Improved sliding-mode active-disturbance-rejection control method for two-stage energy storage converter

Abstract

The invention discloses an improved sliding-mode active-disturbance-rejection control method for a two-stage energy storage converter, and the method comprises the steps: firstly, building a mathematical model of the energy storage converter in a three-phase static coordinate system, converting the mathematical model into a d-q rotating coordinate system, converting the mathematical model into a second-order active-disturbance-rejection normal form on the basis, and then carrying out the design of a super-spiral expansion state observer. In order to reduce system buffeting, a discontinuous switching item sign function in the super-spiral expansion state observer is replaced by a hyperbola function; secondly, a variable gain function which can change in real time along with observation errors is designed to replace the linear gain of ST-ESO, so that the disturbance observation capability is improved; and then, a superhelix integral terminal sliding mode is introduced as a feedback controller, so that the control precision and the convergence speed of the system are improved, and the robustness of the system is better improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to an improved sliding mode anti-disturbance control method for a two-stage energy storage converter. Background Art

[0002] As the core pillar of the future energy system, renewable energy is developing at an unprecedented speed. However, the intermittent and volatile nature of renewable energy poses a challenge to the stability of the power grid, and energy storage technology has become the key to solving this problem. As a bridge connecting the energy storage system and the power grid, the control performance of the energy storage inverter directly affects the efficiency and stability of the energy storage system.

[0003] The main function of the energy storage inverter is to achieve bidirectional conversion of electric energy, that is, it can convert the AC power in the power grid into DC power to charge the energy storage battery, and it can also convert the DC power in the energy storage battery into AC power to supply the power grid. Through precise control strategies, the energy storage inverter can achieve accurate management of the charging and discharging process of the energy storage battery, thereby ensuring the efficient operation of the energy storage system. With the large-scale access of renewable energy, the volatility and uncertainty of the power grid have increased, which has put forward higher requirements on the response speed and stability of the energy storage inverter. Summary of the invention

[0004] The purpose of the present invention is to provide an improved sliding mode anti-disturbance control method for a two-stage energy storage converter, which can better suppress output current fluctuations when a power mutation occurs in the energy storage converter.

[0005] The technical solution adopted by the present invention is to improve the sliding mode anti-disturbance control method of a two-stage energy storage converter. First, a mathematical model of the energy storage converter in a three-phase stationary coordinate system is established and converted to a dq rotating coordinate system. The inner loop coupling terms and unmodeled parts of the current of the d and q axes and the internal and external interferences of the inner loop are regarded as the total disturbance of the inner loop, and are expanded into new state variables. On this basis, they are converted into a second-order anti-disturbance paradigm form, and then a super-helical expanded state observer is designed. The sign function of the discontinuous switching term in the super-helical expanded state observer is replaced by a hyperbolic function; a variable gain function that changes in real time with the observation error is designed to replace the linear gain of the ST-ESO; and a super-helical integral terminal sliding mode is introduced as a feedback controller.

[0006] The present invention is also characterized in that:

[0007] Follow the steps below to implement it:

[0008] Step 1: Establish a mathematical model of the two-stage energy storage converter in the dq rotating coordinate system and convert it into a second-order active disturbance rejection paradigm;

[0009] Step 2: Controller design;

[0010] Step 2.1: Design of power outer loop controller;

[0011] Step 2.2: Design of current inner loop controller;

[0012] Step 2.2.1: Design of variable gain superhelical ESO;

[0013] Step 2.2.2: Design of super-helical integral terminal sliding mode controller.

[0014] Step 3: Obtain the control output through the controller, use SPWM modulation to obtain the duty cycle, and apply the duty cycle to the control of the energy storage converter switch tube, thereby realizing the signal control of the energy storage converter.

[0015] The present invention is also characterized in that:

[0016] Step 1 is specifically as follows:

[0017] During the grid-connected operation of the energy storage converter, the working states of the two switches in each bridge arm are complementary. Therefore, the switching function is defined as follows:

[0018]

[0019] In formula (1), j = a, b, c, representing the three phases a, b, and c of the AC power grid;

[0020] According to Kirchhoff's law, the voltage and current relationship equation of the energy storage converter in the abc three-phase stationary coordinate system is:

[0021]

[0022] In formula (2), u a 、u b 、u c is the three-phase voltage on the AC side of the two-stage energy storage converter; i sa 、i sb 、i sc is the three-phase current on the AC side; e a 、e b 、e c is the AC grid voltage; L is the filter inductance; C dc is the DC side capacitance parameter; R is the line equivalent resistance parameter; i r is the output current of the DC side converter; u dc 、i C is the DC bus voltage and current; s ka 、s kb 、s kc They are the switch control signals of the three-phase bridge arms a, b and c respectively;

[0023] Performing Park transformation on equation (2), we can obtain the mathematical model of the converter in the dq coordinate system:

[0024]

[0025] In formula (3), ω is the angular frequency of the grid voltage; e d 、i d 、s d They are the grid voltage, current, and switching function of the d-axis, and the e-axis q 、i q 、s q are the grid voltage, current and switch function of the q axis respectively; L is the filter inductance; u dc 、i C is the DC bus voltage and current.

