A discrete adaptive sliding mode based compound control method for dc-buck converter

Abstract

This invention proposes a composite control method for DC-DC buck converters based on discrete adaptive sliding mode control. In DC-DC buck converter systems, not only are there constant / slowly varying disturbances, but also Gaussian noise. This method additionally models, analyzes, and processes the noise, proposing an adaptive Kalman filter and disturbance observer (AKF+DOB) strategy in the discrete domain, and further suppressing disturbances through an adaptive discrete sliding mode controller (ADSMC). The discrete composite controller designed in this invention exhibits strong robustness to various disturbances and uncertainties even under strong noise conditions, effectively improving the anti-interference, noise suppression performance, and output accuracy of the DC-DC buck converter system.

Description

Technical Field

[0001] This invention relates to a composite control technology for DC-DC buck converters based on discrete adaptive sliding mode, belonging to the field of advanced control technology for power electronic systems. Background Technology

[0002] With the continuous development and advancement of smart grids and renewable energy technologies, DC-DC converter systems, as core components of power conversion, have received increasing attention and research. Due to their advantages such as low cost, high efficiency, and high reliability, DC-DC converter systems are widely used in various electromechanical systems, such as DC microgrid systems, servo drive systems, and space systems. However, with increasingly stringent control requirements, especially in complex internal and external environments and under time-varying interference conditions, ensuring high accuracy in voltage tracking, rapid dynamic response, and strong anti-interference capabilities has become a core issue restricting their performance.

[0003] Improving the anti-interference performance of DC-DC circuits has significant theoretical and practical value, playing a crucial role in enhancing the performance and reliability of electronic equipment. Currently, advanced control algorithms for DC-DC buck converter systems have attracted widespread attention. Early research focused primarily on solutions based on linear controllers, such as PID control, which are widely used in scenarios requiring high real-time performance and low computational complexity. However, due to the influence of multi-source time-varying disturbances and parameter uncertainties, conventional linear controllers often cannot simultaneously handle both large and small deviations, making it difficult to achieve satisfactory control results. Subsequent research has mainly focused on advanced nonlinear control strategies. Numerous nonlinear solutions have been widely applied in converter systems, such as backstepping control, adaptive control, and model predictive control. These nonlinear control strategies improve the control performance of converter systems from different perspectives.

[0004] Besides the above-mentioned schemes, sliding mode control (SMC) has been widely studied and applied due to its simple control structure and strong robustness against disturbances and uncertainties. In the literature (Tan SC, Lai YM, Chi KT. General design issues of sliding-mode controllers in DC–DC converters[J].IEEE Transactions on Industrial Electronics, 2008, 55(3):1160-1174.), a sliding mode controller based on a linear sliding surface was used to solve the disturbance suppression problem in a DC-DC buck converter system, achieving fast tracking of the output voltage and effective suppression of matching disturbances. Because traditional sliding mode uses discontinuous switching terms, it is easy to cause high-frequency chattering in the control quantity, resulting in large output voltage fluctuations. Accurate disturbance estimation and fine compensation are widely used as an effective scheme to suppress chattering. To achieve faster voltage tracking response, a non-singular terminal sliding-mode control scheme based on a finite-time observer was designed and implemented in the literature (Komurcugil H. Non-singular terminal sliding-mode control of DC–DC buckconverters[J]. Control Engineering Practice, 2013, 21(3):321-332.). The results show that the non-singular terminal sliding-mode design can achieve finite-time tracking of the reference voltage by the converter system. Higher-order sliding-mode control schemes have also been widely studied and applied in converter systems due to their higher tracking accuracy and chatter suppression effect. However, it is worth noting that the above sliding-mode control schemes are all based on continuous-time domain analysis and design, without considering the digital implementation of the controller.

