Equivalent Control Approach Research Articles

Integral sliding mode based direct power control of isolated DC‐DC converter for improved voltage regulation

AbstractThis article presents an isolated bidirectional DC‐DC dual active bridge (DAB) converter with an integral sliding mode‐based direct power control (SM‐DPC). Maintaining the dc‐link stability and obtaining a robust control for the converter during sudden load change is a significant challenge. The sliding mode control is well known for its robustness, stability, and tracking performance. The sliding surface based on output voltage error is selected, while the proposed method utilizes the equivalent control approach to generate the power reference for the DAB converter. The direct power control provides an easy control method for the DAB converter as the output voltage depends on the transmitted power, governed by the phase shift angle of two H‐bridges of the converter. The proposed method enhances the steady‐state performance and renders a fast transient response under load change and input voltage variation. Moreover, the method avoids complicated converter modeling and utilizes the voltage dynamic equation and power transfer equation for the controller design. The controller performance and effectiveness are validated with experimental results for a 2‐kW DAB converter.

Discrete-Time Sliding Mode Control Design for Unicycle Robot With Bounded Inputs

This brief focuses on the stabilization of a unicycle mobile robot subject to actuator saturation. A discrete-time sliding mode (DSM) controller is designed based on equivalent control approach, for the multirate sampled equivalent model of the chained form of unicycle mobile robot. The sliding variables are so chosen as to guarantee the convergence of the system states to the origin in finite time. The adopted equivalent control approach in conjunction with the choice of the sliding variables guarantees finite-time stabilization of the unicycle robot, in the presence of saturating control inputs. A characterization of the domain of attraction (DOA) is also provided in terms of the convergence parameters. The efficacy of the proposed design is validated through simulations.

Fixed frequency integral sliding‐mode current‐controlled MPPT boost converter for two‐stage PV generation system

In two-stage grid-integrated photovoltaic (PV) system, usually a DC-DC converter is employed between the PV modules and the inverter. The dynamic interactions between the DC-DC converter, inverter, and the maximum power point tracking (MPPT) controller may affect the system performances. This study gives an integral procedure to design a stable sliding-mode controller (SMC) based on fixed frequency equivalent control approach to improve the transient response of PV system and to track the reference voltage supplied by the voltage-oriented MPPT controller in the presence of environmental and load perturbations and converter output sinusoidal perturbations imposed by the second harmonic of the grid frequency. The controller consists of fast current tracking inner current loop based on SMC law whose sliding surface is defined by the input capacitor and inductor current and outer PI controller maintains required PV voltage regulation. The superiority of the controller is validated at different operating conditions through PSIM software and its performance is compared with variable frequency hysteresis-based SMC. To check the static and transient performances of the system, various experiments are conducted. The results obtained show very fast transient response in settling time and alleviation of chattering magnitude at various operating conditions.

Fixed- and variable-frequency sliding mode controller–maximum power point tracking converter for two-stage grid-integrated photovoltaic system employing nonlinear loads with power quality improvement features

This article presents a reliable and efficient photovoltaic sliding mode voltage-controlled maximum power point tracking DC-DC converter–active power filter integration system to supply real power to grid. This integrated active power filter system performs power quality enhancement features to compensate current harmonics to make distortion-free grid supply current and reactive power employing nonlinear loads. The proposed proportional–integral–derivative–based sliding mode controller is designed with fixed-frequency pulse-width modulation based on equivalent control approach. The main objective of this paper is to design a photovoltaic system with a new sliding surface to force the photovoltaic voltage to follow the reference maximum power point voltage with the alleviation of slow transient response and disadvantages of chattering effects of variable-frequency hysteresis modulation sliding mode controller–maximum power point tracking. The perturbations caused by the uncertainties in climatic conditions and converter output bulk oscillations during grid integration are also mitigated. The features of the proposed photovoltaic–active power filter integration system are confirmed at different operating conditions through PSIM simulation software, and its performance is also compared with a conventional variable-frequency sliding mode-controlled maximum power point tracking. The obtained simulation and experimental results give good dynamic response under various operating conditions of environmental and local load conditions.

Fixed-Frequency Sliding-Mode Control Scheme Based on Current Control Manifold for Improved Dynamic Performance of Boost PFC Converter

This paper deals with the switching regulation of boost power factor correction (PFC) converter under large and quick load fluctuation to ensure tight output voltage regulation and unity PF (UPF) at line side. In this sense, the sliding-mode control (SMC) technique based on current-controlled manifold is proposed. Input current distortion is limited even during light loading condition. In addition, the dead-zone issue related to light load near to the crossover of input current is resolved in this paper. To execute the proposed SMC algorithm, equivalent control approach is used for the selection of sliding coefficients, ensuring the system stability. The control operation manipulates both inner SM current controller to frame input current and an outer PI controller to maintain desired regulated output voltage. For experimental validation, a 500-W, 390 V/dc boost PFC prototype, controlled by dSPACE 1104 signal processor is framed. The presented simulation and experimental results infer that the proposed converter controller offers UPF, tight output voltage regulation, and percentage total harmonic distortion standard even under fluctuating load behavior. In this paper, the performance of the proposed control scheme is experimentally verified with different load behaviors and external references, which explains the robustness and effectiveness of the proposed system.