[0026] Step 2.1 is as follows:

[0027] According to the instantaneous power theory, in order to make the energy storage converter close to unity power factor and connected to the grid, the reactive current is always equal to 0. Under the condition of balanced voltage of the three-phase grid, the instantaneous values ​​of active power P and reactive power Q on the grid side of the energy storage converter are expressed as:

[0028]

[0029] From formula (4), we know that through i d and i q Control P and Q separately to achieve independent regulation of active power and reactive power; transform equation (4) to ref , Q ref When given, the d and q axis current reference values ​​are directly obtained by calculation; however, in order to eliminate the steady-state error, the PI regulator is introduced. After the deviation between P, Q and the P, Q command values ​​is adjusted by PI, the active current reference value i is obtained based on the instantaneous power theory and the dynamic response of the system P and Q. dref and reactive current reference value i qref , as shown below:

[0030]

[0031] In formula (5), P ref , Q ref For given active power and reactive power reference values, i dref 、i qref is the inner loop reference value of d and q axis current, k dp , k di is the d-axis PI adjustment parameter, k qp , k qi is the q-axis PI adjustment parameter.

[0032] Step 2.2.1 is as follows:

[0033] First, define the state variable d and the q-axis current i d 、i q x d1 、x q1 , from formula (3):

[0034]

[0035] The inner loop coupling terms and unmodeled parts of the current in the d and q axes as well as the internal and external disturbances of the inner loop are regarded as the total disturbance of the inner loop, and are expressed as f d1 、f q1 It means that the derivative of formula (3) is converted into the ADRC paradigm as follows:

[0036]

[0037] In formula (7), b d 、b q are the gains of the d-axis and q-axis control quantities respectively;

[0038] Definition b do 、b qo is the estimated value of the d and q axis control gain, let Transform formula (7) into the following form:

[0039]

[0040] In formula (8), f d =(b d -b do )s d +f d1 , f q =(b q -b qo )s q +f q1 , b do 、b qo is the estimated value of the d and q axis control quantity gain;

[0041] f d 、f q Expand to new state variables z d3 、z q3 , the superhelical expansion state observer is designed as follows:

[0042]

[0043] In formula (9), z d1 For x d1 The estimated value of z q1For x q1 The estimated value of z d2 , z q2 is the estimated value of the derivative, x d1 For x q1 The estimated value of the derivative; e d1 is the difference between the observed value and the actual value of the d-axis, e q1 is the difference between the observed value and the actual value of the q axis; z d3 is the total disturbance f including d-axis coupling, internal disturbance and unmodeled part. d The estimated value of z q3 is the total disturbance f including the q-axis coupling term, internal disturbance and unmodeled part. q The estimated value of β d1 , β d2 , β d3 , β q1 , β q2 , β q3 is the observer gain. When the observation error e of the superhelical ESO is close to 0, the expression of the observer is consistent with that of the linear extended state observer. Therefore, the bandwidth method is used for tuning as follows:

[0044] The value conditions of β1, β2, β3 are: β1 = 3ω0, β2 = 3ω0 2 , β3=ω0 3 ;

[0045] In order to reduce system chattering and improve the observation capability of the superhelical extended state observer to the total disturbance of the inner loop, a variable gain superhelical ESO is proposed, and the sign function of the discontinuous switching term in the superhelical extended state observer is replaced by a hyperbolic function; secondly, a variable gain function that changes in real time with the observation error is designed to replace the linear gain of the ST-ESO, so as to improve the observation capability of the disturbance;

[0046] The switching function sign expression is:

[0047]

[0048] It can be seen from formula (10) that the sign function is a discontinuous function. When the sign function sign is used as the switching function of the super-helical sliding mode expansion state observer, discontinuous switching control characteristics will be generated along with the observation error, resulting in chattering problems and affecting the observation accuracy of the system. Therefore, a smooth hyperbolic function F(e i ) as the switching function of the observer;

[0049] Hyperbolic F(e i ) function is expressed as:

[0050]

[0051] The improved supercoil ESO expression is:

[0052]

[0053] In formula (12), z d1 For x d1 The improved estimate of the observer, z q1 For x q1 The improved estimate of the observer; d2 For x d1 The observer-improved estimate of the derivative, z q2 For x q1 The observer-improved estimate of the derivative; z d3 is the total disturbance f including coupling terms, internal disturbances and unmodeled parts. d The improved estimate of the observer, z q3 is the total disturbance f including coupling terms, internal disturbances and unmodeled parts. q The improved estimate of the observer; The improved variable gain function of the observer is as follows:

[0054]

[0055] The expression of variable gain L(t) is:

[0056]

[0057] In formula (14), η i , σ are both adjustable positive real numbers, and σ determines the observation accuracy of the improved superhelical ESO.

[0058] Step 2.2.2 is as follows:

[0059] Define the system state error d, the deviation between the actual current and the reference current of the q axis is e d 、e q :

[0060]

[0061] According to the current deviation e in formula (15), the integral terminal sliding surface S is designed as follows:

[0062]

[0063] In formula (16), α, β, λ, η are all positive numbers, 0<γ<1, p, q are positive odd numbers, and

[0064] Derivative the sliding surface S of formula (16) and substitute formula (8) into it, we can get:

[0065]

[0066] According to the equivalent control theory, The equivalent control law of the system is as follows:

[0067]

[0068] In order to weaken chattering and accelerate the system state to reach the sliding mode surface, the superhelical reaching law is introduced as the sliding mode switching control part. The superhelical control law consists of two parts, which are designed as follows:

[0069]

[0070] In formula (19), l1 and l2 are both constants greater than 0;

[0071] Combining equations (18) and (19) we can get the overall control law s of the system, which is expressed as follows:

[0072] s=s eq +s sw (20)

[0073] Substituting the observed values ​​of the d-axis and q-axis variables of the ESO in equation (12), we can obtain the final control law of the converter: d 、s q for

[0074]

[0075] The beneficial effects of the present invention are:

[0076] The present invention is an improved sliding mode auto-disturbance rejection control method for a two-stage energy storage converter. First, the PCS is modeled and converted into a second-order auto-disturbance rejection paradigm, and on this basis, the observer and controller are designed. The specific effects are as follows:

[0077] 1) In the improved sliding mode anti-disturbance control method for the two-stage energy storage converter of the present invention, the sign function is a discontinuous function. When it is used as the switching function of the super-helical sliding mode extended state observer, a discontinuous switch control characteristic caused by the observation error will appear. This characteristic is often accompanied by a chattering problem, which will interfere with the observation accuracy of the system. Therefore, the smooth hyperbolic function F(e i ), which is used as the switching function of the observer to reduce system chattering and keep the system stable;

[0078] 2) A variable gain function that can change in real time with the observation accuracy is designed to replace the fixed value gain of ST-ESO, so as to improve the observer's ability to observe disturbances and improve the convergence speed of the system;

[0079] 3) The superhelical integral terminal sliding mode of the present invention adopts the concept of superhelical control, and changes the sliding mode of the traditional sliding mode control to the superhelical motion mode, so that the system state can be adjusted more efficiently and stably. This control method will not cause abnormal fluctuations and instability in the system state when dynamically switching the control mode, ensuring the stable operation of the system. At the same time, the superhelical integral terminal sliding mode control can achieve high-precision control of the system state;

[0080] 4) In traditional sliding mode control, due to the presence of high-frequency switching, the system may produce chattering. However, the sensitized super-helical integral terminal sliding modes of the present invention use integrals to obtain the actual control quantity, which does not contain high-frequency switching. Therefore, there is no chattering in the system, which improves the stability and reliability of the system. At the same time, the super-helical integral terminal sliding mode control has extremely strong robustness, can effectively overcome the uncertainty of the system, and has strong resistance to interference and unmodeled dynamics. This allows the system to maintain good control performance when facing external interference or parameter changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 It is a control block diagram of an improved sliding mode anti-disturbance control method for a two-stage energy storage converter of the present invention;

[0082] Figure 2 It is a structural diagram of a two-stage energy storage converter;

[0083] Figure 3 is the hyperbolic function F(e i ) and sign(x) comparison chart;

[0084] Figure 4 It is a control diagram of an improved sliding mode anti-disturbance control method for a two-stage energy storage converter of the present invention;

[0085] Figure 5 is the DC bus voltage response diagram under different controls;

[0086] Figure 6 This is the bus voltage transient response diagram when P jumps from 30kW to 80kW under PI control;

[0087] Figure 7 This is the bus voltage transient response diagram when P jumps from 80kW to 30kW under PI control;

[0088] Figure 8 This is a bus voltage transient response diagram when P jumps from 30kW to 80kW under the control method of the present invention;

[0089] Fig. 9 This is a bus voltage transient response diagram when P jumps from 80kW to 30kW under the control method of the present invention;

[0090] Fig.10 This is the transient response diagram when the active power direction switches from 30kW to -30kW under PI control;

[0091] Fig.11 This is the transient response diagram when the active power direction switches from -30kW to 30kW under PI control;

[0092] Fig.12 It is a transient response diagram when the active power direction is switched when P jumps from 30kW to -30kW under the control method of the present invention;

[0093] Fig.13 It is a transient response diagram when the active power direction is switched when P jumps from -30kW to 30kW under the control method of the present invention;

[0094] Fig.14 This is the current harmonic analysis diagram under PI control;

[0095] Fig.15 This is a current harmonic analysis diagram when the control method of the present invention is used for control. DETAILED DESCRIPTION

[0096] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0097] Example 1

[0098] This embodiment provides an improved sliding mode anti-disturbance control method for a two-stage energy storage converter. Figure 1 As shown in the figure, firstly, the mathematical model of the energy storage converter in the three-phase stationary coordinate system is established and converted to the dq rotating coordinate system. On this basis, it is converted into the second-order anti-disturbance paradigm, and then the super-helical extended state observer is designed. In order to reduce the system chattering, the discontinuous switching term sign function in the super-helical extended state observer is replaced by a hyperbolic function; secondly, a variable gain function that can change in real time with the observation error is designed to replace the linear gain of the ST-ESO, so as to improve the observation ability of the disturbance. Then the super-helical integral terminal sliding mode is introduced as a feedback controller to improve the system control accuracy and convergence speed, and better improve the robustness of the system.