[0005] Thanks to the rapid development of microelectronic hardware, digital microprocessors are increasingly being used in practical engineering. Due to the limitation of their sampling period, sliding mode controllers designed based on continuous time domain inevitably experience performance degradation and loss after discretization. Therefore, the design and analysis of discrete-time sliding mode control (DSMC) has received widespread attention from researchers and engineers. The literature (Ma H, Wu J, Xiong Z. Discrete-time sliding-mode control with improved quasi-sliding-mode domain[J].IEEE Transactions on Industrial Electronics,2016,63(10):6292-6304.) proposes a discrete sliding mode control scheme based on arrival law, which solves the problem of excessive energy in equivalent control. However, due to the existence of discontinuous terms, the controller can also cause high-frequency chattering of the output voltage. At present, the main methods to eliminate chattering are the saturation function method, the adaptive reaching law method, and the disturbance feedforward compensation. However, using the saturation function sacrifices the anti-interference ability to obtain the continuity of the control signal.

[0006] Suppressing disturbances and uncertainties is also one of the key objectives in the design of discrete control systems. An effective way to solve this problem is to design an observation mechanism to estimate disturbances or uncertainties and then perform corresponding feedforward compensation. Therefore, a control scheme based on a discrete disturbance observer can improve tracking performance while retaining the original controller's anti-disturbance capability.

[0007] Currently, the most common discrete disturbance observation method uses delay estimation. This method has a simple structure and high estimation accuracy for slow time-varying disturbances. However, it fails to yield satisfactory results for fast time-varying disturbances. Furthermore, under noisy conditions, this method can amplify the noise. Additionally, continuous observers can be discretized into discrete observers, such as discrete PI observers, discrete ESO observers, and discrete sliding mode observers. Due to limited sampling, the performance of these observers also degrades. To further improve the accuracy of disturbance estimation, this paper designs a discrete observer based on recursion, effectively handling rapidly changing disturbances.

[0008] The literature (Sun H, Madonski R, Li S, et al. Composite control design for systems with uncertainties and noise using combined extended state observer and Kalman filter[J]. IEEE Transactions on Industrial Electronics, 2021, 69(4): 4119-4128.) considers both interference and noise, and proposes an ESO+KF structure. While the high gain of the ESO can lead to faster convergence, it also makes it sensitive to noise. Therefore, the ESO+KF can effectively solve this problem. However, in terms of the controller, state feedback is used, resulting in weak anti-interference capability. Summary of the Invention

[0009] The technical problem this invention aims to solve is that DC-DC buck converter systems not only suffer from constant / slowly varying disturbances but also from Gaussian noise. Without modeling, analyzing, and processing the noise, the control performance often falls short of expectations. Therefore, to address the existing disturbance and noise issues, an adaptive Kalman filter and disturbance observer (AKF+DOB) strategy is proposed in the discrete domain. The controller section employs an adaptive discrete sliding mode controller (ADSMC) to further suppress disturbances. This composite control method ensures strong anti-interference performance and noise suppression capabilities, improving the robustness, dynamic response, and steady-state accuracy of the DC-DC buck converter system.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] Step 1, establish the discrete-domain mathematical model of the DC-DC buck converter as follows:

[0012] 1) By writing the current and voltage equations for the DC-DC buck converter system, the continuous domain model of the system can be obtained:

[0013]

[0014] Where w is the lumped disturbance. x = [x1 x2].

[0015] 2) When the controller u is digitally implemented using a zero-order hold (ZOH), i.e., for t∈[kT,(k+1)T], u(t)=u(kT), where T is the sampling period, the system in 1) can be described in the following discrete form:

[0016] x k+1 =Φx k +Γuk +d k

[0017] Where x k Representing x(kT), Φ=e AT ,

[0018] Step 2, based on the mathematical model in Step 1, model the interference and noise as follows:

[0019] x k+1 =Φx k +Γu k +d k +w k

[0020] y k =x k +v k

[0021] d k For constant / slowly varying disturbances, w k ,v k It is divided into model noise and measurement noise, and w k ,v k Satisfying probability distribution w k ~N(0,Q),v k ~N(0,R).