Hyper‐plane sliding mode control of the DC–DC buck/boost converter in continuous and discontinuous conduction modes of operation

In this study, a new proportional–integral-type hyper-plane sliding mode controller has been designed for output voltage control of the DC–DC buck/boost converter for its continuous and discontinuous conduction modes of operating conditions. The proposed controller is robust and stable against parameters uncertainties, load disturbance and variations of the converter input voltage. In addition, it is capable of cancelling the non-minimum phase nature effect of the converter so that the designed controller does not need to know the inductor reference current. Moreover, the coefficients of the controller have been designed so that the steady-state error of the converter asymptotically converges to zero. The controller is designed based on fixed-frequency equivalent control approach. Using MATLAB/SIMULINK toolbox and digital signal processor (TMS320F2810) from Texas Instruments, some simulation and practical results are presented to verify the capability and effectiveness of the proposed control approach.

Second-Order Sliding Mode Control with PI Sliding Surface and Experimental Application to an Electromechanical Plant

In this article, a second-order sliding mode control (2-SMC) is proposed for second-order uncertain plants using equivalent control approach to improve performance of control systems. A Proportional+Integral (PI) sliding surface is defined for the sliding mode. The sliding mode control law is derived using direct Lyapunov stability approach and asymptotic stability is proved theoretically. The second-order plant parameters are experimentally determined using input-output measured data. Performance of the closed-loop system is analysed through an experimental application to an electromechanical plant to show feasibility and effectiveness of the proposed 2-SMC and factors involved in the design. Results of the experimental application are presented to make a quantitative comparison with the traditional (first-order) sliding mode control and PID control. It is demonstrated that the proposed 2-SMC system improves performance of the closed-loop system with better tracking specifications in the case of external disturbances, better behavior of the output and faster convergence of the sliding surface while maintaining the stability.

A nonlinear sliding surface to improve performance of a discrete-time input-delay system

A sliding mode controller is proposed for an uncertain input-delay system to enhance performance. A nonlinear sliding surface is proposed to achieve better transient response for general uncertain discrete SISO linear systems with input delay. Both matched and unmatched perturbations are considered and ultimate boundedness of motion is proved. The step tracking problem is analysed. The proposed surface increases the damping ratio of the transformed system (delay free) as the output moves nearer to the setpoint. To simplify the surface design, a linear matrix inequality based tuning procedure is proposed. The control law is designed based on an equivalent control approach which guarantees one step reaching. The scheme is able to achieve low overshoot and low settling time simultaneously which is not possible with a linear sliding surface. Simulation results verify the effectiveness of the proposed nonlinear surface over different linear surfaces.

Sliding mode control for time-varying delayed systems based on a reduced-order observer

In this paper, a stabilisation problem for a class of nonlinear systems is considered, where both the nonlinear term and the nonlinear uncertainty are mismatched and subject to time-varying delay. Under the assumption that the delay is known, a reduced-order observer is designed using an appropriate transformation. A sliding surface is proposed in an augmented space formed by the system outputs and the estimated states. The sliding mode dynamics are derived using an equivalent control approach, and the Lyapunov–Razumikhin approach is exploited to analyse the stability of the sliding motion. Then, a sliding mode control law is developed such that the system can be driven to the sliding surface in finite time. A simulation example shows the effectiveness of the proposed approach.

Second-order sliding mode control with experimental application

In this article, a second-order sliding mode control (2-SMC) is proposed for second-order uncertain plants using equivalent control approach to improve the performance of control systems. A Proportional + Integral + Derivative (PID) sliding surface is used for the sliding mode. The sliding mode control law is derived using direct Lyapunov stability approach and asymptotic stability is proved theoretically. The performance of the closed-loop system is analysed through an experimental application to an electromechanical plant to show the feasibility and effectiveness of the proposed second-order sliding mode control and factors involved in the design. The second-order plant parameters are experimentally determined using input–output measured data. The results of the experimental application are presented to make a quantitative comparison with the traditional (first-order) sliding mode control (SMC) and PID control. It is demonstrated that the proposed 2-SMC system improves the performance of the closed-loop system with better tracking specifications in the case of external disturbances, better behavior of the output and faster convergence of the sliding surface while maintaining the stability.