[0099] Follow the steps below to implement it:

[0100] Step 1: Establish a mathematical model of the two-stage energy storage converter in the dq rotating coordinate system and convert it into a second-order active disturbance rejection paradigm;

[0101] The two-stage energy storage converter mainly involves energy conversion and control to ensure that it can operate stably and efficiently in different working modes. Its circuit topology is as follows: Figure 2As shown, when the battery pack works in the discharge mode, the energy stored inside it is first boosted to the preset DC bus voltage by the front-stage DC / DC converter; then, the boosted DC power is inverted into AC power by the rear-stage DC / AC module, which can be fed back to the power grid or supplied to the load. In the charging mode, the AC power of the power grid is first rectified by the rear-stage DC / AC module and converted into DC power; then, the DC power enters the front-stage DC / DC module, and the DC / DC module steps down its voltage to a level suitable for charging the battery pack, and then passes it to the battery pack for charging; the converter part adopts PQ control (constant power control), which is an important control strategy in the power system, mainly used to maintain the stability and reliability of the power system. Its core principle is to ensure that the output power reaches the preset value by controlling the current, thereby realizing precise control of the active power and reactive power in the power system;

[0102] Figure 2 in, u in is the DC side power supply voltage of the converter; s1~s6 are the six switch tubes on the converter bridge arm; i o is the converter input current; it is assumed that the three-phase waveform of the grid voltage is symmetrical and has no distortion;

[0103] During the grid-connected operation of the energy storage converter, the working states of the two switches in each bridge arm are complementary. Therefore, the switching function is defined as follows:

[0104]

[0105] In formula (1), j = a, b, c, representing the three phases a, b, c of the AC power grid;

[0106] Depend on Figure 2 According to Kirchhoff's law, the voltage and current relationship equation of the energy storage converter in the abc three-phase stationary coordinate system is:

[0107]

[0108] In formula (2), u a 、u b 、u c is the three-phase voltage on the AC side of the two-stage energy storage converter; i sa 、i sb 、i sc is the three-phase current on the AC side; e a 、e b 、e c is the AC grid voltage; L is the filter inductance; C dc is the DC side capacitance parameter; R is the line equivalent resistance parameter; i r is the output current of the DC side converter; u dc、i C is the DC bus voltage and current; s ka 、s kb 、s kc They are the switch control signals of the three-phase bridge arms a, b and c respectively;

[0109] Performing Park transformation on equation (2), we can obtain the mathematical model of the converter in the dq coordinate system:

[0110]

[0111] In formula (3), ω is the angular frequency of the grid voltage; e d 、i d 、s d They are the grid voltage, current, and switching function of the d-axis, and the e-axis q 、i q 、s q are the grid voltage, current and switch function of the q axis respectively; L is the filter inductance; u dc 、i C is the DC bus voltage and current.

[0112] Step 2: Controller design;

[0113] The present invention adopts a PQ control strategy for converter control. PQ control usually involves two key control loops: a power outer loop and a current inner loop. The outer loop determines the active power and reactive power that the converter should provide according to the system operation requirements, and calculates the corresponding dq axis current reference value i according to the set P and Q values. dref 、i qref ; The current inner loop monitors the current component i at the output of the converter in real time d and i q , compared with the current reference value generated by the outer loop, it is used to guide the converter to output specific active and reactive power. The core of PQ control is to decouple active power and reactive power so that they can be adjusted independently;

[0114] Step 2: Controller design;

[0115] Step 2.1: Design of power outer loop controller;

[0116] Step 2.2: Design of current inner loop controller;

[0117] Step 2.2.1: Design of variable gain superhelical ESO;

[0118] Step 2.2.2: Design of super-helical integral terminal sliding mode controller;

[0119] Step 3: Obtain the control output through the controller, use SPWM modulation to obtain the duty cycle, and apply the duty cycle to the control of the energy storage inverter switch tube, thereby realizing the signal control of the energy storage inverter.

[0120] Example 2

[0121] This embodiment provides an improved sliding mode anti-disturbance control method for a two-stage energy storage converter. Based on Embodiment 1, step 2.1 is specifically as follows:

[0122] The main function of the power outer loop is to ensure power conservation during the grid connection process of the converter and provide a reference value for the subsequent current inner loop. According to the instantaneous power theory, in order to make the three-phase energy storage converter close to unity power factor grid connection, the reactive current is always equal to 0. Under the condition of balanced three-phase grid voltage, the instantaneous values ​​of active power P and reactive power Q on the grid side of the three-phase energy storage converter are expressed as follows:

[0123]

[0124] From formula (4), we know that through i d and i q Control P and Q separately to achieve independent regulation of active power and reactive power; transform equation (4) to ref , Q ref When given, the d and q axis current reference values ​​are directly obtained by calculation; however, in order to eliminate the steady-state error, the PI regulator is introduced. After the deviation between P, Q and the P, Q command values ​​is adjusted by PI, the active current reference value i is obtained based on the instantaneous power theory and the dynamic response of the system P and Q. dref and reactive current reference value i qref , as shown below:

[0125]

[0126] In formula (5), P ref , Q ref For given active power and reactive power reference values, i dref 、i qref is the inner loop reference value of d and q axis current, k dp , k di is the d-axis PI adjustment parameter, k qp , k qi is the q-axis PI adjustment parameter.

[0127] Example 3

[0128] This embodiment provides an improved sliding mode anti-disturbance control method for a two-stage energy storage converter. Based on Embodiment 1-2, step 2.2 is as follows:

[0129] Step 2.2.1 is as follows:

[0130] First, define the state variable d and the q-axis current i d 、i q For x d1 、x q1 , from formula (3):

[0131]

[0132] In order to simplify the controller design difficulty, the inner loop coupling terms and unmodeled parts of the current of the d and q axes as well as the internal and external disturbances of the inner loop are regarded as the total disturbance of the inner loop, and are represented by f d1 、f q1 It means that the derivative of formula (3) is converted into the ADRC paradigm as follows:

[0133]

[0134] In formula (7), b d 、b q are the gains of the d-axis and q-axis control quantities respectively;