[0022] In step 3, based on the mathematical models in steps 1 and 2, an adaptive Kalman filter and disturbance observer are designed to address noise and interference as follows:

[0023] 1) Adaptive Kalman Filter

[0024] The covariance matrix of prior estimates and prior errors:

[0025]

[0026]

[0027] Kalman gain:

[0028]

[0029] Posterior estimation and posterior error covariance matrix:

[0030]

[0031]

[0032] Covariance adaptive update with forgetting factor:

[0033]

[0034]

[0035]

[0036] The forgetting factor is 0 < α < 1.

[0037] 2) Disturbance Observer

[0038]

[0039]

[0040] Where the observer gain matrix

[0041] Step 4, based on the obtained disturbance estimate and posterior state estimation The sliding surface and discrete adaptive sliding controller designed to address mismatch interference are as follows:

[0042] 1) The sliding surface is designed to address mismatch interference as follows:

[0043]

[0044] Among them, C s = [c 1], c > 0, For disturbance estimation, This is the posterior estimate of the state.

[0045] 2) Discrete Adaptive Sliding Mode Controller

[0046] s k+1 Defined as

[0047]

[0048] in Discrete adaptive sliding mode controller is

[0049]

[0050] in

[0051] In step 5, the control signal u is processed to obtain the PWM duty cycle signal, which drives the DC-DC buck converter circuit to complete the output voltage anti-interference control. A simulation platform is built in the Matlab Simulink environment to verify the above control algorithm.

[0052] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0053] 1. This invention applies a composite control method based on discrete adaptive sliding mode to a DC-DC buck converter, which can improve the converter system's anti-interference capability, noise suppression capability, dynamic response performance, and steady-state accuracy. First, the adaptive filter (AKF) can suppress high-frequency noise in the system and dynamically update the covariance matrix to adapt to changes in the external environment, ensuring optimal filtering performance. Second, the disturbance observer (DOB) estimates constant / slowly varying disturbances in real time for disturbance feedforward compensation and AKF model updates, thereby enhancing the system's anti-interference performance. Therefore, in environments with large disturbances and strong noise, the AKF+DOB structure can also ensure higher output accuracy compared to traditional controllers.

[0054] 2. This invention applies a composite control method based on discrete adaptive sliding mode to DC-DC buck converters, effectively addressing both matched and unmatched interference issues. Compared to traditional controllers, this invention embeds unmatched interference into the sliding surface design, thus resolving the unmatched interference problem at the algorithmic level. Therefore, it ensures higher dynamic response performance and steady-state accuracy when facing both matched and unmatched interference. Attached Figure Description

[0055] Figure 1 This is a block diagram of the composite control of the DC-DC buck converter based on discrete adaptive sliding mode according to the present invention.

[0056] Figure 2 It is the sudden addition of unmatched interference d1 and interference estimation. Line graph.

[0057] Figure 3 It is the sudden addition of matched interference d2 and interference estimation Line graph.

[0058] Figure 4 The graphs show the system output comparisons using different algorithms. The three algorithms are: Discrete Adaptive Sliding Mode + Interference Observer + Low-Pass Filter (ADSMC+DOB+LPF), Discrete Adaptive Sliding Mode + Interference Observer + Kalman Filter (ADSMC+DOB+KF), and Discrete Adaptive Sliding Mode + Interference Observer + Adaptive Kalman Filter + Sliding Surface with Mismatch (ADSMC+DOB+AKF).

[0059] Figure 5 It is a curve comparing the measured values ​​of the system state with the actual system output values.

[0060] Figure 6 It is a system phase diagram. Detailed Implementation

[0061] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0062] A composite control method for a DC-DC buck converter based on discrete adaptive sliding mode, comprising the following steps:

[0063] Step 1: Establish a discrete-domain mathematical model of the DC-DC buck converter;

[0064] Step 2: Based on the mathematical model in Step 1, perform modeling and analysis of interference and noise;

[0065] Step 3: Based on the mathematical models in Step 1 and Step 2, design an adaptive Kalman filter and a disturbance observer to address noise and interference.

