmonic analysis of the grid-connected current of the energy storage converter under the traditional PI control, and the THD is 4.12%. Fig.11 The figure shows the harmonic analysis of the grid-connected current of the energy storage converter under the control of the present invention, and the THD is 1.37%. By comparison, it can be seen that the control of the present invention has a stronger harmonic suppression capability and improves the quality of grid-connected power.

[0151] In summary, the fast integral terminal sliding mode control method of the three-phase inverter of the present invention effectively solves the coupling influence of the external disturbance and the current inner loop on the three-phase grid-connected inverter in the working mode, improves the control accuracy and convergence speed of the inverter when receiving interference. The present invention has good robustness and can effectively improve the power quality of the power grid.

Claims

1. A fast integral terminal sliding mode control method for a three-phase inverter, characterized in that: It includes using the state space averaging method to establish a disturbed state space average model of the three-phase full-bridge inverter; taking the actual output current of the inverter and the tracking error value between the reference current as the state variables, while considering the influence of the lumped disturbance, establishing the error dynamic model of the inverter, and designing a superhelical disturbance observer to obtain the desired goal of the robust control design, and then designing a finite time state observer to estimate the output current; combining the output of the observer as a feedforward compensation with the output feedback control method, and designing a fast integral terminal controller based on the superhelical disturbance observer and the finite time state observer; based on the fast integral terminal controller, the output current of the inverter is controlled.

2. The three-phase inverter fast integral terminal sliding mode control method according to claim 1, characterized in that: Follow the steps below to implement it: Step 1: Construct a mathematical model of the grid-connected three-phase inverter in the dq coordinate system; Step 2: Convert the mathematical model established in step 1 into a spatial state model, expand the total disturbance into the spatial state model, and construct an equivalent model of the grid-connected three-phase inverter; Step 3: Design a super-helical disturbance observer and a finite-time observer based on the equivalent model of the grid-connected three-phase inverter. The super-helical disturbance observer is used to observe the total disturbance of the system. The observed total disturbance is fed back to the finite-time observer to estimate the state variables. The second-order disturbance estimation is introduced to improve the observation accuracy of the disturbance and state variables. Step 4: Apply the observation value obtained in step 3 to the improved fast integral terminal sliding mode controller and introduce the integral term into the sliding surface; Step 5: According to the sliding mode controller obtained in step 4, add the bi-power reaching law; Step 6: According to the above steps, the output of the grid-connected inverter control method based on the fast integral terminal sliding mode of the super-helical disturbance observer and the finite-time state observer is constructed, the duty cycle is obtained by SPWM modulation, and the duty cycle is applied to the control of the three-phase inverter switch tube to realize the control of the three-phase inverter.

3. The three-phase inverter fast integral terminal sliding mode control method according to claim 2, characterized in that: The step 1 specifically comprises: According to Kirchhoff's law, the variable relationship of the grid-connected inverter in the abc coordinate system is derived: In formula (1), u a 、u b 、u c is the three-phase voltage on the three-phase inverter side, i La 、i Lb 、i Lc is the three-phase current flowing through the inductor, L and C are the filter inductor and capacitor parameters respectively, R is the circuit equivalent resistance parameter, u ga 、u gb 、u gc is the AC grid voltage, i a 、i b 、i c is the three-phase current on the grid side; The mathematical model of the inverter AC side in dq coordinates is obtained by transforming equation (1) into: In formula (2), ω is the grid voltage angular frequency, u d 、u q They represent the components of the inverter's AC voltage on the d and q axes, respectively. Ld 、i Lq Respectively represent the components of the inductor current on the d and q axes, i d 、i q They represent the components of the grid-side current on the d and q axes, respectively, and u dr =S d u dc ,u qr =S q u dc , S d , S q They are the d-axis and q-axis switching functions respectively. The switching function is defined as:

4. The three-phase inverter fast integral terminal sliding mode control method according to claim 3, characterized in that: The step 2 is specifically as follows: On the basis of the three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as follows: In formula (4), P ref , Q ref are the reference values ​​of active power and reactive power respectively, i dref 、i qref They are the current reference values ​​of the set active power and reactive power respectively; The active power and reactive power in the circuit are calculated by formula (4): Based on this three-phase inverter, PQ control is used. PQ control includes a power outer loop and a current inner loop. The outer loop calculates the current inner loop reference value i through formula (5): dref 、i qref , and then the current inner loop control rate is designed by the differential equation (2) to control the output; The system's internal and external disturbances and parameter perturbations are uniformly expressed as lumped disturbances, and the following disturbed model is obtained by mathematically transforming equation (2): In formula (6), b d , b q are the d-axis and q-axis control gain, respectively, and f d 、f q are the equivalent lumped disturbances of d and q axes, and the lumped disturbance f d 、f q Including the unmodeled part of the system, the coupled part, and the internal and external disturbances of the system, its expression is:

5. The three-phase inverter fast integral terminal sliding mode control method according to claim 4, characterized in that: The step 3 is specifically as follows: Let the state variable x d1 =i d , x d3 =f d , x q1 =i q , x q3 =f q , then formula (7) can be written as follows: Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 x d1 、x d2 、x d3 、x q1 、x q2 、x q3 According to the disturbance model of formula (6), the following finite time observer is designed: In formula (9), sgn(.) is the sign function, k d1 , k d2 , k q1 , k q2 is the observer gain and is a positive number; α1∈(1-ε,1), ε>0, α2=2α1; Design the following superhelical interference observer: In formula (10), sgn(.) is the sign function; k 1,2,3,4 is the observer gain; Where x d,q3 The calculation is as follows:

6. The three-phase inverter fast integral terminal sliding mode control method according to claim 5, characterized in that: The step 4 is specifically as follows: Let the grid-side current i of d and q axes be d ,i q The deviation between the grid-side current reference value and d 、e q for: In formula (12), i dref for i d The reference value of i qref for i q Reference value of dq axis traditional second-order fast terminal sliding surface s d 、s q The design is as follows: In formula (13), 0<λ1<1; 1<λ2<2; 0<λ3<1; 1<λ4<2; k1, k2, k3, k4, k5, k6 are positive constant gains; The integral term is introduced into the sliding surface, so the improved fast integral terminal sliding is as follows: In formula (14), k7 and k8 are controller gains.

7. The three-phase inverter fast integral terminal sliding mode control method according to claim 6, characterized in that: The step 5 is specifically as follows: Derivative of formula (13) yields: From equation (14), we can get the equivalent control law u of the inner loop of the dq axis current: dreq 、u qreq for: Introduce the double power reaching law: In formula (17), u drsw 、u qrsw are the d-axis and q-axis switching control rates, ε1, ε2, ε4, ε5∈(0,+∞), ε3, ε6∈(0,1), and the double power reaching law is d 、s q When it approaches 0, there is s d 、s q If it is greater than 0, it means that the controller can reduce the approach speed to 0 when the system is about to reach the sliding surface, thus avoiding the switching in the conventional approaching law and eliminating the chattering of the sliding mode controller itself. Combining equation (16) and equation (17), we can get the comprehensive control law u of dq axis: dr 、u qr for:

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