[0135] Since the value of b is generally unknown in actual engineering operations and cannot be accurately determined, we define b do 、b qo is the estimated value of the d and q axis control gain, let Formula (7) can be transformed into the following form:

[0136]

[0137] In formula (8), f d =(b d -b do )s d +f d1 , f q =(b q -b qo )s q +f q1 , b do 、b qo is the estimated value of the d and q axis control quantity gain;

[0138] f d , f q Expand to a new state variable z d3 , z q3 , the superhelical expansion state observer is designed as follows:

[0139]

[0140] In formula (9), z d1 For xd1 The estimated value of z q1 For x q1 The estimated value of z d2 , z q2 is the estimated value of the derivative, x d1 For x q1 The estimated value of the derivative; e d1 is the difference between the observed value and the actual value of the d-axis, e q1 is the difference between the observed value and the actual value of the q axis; z d3 is the total disturbance f including d-axis coupling, internal disturbance and unmodeled part. d The estimated value of z q3 is the total disturbance f including the q-axis coupling term, internal disturbance and unmodeled part. q The estimated value of β d1 , β d2 , β d3 , β q1 , β q2 , β q3 is the observer gain. When the observation error e of the superhelical ESO is close to 0, the expression of the observer is consistent with that of the linear extended state observer. Therefore, the bandwidth method is used for tuning as follows:

[0141] The value conditions of β1, β2, β3 are: β1 = 3ω0, β2 = 3ω0 2 , β3=ω0 3 .

[0142] In order to reduce system chattering and improve the observation capability of super-twisting expanded state observer to the total disturbance of the inner loop, a variable gain super-twisting ESO (VGST-ESO) is proposed. In order to reduce system chattering, the discontinuous switching term sign function in the super-twisting expanded state observer is replaced by a hyperbolic function. Secondly, a variable gain function that can change in real time with the observation error is designed to replace the linear gain in the super-twisting observer, so as to improve the observation capability to disturbance.

[0143] The switching function sign expression is:

[0144]

[0145] It can be seen from formula (10) that the sign function is a discontinuous function. When the sign function sign is used as the switching function of the super-helical sliding mode expansion state observer, discontinuous switching control characteristics will be generated along with the observation error, resulting in chattering problems and affecting the observation accuracy of the system. Therefore, a smooth hyperbolic function F(e i ) as the switching function of the observer.

[0146] Hyperbolic F(e i ) function is expressed as:

[0147]

[0148] Hyperbolic function F(e i ) and the image of the symbolic function sign(x) are compared as Figure 3 As shown, by formula (11) and Figure 2 It can be seen that the switching function F(e i ) is continuous and smooth, with no discontinuities, which can theoretically reduce the system chattering problem and improve the observation capability of generalized superhelical ESO to disturbances;

[0149] In order to improve the observer's ability to observe disturbances and increase the convergence speed of the system, a variable gain function that can change in real time with the observation accuracy is designed to replace the fixed value gain of ST-ESO;

[0150] The improved supercoil ESO expression is:

[0151]

[0152] In formula (12), z d1 For x d1 The improved estimate of the observer, z q1 For x q1 The improved estimate of the observer; d2 For x d1 The observer-improved estimate of the derivative, z q2 For x q1 The observer-improved estimate of the derivative; z d3 is the total disturbance f including coupling terms, internal disturbances and unmodeled parts. d The improved estimate of the observer, z q3 is the total disturbance f including coupling terms, internal disturbances and unmodeled parts. q The improved estimate of the observer; The improved variable gain function of the observer is as follows:

[0153]

[0154] The expression of variable gain L(t) is:

[0155]

[0156] In formula (14), η i , σ are both adjustable positive real numbers, and σ determines the observation accuracy of the improved superhelical ESO.

[0157] In order to meet the high-precision control design requirements of energy storage converters, a super-helical integral terminal sliding mode controller is introduced to replace the traditional sliding mode control. Compared with the traditional SMC, the super-helical algorithm can adjust the system state more efficiently and stably. In traditional sliding mode control, due to the existence of high-frequency switching quantity, the system may produce jitter phenomenon, while the integral terminal sliding mode uses integral to obtain the actual control quantity, which does not contain high-frequency switching quantity. Therefore, there is no jitter phenomenon in the system, which improves the stability and reliability of the system.

[0158] Therefore, in order to further improve the control performance of the system, the superhelical algorithm is combined with the integral terminal sliding mode idea, and a superhelical integral terminal sliding mode controller is designed, that is, step 2.2.2 is as follows:

[0159] Define the system state error d, the deviation between the actual current and the reference current of the q axis is e d 、e q :

[0160]

[0161] According to the current deviation e in formula (15), the integral terminal sliding surface S is designed as follows:

[0162]

[0163] In formula (16), α, β, λ, η are all positive numbers, 0<γ<1, p, q are positive odd numbers, and

[0164] Derivative the sliding surface S of formula (16) and substitute formula (8) into it, we can get:

[0165]

[0166] According to the equivalent control theory, The equivalent control law of the system is as follows:

[0167]

[0168] In order to weaken chattering and accelerate the system state to reach the sliding mode surface, the superhelical reaching law is introduced as the sliding mode switching control part. The superhelical control law consists of two parts, which are designed as follows:

[0169]

[0170] In formula (19), l1 and l2 are both constants greater than 0.