[0066] Step 4: Obtain the disturbance estimate through Step 3. and posterior state estimation Simultaneously, a sliding mode surface and a discrete adaptive sliding mode controller are designed to address mismatched interference, thereby realizing the DC converter control law under strong interference and noise.

[0067] Step 5: Build the relevant simulation platform in the Matlab / simulink simulation environment to perform simulation verification of the above control algorithm.

[0068] The specific steps described above are explained below:

[0069] Step 1, establish the discrete-domain mathematical model of the DC-DC buck converter as follows:

[0070] 1) Write the current and voltage equations for the DC-DC buck converter system as follows:

[0071]

[0072] Where μ∈[0,1] represents the PWM duty cycle. w1 and w2 are concentrated disturbances caused by perturbations of the L, C, R, and E parameters.

[0073] Let x1 = v o -v r , The continuous domain model of the system can be obtained as follows:

[0074]

[0075] Where w is the lumped disturbance. x = [x1 x2] T .

[0076] 2) When the controller u is digitally implemented using a zero-order hold (ZOH), i.e., for t∈[kT,(k+1)T], u(t)=u(kT), where T is the sampling period, the system in 1) can be described in the following discrete form:

[0077] x k+1 =Φx k +Γu k +d k

[0078] Where x k Representing x(kT), Φ=e AT ,

[0079] Step 2, based on the mathematical model in Step 1, model the interference and noise as follows:

[0080] x k+1 =Φx k +Γu k +d k +w k

[0081] y k =x k +v k

[0082] d k For constant / slowly varying disturbances, w k ,v k It is divided into model noise and measurement noise, and w k ,v k Satisfying probability distribution w k ~N(0,Q),v k ~N(0,R).

[0083] In step 3, based on the mathematical models in steps 1 and 2, an adaptive Kalman filter and disturbance observer are designed to address noise and interference as follows:

[0084] 1) Adaptive Kalman Filter

[0085] The covariance matrix of prior estimates and prior errors:

[0086]

[0087]

[0088] Kalman gain:

[0089]

[0090] Posterior estimation and posterior error covariance matrix:

[0091]

[0092]

[0093] Covariance adaptive update with forgetting factor:

[0094]

[0095]

[0096]

[0097] The forgetting factor is 0 < α < 1.

[0098] 2) Disturbance Observer

[0099]

[0100]

[0101] Where v k For intermediate process dummy variables, For interference estimates, Let λ be the observer gain matrix. i ∈(0,1),i=1,2.

[0102] Step 4, based on the obtained disturbance estimate and posterior state estimation The sliding surface and discrete adaptive sliding controller designed to address mismatch interference are as follows:

[0103] 1) To address the mismatch interference, the sliding surface is designed as follows:

[0104]

[0105] Among them, C s = [c 1], c > 0, For disturbance estimation, This is the posterior estimate of the state.

[0106] 2) Discrete Adaptive Sliding Mode Controller

[0107] s k+1 Defined as

[0108]

[0109] in

[0110] Discrete adaptive sliding mode controller is

[0111]

[0112] in

[0113] In step 5, the control signal u is processed to obtain the PWM duty cycle signal, which drives the DC-DC buck converter circuit to complete the output voltage anti-interference control. A simulation platform is built in the Matlab Simulink environment to verify the above control algorithm. The simulation parameters are set as follows:

[0114] Table 1 System Parameters

[0115] capacitance C <![CDATA[3*10 -6 F]]> inductance L <![CDATA[3*10 -6 H]]> load R 100Ω Control cycle T 0.0001s

[0116] The simulation test was conducted under two operating conditions: matched interference d2 and unmatched interference d1. D2 was suddenly subjected to a step-matched interference at 100ms, and D1 was suddenly subjected to an unmatched interference at 300ms. Simultaneously, the system exhibited significant measurement noise. The system interferences and their observed values ​​are as follows: Figure 2 , Figure 3 .

