In this paper, a high-order nonlinear disturbance observer-based fractional-order sliding mode control (FOSMC) strategy is proposed for DC/DC buck converters in the presence of mismatched disturbances, ensuring the properties of both stability and dynamic performance. Traditional sliding mode control can deal with matched disturbances while achieving desired closed-loop performance, unfortunately it is particularly sensitive to mismatched disturbances. In the proposed control structure, two nonlinear disturbance observers are constructed to estimate both matched and mismatched disturbances in finite time. Then, the estimated variables are used for the fractional-order sliding mode surface design, where a super twisting sliding mode controller is designed to drive the states of the system to track their desired values. Comparing with the traditional SMC, the proposed method not only reduces the sensitivity of the system to mismatched disturbance, but also improves the transient performance of the system. Simulation and experimental results have comprehensively illustrated the feasibility and effectiveness of the proposed strategy.

Fractional-Order Sliding Mode Approach of Buck Converters With Mismatched Disturbances

An intelligent adaptive control of DC–DC power buck converters

This work proposes a modified high gain DC‐DC converter integrated with two boost converter stages, based on a boost cell and a Z‐source (ZS) cell with a switched capacitor (SC). The proposed converter architecture is simple, with a continuous input current and a wide range of input voltage fluctuation handling capabilities. It also provides a high voltage gain while minimizing voltage stress on semiconductor components. Because of the aforementioned characteristics, the proposed converter is suitable for combining with low‐voltage DC‐sources to high‐voltage DC bus in a variety of applications such as solar photovoltaic (SPV), fuel‐cell, and LED lighting. The operational principles, thermal modeling, steady‐state, and dynamic performance analysis are meticulously carried out on a 400 W laboratory prototype of the proposed converter. The converter's performance is carefully compared with similar existing topologies in terms of total device count and size, the voltage stress on power semiconductors, voltage gain, and peak efficiency. Furthermore, experimental findings show that a 12 V input is boosted to 98.8 V at a duty ratio of 0.3, demonstrating the efficacy of the proposed converter over a comparable structure.

A modified Z‐source switched‐capacitor based non‐isolated high gain DC‐DC converter for photovoltaic applications

This article considers a problem of tracking, convergence of disturbance observer (DO) based optimal control design for uncertain surface vessels (SVs) with external disturbance. The advantage of proposed optimal control using adaptive/approximate reinforcement learning (ARL) is that consideration for whole SVs with only one dynamic equation and without conventional separation technique. Additionally, thanks to appropriate disturbance observer, the attraction region of tracking error is remarkably reduced. On the other hand, the particular case of optimal control problem is presented by directly solving for the purpose of choosing the suitable activation functions of ARL. Furthermore, the proposed ARL based optimal control also deals with non-autonomous property of closed tracking error SV model by considering the equivalent system. Based on the Lyapunov function candidate using optimal function and quadratic form of estimated error of actor/critic weight, the stability and convergence of the closed system are proven. Some examples are given to verify and demonstrate the effectiveness of the new control strategy. 

Disturbance observer-based adaptive reinforcement learning for perturbed uncertain surface vessels.

The problem of voltage regulation in unknown constant resistive loads is addressed in this paper from the nonlinear control point of view for second-order DC-DC converters. The converters’ topologies analyzed are: (i) buck converter, (ii) boost converter, (iii) buck-boost converter, and (iv) non-inverting buck-boost converter. The averaging modeling method is used to model these converters, representing all these converter topologies with a generalized port-Controlled Hamiltonian (PCH) representation. The PCH representation shows that the second-order DC-DC converters exhibit a general bilinear structure which permits to design of a passivity-based controller with PI actions that ensures the asymptotic stability in the sense of Lyapunov. A linear estimator based on an integral estimator that allows reducing the number of current sensors required in the control implementation stage is used to determine the value of the unknown resistive load. The main advantage of this load estimator is that it ensures exponential convergence to the estimated variable. Numerical simulations and experimental validations show that the PI passivity-based control allows voltage regulation with first-order behavior, while the classical PI controller produces oscillations in the controlled variable, significantly when the load varies.

Sensorless Adaptive Voltage Control for Classical DC-DC Converters Feeding Unknown Loads: A Generalized PI Passivity-Based Approach.

In this paper, four control strategies for DC-DC buck converters are proposed, compared and analyzed: a single-loop adaptive control strategy (SA), a double-loop adaptive control strategy (DA), a single-loop disturbance observer-based control strategy (SDOB) and a double-loop disturbance observer-based control strategy (DDOB). First, the nominal system without considering the parametric uncertainties of the DC-DC buck converter is built to help develop the SA and DA. The SA is built by adaptive and backstepping control approaches, and the DA is set up by adaptive and sliding mode control approaches. Additionally, a model considering parametric uncertainties is introduced, giving the opportunity to develop the SDOB and DDOB. The SDOB is developed using a designed disturbance observer and backstepping control technique, and the DDOB is synthesized using a designed disturbance observer and sliding mode control method. Finally, the advantages and disadvantages of the four proposed control strategies are compared and analyzed through experiments.

Advanced Control Strategies for DC–DC Buck Converters With Parametric Uncertainties via Experimental Evaluation

In this paper, a second-order continuous sliding mode back electromotive force (EMF) observer is proposed for sensorless permanent magnet synchronous motor (PMSM) control. Compared to traditional first-order and super twisting sliding mode observer, the proposed strategy can maintain the characteristics of the second-order observer and also smooth the estimated back EMF. Third-order linear extended observer (LESO) is adopted to estimated the position, speed and load torque of PMSM. Compared to arc-tangent function method, LESO does not use low-pass filter, and is less sensitive to high-frequency noise in the estimated back EMF. Meanwhile, the estimated load torque can be used as disturbance compensation for subsequent control. Simulation results have comprehensively illustrated the feasibility and effectiveness of the proposed strategy.

Xinpo Lin

Papers

Fractional-Order Sliding Mode Approach of Buck Converters With Mismatched Disturbances

Advanced Control Strategies for DC–DC Buck Converters With Parametric Uncertainties via Experimental Evaluation

A Second-order Continuous Sliding Mode Observer for Sensorless Permanent Magnet Synchronous Motor Control