[0171] Combining equations (18) and (19) we can get the overall control law s of the system, which is expressed as follows:

[0172] s=seq +s sw (20)

[0173] Substituting the observed values ​​of the d-axis and q-axis variables of the ESO in equation (12), we can obtain the final control law of the converter: d ,s q for

[0174]

[0175] Step 3 uses SPWM (Sine Pulse Width Modulation), that is, sinusoidal pulse width modulation, to modulate the converter signal. Its basic working principle is as follows:

[0176] According to the controller designed by the control part, the obtained control signal is used as the modulation wave, and a high-frequency triangle wave is selected as the carrier. By comparing the size of the modulation wave and the carrier, the on-off state of the switch tube in the converter is determined. When the modulation wave is higher than the carrier, the switch tube is turned on; when the modulation wave is lower than the carrier, the switch tube is turned off. In this way, at the output end of the inverter circuit, a pulse sequence with a width that changes according to the sine law is obtained, that is, an SPWM wave.

[0177] Therefore, the converter control block diagram can be obtained as follows: Figure 4 shown.

[0178] Simulation and Experimental Analysis

[0179] In order to verify the effectiveness of the improved sliding mode anti-disturbance control method of the two-stage energy storage converter of the present invention, a corresponding simulation circuit is constructed in the MATLAB / Simulink simulation software, and it is compared and analyzed with the traditional PI control strategy. For simulation parameter settings, see Table 1. In the entire simulation process, a unified simulation environment and parameter configuration are used to ensure the fairness and accuracy of the comparison results.

[0180] Table 1 Circuit parameters

[0181] parameter Numeric Grid voltage amplitude e 311V <![CDATA[DC bus voltage U dc > 800V Filter inductor L 0.5mH Filter capacitor C 50μF Inductor parasitic resistance R 0.01Ω <![CDATA[DC regulated capacitor C dc > 1mF <![CDATA[DC side inductor L dc > 1mH Load power 30kW-80kW <![CDATA[Battery terminal voltage v bat > 500V Battery initial state of charge SOC 50％

[0182] In order to verify the advantages of the control method of the present invention over the traditional PI control strategy, the corresponding active power mutation is set in the simulation to intuitively compare the DC bus voltage response under different controls when facing dynamic changes. The simulation results are shown in Figure 2. Figure 5 shown.

[0183] Figure 5The figure shows the transient waveform diagram of the DC bus voltage when facing power jump under different control, and two active power jumps are set at 0.2s (P jumps from 30kW to 80kW) and 0.25s (P jumps from 80kW to 30kW). From the data analysis in the figure, it can be seen that under the PI control strategy, when the active power output of the energy storage converter jumps from 30kW to 80kW and from 80kW to 30kW, the DC bus voltage fluctuation caused is about 27V; at 0.3s, when the output power direction switches from 30kW to -30kW, the bus voltage fluctuates to 57V. In the three transient processes under the control method of the present invention, the DC bus voltage fluctuations are 8V, 7V and 32V respectively, which are significantly reduced compared with PI control. Therefore, in the case of active power jump, the method of the present invention has a better coping ability, can better cope with voltage fluctuations, significantly reduce overshoot, and ensure that the system continues to operate in a more stable and reliable state.

[0184] In order to further verify the superiority of the control method of the present invention over the existing control strategy, this paper adopts a hardware-in-the-loop (HIL) experimental platform. During the experiment, the corresponding active power mutation was set, and the performance differences of the two control strategies in dealing with dynamic changes were intuitively compared. The sampling frequency of the experiment was set to 20kHz to ensure the accuracy of data acquisition. First, a simulation circuit was constructed using Simulink to simulate the circuit control logic in the actual system; secondly, the constructed simulation circuit was imported into MT6020 and RCP1050 through the host computer to simulate the operating behavior and response of the actual hardware; finally, the real-time signal generated by the experimental platform was connected to the oscilloscope through the adapter board, and the oscilloscope was used to monitor and record the key data in the experimental process in real time, so as to facilitate subsequent data analysis and verification.

[0185] i d 、i b They represent the d-axis current on the AC side of the converter and the b-phase current in the three-phase stationary coordinate system, u dc is the DC bus voltage. To verify the performance of the control method of the present invention, it is compared with the PI control strategy. When the converter outputs active power of 30 kW and reactive power of 0, i d is 64.3A, i q When the output active power is 80kW and the reactive power is 0, i d is 171.5A, i q The calculation result can be used as a reference value for the experiment. The DC bus voltage u is set to 0A in steady state. dc is 800V, i d 、i b The accuracy is 100A / grid, u dcThe power jump test results under the two control strategies are shown in Figure 2. Figure 6-13 shown.

[0186] according to Figure 6-7 The data shows that under the PI control strategy, when the output active power of the energy storage converter jumps from 30kW to 80kW, the DC bus voltage u dc The overshoot is as high as 56V, and it gradually recovers to a stable state after a transient process of 36ms; d The current fluctuation caused by the jump from 65.3A to 172.4A produces an overshoot of 23A, and it returns to steady state after 25ms; the phase current i b The amplitude jumps from 65A to 172A, and after a 20ms transient process, it returns to steady-state operation. When the output power jumps from 80kW to 30kW, the DC bus voltage u dc The overshoot is 59V and the transition time is 33ms; d The overshoot caused by the current fluctuation is 22A, which jumps from 172.4A to 65.3A. After 24ms, the phase current i b The amplitude jumps from 172A to 65A, and recovers to steady-state operation after a transient process of 23ms.