[0117] In the simulation results, the proposed scheme is Discrete Adaptive Sliding Mode Filter (ADSMC) + Disturbance Observer + Adaptive Kalman Filter + Sliding Surface with Mismatch Terms (DOB + AKF). To demonstrate the superiority of this invention, the algorithm is also compared with Discrete Adaptive Sliding Mode Filter (ADSMC + DOB + LPF) and Discrete Adaptive Sliding Mode Filter (ADSMC + DOB + KF), such as... Figure 4 As shown.

[0118] The performance improvements brought about by this invention are specifically manifested in the following ways: a) The sliding surface with non-matching terms proposed in this invention can ensure accurate output even in the presence of non-matching disturbances. b) Compared with the KF algorithm, the AKF strategy proposed in this invention can adaptively and dynamically adjust the system covariance parameter, better adapt to environmental changes, and reduce output overshoot caused by sudden addition / removal of disturbances. c) Compared with conventional methods, the algorithm proposed in this invention can better suppress noise, such as... Figure 5 As shown.

[0119] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A discrete adaptive sliding mode based compound control method for DC buck converter, characterized in that, The specific steps include: Step 1: Establish a discrete-domain mathematical model of the DC-DC buck converter; Step 2: Based on the mathematical model in Step 1, perform modeling and analysis of interference and noise; Step 3: Based on the mathematical models in Step 1 and Step 2, design an adaptive Kalman filter and a disturbance observer to address noise and interference. Step 4: Obtain the disturbance estimate through Step 3. and posterior state estimation Meanwhile, a sliding surface and a discrete adaptive sliding mode controller are designed to address mismatch interference, thereby realizing the DC converter control law under strong interference and noise. Step 5: Build the relevant simulation platform in the Matlab / Simulink simulation environment to verify the above control method through simulation. In step 3, based on the mathematical models in steps 1 and 2, an adaptive Kalman filter and disturbance observer are designed to address noise and interference as follows: 1) Adaptive Kalman Filter Prior estimates and the covariance matrix of prior errors: Kalman gain: Posterior estimation and posterior error covariance matrix: Covariance adaptive update with forgetting factor: Among them, forgetting factor ; 2) Disturbance Observer Where the observer gain matrix , ; In step 4, based on the obtained disturbance estimate and posterior state estimation The sliding surface and discrete adaptive sliding controller designed to address mismatch interference are as follows: 1) The sliding surface is designed to address mismatch interference as follows: in, , , For disturbance estimation, For posterior state estimation; 2) Discrete Adaptive Sliding Mode Controller Defined as: in ; The discrete adaptive sliding mode controller is: in .

2. The composite control method for a DC-DC buck converter based on discrete adaptive sliding mode according to claim 1, characterized in that, In step 1, the discrete-domain mathematical model of the DC-DC buck converter is established as follows: 1) By writing the current and voltage equations for the DC-DC buck converter system, the continuous domain model of the system can be obtained: Where w is the lumped disturbance. ; 2) When the controller u is digitally implemented using a zero-order hold, i.e., for , Where T is the sampling period, the system in 1) is described in the following discrete form: in represent , .

3. The composite control method for a DC-DC buck converter based on discrete adaptive sliding mode according to claim 1, characterized in that, In step 2, based on the mathematical model in step 1, the interference and noise are modeled as follows: in For constant or slowly varying disturbances, It is divided into model noise and measurement noise, and at the same time Satisfy probability distribution .

4. The composite control method for a DC-DC buck converter based on discrete adaptive sliding mode according to claim 1, characterized in that, In step 5, the control signal u is processed to obtain the PWM duty cycle signal, which drives the DC-DC buck converter circuit to complete the output voltage anti-interference control. A relevant simulation platform is built in the Simulink environment of Matlab to simulate and verify the above control method.

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