Hypofractionation Regimens for Stereotactic Radiotherapy for Large Brain Tumors

To investigate equivalent regimens for hypofractionated stereotactic radiotherapy (HSRT) for brain tumor treatment and to provide dose-escalation guidance to maximize the tumor control within the normal brain tolerance. The linear-quadratic model, including the effect of nonuniform dose distributions, was used to evaluate the HSRT regimens. The alpha/beta ratio was estimated using the Gammaknife stereotactic radiosurgery (GKSRS) and whole-brain radiotherapy experience for large brain tumors. The HSRT regimens were derived using two methods: (1) an equivalent tumor control approach, which matches the whole-brain radiotherapy experience for many fractions and merges it with the GKSRS data for few fractions; and (2) a normal-tissue tolerance approach, which takes advantages of the dose conformity and fractionation of HSRT to approach the maximal dose tolerance of the normal brain. A plausible alpha/beta ratio of 12 Gy for brain tumor and a volume parameter n of 0.23 for normal brain were derived from the GKSRS and whole-brain radiotherapy data. The HSRT prescription regimens for the isoeffect of tumor irradiation were calculated. The normal-brain equivalent uniform dose decreased as the number of fractions increased, because of the advantage of fractionation. The regimens for potential dose escalation of HSRT within the limits of normal-brain tolerance were derived. The designed hypofractionated regimens could be used as a preliminary guide for HSRT dose prescription for large brain tumors to mimic the GKSRS experience and for dose escalation trials. Clinical studies are necessary to further tune the model parameters and validate these regimens.

Indirect Sliding Mode Control of Power Converters Via Double Integral Sliding Surface

The steady-state regulation error in power converters that use the conventional hysteresis-modulation-based sliding mode controller can be suppressed through the incorporation of an additional integral term of the state variables into the controller. However, it is found that with the indirect type of sliding mode controller (derived based on the equivalent control approach), the same approach of integral sliding mode control is ineffective in alleviating the converter's steady-state error. Moreover, the error increases as the converter's switching frequency decreases. This paper presents an in-depth study of the phenomenon and offers a solution to the problem. Specifically, it is proposed that an additional double-integral term of the controlled variables to be adopted for constructing the sliding surface of indirect sliding mode controllers. Simulation and experimental results are provided for verification.

SELF-TUNING CONTROL BASED ON GENERALIZED MINIMUM VARIANCE CRITERION.

The stability of adaptive control systems has been studied extensively for minimum phase systems, mainly for model reference adaptive systems, but complete stability proof for non-minimum phase systems have not been given. In this paper, the stability of two types of self-tuning controllers for discrete time minimum and non-minimum phase plants is studied, namely: recursive estimation of the implicit self-tuning controller parameters based on generalized minimum variance criterion (REGMVC), and another based on generalized minimum variance criterion - β equivalent control approach (REGMVC-β). Stability of the algorithms are proved by the Lyapunov theory.

ON SLIDING MODE OBSERVERS FOR NON-LINEAR SYSTEMS UNDER EXTERNAL DISTURBANCES

The paper introduces the cascade principle of sliding mode observer design for non-linear systems under external disturbances. An equivalent control approach will be utilized for step-by-step reconstruction of the non-measured components of the state and external disturbances also.

Output feedback sliding mode control for non-minimum phase systems with non-linear disturbances

In this paper, robust stabilization for a class of systems with a non-linear disturbance is considered. The non-linear disturbance is mismatched and has a non-linear bound. The nominal system is allowed to be non-minimum phase. A dynamical compensator is designed to estimate the system state and a sliding surface, in the augmented space formed by the system output and the estimated state, is proposed. The stability of the corresponding sliding mode is analysed using the equivalent control approach. Based on the estimated state variables and system output, a variable structure control scheme is developed such that the system is driven to the sliding surface and maintained on it thereafter. Finally, a simulation for a nonminimum phase HIRM aircraft model is presented to illustrate the effectiveness of the results.

A discrete-time sliding mode controller and observer with computation time delay

Based on discrete-time sliding mode, a robust controller and an observer that consider computation time delay are presented. The computation time delay is assumed to be constant and smaller than the sampling time. To cancel out the effects of perturbation, the proposed controller uses the concept of Time Delay Control (TDC). In the design of the observer, the concept of the discrete-time equivalent control approach is adopted. Furthermore, the combined controller–observer system is investigated. The usefulness of the proposed controller and the observer is demonstrated through experiments on a direct drive motor.

On sliding mode observers via equivalent control approach

In this paper, sliding mode observer design principles based on the equivalent control approach are discussed for a linear time invariant system both in continuous and discrete time. For the continuous case, the observer is designed using a recursive procedure; however, the observer is eventually expressed as a replica of the original system with an additional auxiliary input with a certain nested structure. A direct discrete time counterpart of the sliding mode realization of a reduced order asymptotic observer using the discrete time equivalent control is also developed. Simulation of a linearized truck-trailer during a manoeuvre illustrates the approach. Results show the effectiveness and the finite time convergence characteristics of the proposed discrete and continuous time sliding mode observers.