[0187] according to Figure 8-9 It can be seen that under the control method of the present invention, the two power jumps cause i d The overshoot is almost 0, and the two transient processes, i d The transition time is 12ms and 11ms respectively. During the two power jumps, the DC bus voltage u dc The fluctuation amplitude is significantly reduced, the voltage fluctuation amplitude is only 8V and 5V, and the transient time is reduced to 7ms and 5ms, which is significantly shorter than PI control. Therefore, in the process of active power jump, the transient performance of the system is better under the control method of the present invention, and the system has better steady-state performance.

[0188] according to Figure 10-11 It can be seen that under the PI control strategy, when the energy storage converter outputs active power in a direction that switches from 30kW to -30kW, the DC bus voltage u dc The overshoot is as high as 76V, and gradually recovers to a stable state after a transient process of 33ms; the current direction switches, i d It jumps from 65.3A to -65.3A and returns to steady state after 11ms; the phase current i b After a 22ms transient process, it returns to steady state operation. When the output power jumps from -30kW to 30kW, u dc The overshoot is 73V and the transition time is 33ms; id The transition time from -65.3A to 65.3A is 18ms; the phase current i b After a transient process of 19ms, it returns to steady-state operation.

[0189] according to Figure 12-13 It can be seen that under the control method of the present invention, during the transient process of two active power direction switching, u dc The overshoot is 12V and 11V respectively, and the transition time is 9ms and 10ms respectively; i d The transition time to restore steady state is 9ms and 11ms respectively, and the phase current i b The transition time is 8ms. Compared with PI control, the system resumes steady-state operation under the control method of the present invention, the transient time is shorter, and the system fluctuation amplitude is smaller. Therefore, taking all factors into consideration, the control method of the present invention is superior to the traditional PI control strategy in terms of transient performance and chattering suppression.

[0190] In order to further verify the influence of control strategy on power quality, the Fourier analysis tool in Simulink is used to perform spectrum analysis of two steady-state cycles of grid-connected current, as shown in Figure 2. Figure 14-15 As shown. Figure 14-15 It can be seen that the harmonic distortion rate under the PI control strategy is 3.95%, and when the control method of the present invention is adopted, the harmonic distortion rate is reduced to 0.97%. The data shows that the control method of the present invention effectively suppresses the harmonic components that interfere with the power grid and can provide higher quality electric energy.

Claims

1. An improved sliding mode anti-disturbance control method for a two-stage energy storage converter, characterized in that: Firstly, a mathematical model of the energy storage converter is established in a three-phase stationary coordinate system and converted to a dq rotating coordinate system. The inner-loop coupling terms and unmodeled parts of the current on the d and q axes as well as the internal and external interferences of the inner loop are regarded as the total disturbances of the inner loop and expanded into new state variables. On this basis, it is converted into a second-order anti-disturbance paradigm. Then, a superhelical expanded state observer is designed, and the sign function of the discontinuous switching term in the superhelical expanded state observer is replaced by a hyperbolic function. A variable gain function that changes in real time with the observation error is designed to replace the linear gain of the ST-ESO. A superhelical integral terminal sliding mode is introduced as a feedback controller.

2. The improved sliding mode auto-disturbance rejection control method for a two-stage energy storage converter according to claim 1 is characterized in that: Follow the steps below to implement it: Step 1: Establish a mathematical model of the two-stage energy storage converter in the dq rotating coordinate system and convert it into a second-order active disturbance rejection paradigm; Step 2: Controller design; Step 2.1: Design of power outer loop controller; Step 2.2: Design of current inner loop controller; Step 2.2.1: Design of variable gain superhelical ESO; Step 2.2.2: Design of super-helical integral terminal sliding mode controller; Step 3: Obtain the control output through the controller, use SPWM modulation to obtain the duty cycle, and apply the duty cycle to the control of the energy storage converter switch tube, thereby realizing the signal control of the energy storage converter.

3. The improved sliding mode auto-disturbance rejection control method for a two-stage energy storage converter according to claim 2 is characterized in that: The step 1 specifically comprises: During the grid-connected operation of the energy storage converter, the working states of the two switches in each bridge arm are complementary. Therefore, the switching function is defined as follows: In formula (1), j = a, b, c, representing the three phases a, b, and c of the AC power grid; According to Kirchhoff's law, the voltage and current relationship equation of the energy storage converter in the abc three-phase stationary coordinate system is: In formula (2), u a 、u b 、u c is the three-phase voltage on the AC side of the two-stage energy storage converter; i sa 、i sb 、i sc is the three-phase current on the AC side; e a 、e b 、e c is the AC grid voltage; L is the filter inductance; C dc is the DC side capacitance parameter; R is the line equivalent resistance parameter; i r is the DC side converter output current; u dc 、i C is the DC bus voltage and current; s ka 、s kb 、s kc They are the switch control signals of the three-phase bridge arms a, b and c respectively; Performing Park transformation on equation (2), we can obtain the mathematical model of the converter in the dq coordinate system: In formula (3), ω is the angular frequency of the grid voltage; e d 、i d 、s d They are the grid voltage, current, and switching function of the d-axis, and the e-axis q 、i q 、s q are the grid voltage, current and switch function of the q axis respectively; L is the filter inductance; u dc 、i C is the DC bus voltage and current.

4. The improved sliding mode auto-disturbance rejection control method for a two-stage energy storage converter according to claim 3 is characterized in that: The step 2.1 is specifically as follows: According to the instantaneous power theory, in order to make the three-phase energy storage converter close to unity power factor grid connection, the reactive current is always equal to 0. Under the condition of balanced three-phase grid voltage, the instantaneous values ​​of active power P and reactive power Q on the grid side of the three-phase energy storage converter are expressed as: From formula (4), we know that through i d and i q Control P and Q separately to achieve independent regulation of active power and reactive power; Transform equation (4) and when P ref , Q ref When given, the d and q axis current reference values ​​are directly obtained by calculation; however, in order to eliminate the steady-state error, the PI regulator is introduced. After the deviation between P, Q and the P, Q command values ​​is adjusted by PI, the active current reference value i is obtained based on the instantaneous power theory and the dynamic response of the system P and Q. dref and reactive current reference value i qref , as shown below: In formula (5), P ref , Q ref For given active power and reactive power reference values, i dref 、i qref is the inner loop reference value of d and q axis current, k dp , k di is the d-axis PI adjustment parameter, k qp , k qi is the q-axis PI adjustment parameter.

5. The improved sliding mode auto-disturbance rejection control method for a two-stage energy storage converter according to claim 4 is characterized in that: The step 2.2.1 is specifically as follows: First, define the state variables d and q-axis current i d 、i q For x d1 、x q1 , from formula (3): The inner loop coupling terms and unmodeled parts of the current in the d and q axes as well as the internal and external disturbances of the inner loop are regarded as the total disturbance of the inner loop, and are expressed as f d1 、f q1 It means that the derivative of formula (3) is converted into the ADRC paradigm as follows: In formula (7), b d 、b q are the gains of the d-axis and q-axis control quantities respectively; Definition b do , b qo is the estimated value of the d and q axis control gain, let Transform formula (7) into: In formula (8), f d =(b d -b do )s d +f d1 , f q =(b q -b qo )s q +f q1 , b do , b qo is the estimated value of the d and q axis control quantity gain; f d 、f q Expand to new state variables z d3 、z q3 , the superhelical expansion state observer is designed as follows: In formula (9), z d1 For x d1 The estimated value of z q1 For x q1 The estimated value of z d2 , z q2 is the estimated value of the derivative, x d1 For x q1 The estimated value of the derivative; e d1 is the difference between the observed value and the actual value of the d-axis, e q1 is the difference between the observed value and the actual value of the q axis; z d3 is the total disturbance f including d-axis coupling, internal disturbance and unmodeled part. d The estimated value of z q3 is the total disturbance f including the q-axis coupling term, internal disturbance and unmodeled part. q The estimated value of β d1 , β d2 , β d3 , β q1 , β q2 , β q3 is the observer gain. When the observation error e of the superhelical ESO is close to 0, the expression of the observer is consistent with that of the linear extended state observer. Therefore, the bandwidth method is used for tuning as follows: The value conditions of β1, β2, and β3: β1 = 3ω0, β2 = 3ω0 2 , β3 = ω0 3 ; In order to reduce system chattering and improve the observation capability of the superhelical extended state observer to the total disturbance of the inner loop, a variable gain superhelical ESO is proposed, and the sign function of the discontinuous switching term in the superhelical extended state observer is replaced by a hyperbolic function; secondly, a variable gain function that changes in real time with the observation error is designed to replace the linear gain of the ST-ESO, so as to improve the observation capability of the disturbance; The switching function sign expression is: From formula (10), we know that the sign function is a discontinuous function. When the sign function sign is used as the switching function of the super-helical sliding mode expansion state observer, discontinuous switching control characteristics will be generated along with the observation error, resulting in chattering problems and affecting the observation accuracy of the system. Therefore, a smooth hyperbolic function F(e i ) as the switching function of the observer; Hyperbolic F(e i ) function is expressed as: The improved supercoil ESO expression is: In formula (12), z d1 For x d1 The improved estimate of the observer, z q1 For x q1 The improved estimate of the observer; d2 For x d1 The observer-improved estimate of the derivative, z q2 For x q1 The observer-improved estimate of the derivative; z d3 is the total disturbance f including coupling terms, internal disturbances and unmodeled parts. d The improved estimate of the observer, z q3 is the total disturbance f including coupling terms, internal disturbances and unmodeled parts. q The improved estimate of the observer ; The improved variable gain function of the observer is as follows: The expression of variable gain L(t) is: In formula (14), η i , σ are both adjustable positive real numbers, and σ determines the observation accuracy of the improved superhelical ESO.

6. The improved sliding mode auto-disturbance rejection control method for a two-stage energy storage converter according to claim 5 is characterized in that: The step 2.2.2 is specifically as follows: Define the system state error d, the deviation between the actual current and the reference current of the q axis is e d 、e q : According to the current deviation e in formula (15), the integral terminal sliding surface S is designed as follows: In formula (16), α, β, λ, η are all positive numbers, 0<γ<1, p, q are positive odd numbers, and Derivative the sliding surface S of formula (16) and substitute formula (8) into it to obtain: According to the equivalent control theory, The equivalent control law of the system is as follows: In order to weaken chattering and accelerate the system state to reach the sliding mode surface, the superhelical reaching law is introduced as the sliding mode switching control part. The superhelical control law consists of two parts, which are designed as follows: In formula (19), l1 and l2 are both constants greater than 0; Combining equations (18) and (19), we get the overall control law s of the system, which is expressed as follows: s=s eq +s sw (20) Substituting the observed values ​​of the ESO d-axis and q-axis variables in equation (12), we can obtain the final converter control law s d 、s q for

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