This paper presents a new control strategy that combines classical control and an optimization scheme to regulate the output voltage of the bidirectional converter under the presence of matched and mismatched disturbances. In detail, a control-oriented modeling method is presented first to capture the system dynamics in a common canonical form, allowing different disturbances to be considered. To estimate and compensate for unknown disturbances, an extended state observer (ESO)-based continuous sliding mode control is then proposed, which can guarantee high tracking precision, fast disturbance rejection, and chattering reduction. Next, an extremum seeking (ES)-based adaptive scheme is introduced to ensure system robustness as well as optimal control effort under different working scenarios. Finally, comparative simulations with classical proportional-integral-derivative (PID) control and constant switching gains are conducted to verify the effectiveness of the proposed adaptive control methodology through three case studies of load resistance variations, buck/boost mode switching, and input voltage variation.

https://www.mdpi.com/1424-8220/23/1/457/pdf?version=1672970406

Robust Adaptive Control Strategy for a Bidirectional DC-DC Converter Based on Extremum Seeking and Sliding Mode Control

In response to the issue of system oscillations in direct current (DC) microgrid systems with constant power loads (CPL), this paper proposes a non-singular terminal sliding-mode control (NTSMC) strategy based on the improved salp swarm algorithm (ISSA). Firstly, the state-feedback exact linearization technique is employed to establish a linearized model of the converter system. Then, the NTSMC based on a composite sliding-mode surface is designed to achieve rapid convergence and effectively weaken the chattering issue in traditional sliding-mode control, ensuring a constant power supply to the load. The parameters of the proposed NTSMC are optimized using the ISSA, which introduces an intelligent NTSMC. Finally, a MATLAB/Simulink simulation model is established. The simulation results show that the ISSA-based composite sliding-mode surface NTSMC system designed for DC microgrid systems with CPL exhibits high robustness and guarantees ideal steady-state characteristics and dynamic responses when input voltage fluctuations and load disturbances occur.

/pdf/intelligent-issa-based-non-singular-terminal-sliding-mode-3ca9umng.pdf

Intelligent ISSA-Based Non-Singular Terminal Sliding-Mode Control of DC–DC Boost Converter Feeding a Constant Power Load System

This paper presents the design and real-time implementation of a composite controller consisting of a state-feedback control law and high-gain observer for grid-tied inverter with LCL filter. The state-feedback controller is designed in the $dq$ reference frame to stabilize the closed-loop system. High-gain observer serves as a disturbance observer to estimate a fictitious variable, representing the effect of model uncertainties and unknown disturbances, which is then canceled by the state-feedback controller. Thus, asymptotic regulation can be guaranteed under the composite controller even in the presence of parametric uncertainties and unknown inputs. High-gain observer has a rate of convergence that is dependent on its gain which is required to be large enough to ensure fast disturbance estimation, and then nominal performance recovery. However, high observer gain can lead to poor steady-state performances due to the effect of measurement noise. This concern is overcome in this work by using an existing adaptive technique to adjust the observer gain on-line. Moreover, the resulting high-gain observer is further simplified to provide a less-complex estimator and to show its integral action property. The performance of the composite controller was experimentally tested. The obtained results demonstrated the ability of the proposed controller to meet the nominal performance specifications while reducing the effect of measurement noise in steady-state.

Adaptive High-Gain Observer-Based Control for Grid-Tied LCL Filter Systems

This paper proposes a static anti-windup compensator (AWC) design methodology for the locally Lipschitz nonlinear systems, containing time-varying interval delays in input and output of the system in the presence of actuator saturation. Static AWC design is proposed for the systems by considering a delay-range-dependent methodology to consider less conservative delay bounds. The approach has been developed by utilizing an improved Lyapunov-Krasovskii functional, locally Lipschitz nonlinearity property, delay-interval, delay derivative upper bound, local sector condition, L2 gain reduction from exogenous input to exogenous output, improved Wirtinger inequality, additive time-varying delays, and convex optimization algorithms to obtain convex conditions for AWC gain calculations. In contrast to the existing results, the present work considers both input and output delays for the AWC design (along with their combined additive effect) and deals with a more generic locally Lipschitz class of nonlinear systems. The effectiveness of the proposed methodology is demonstrated via simulations for a nonlinear DC servo motor system, possessing multiple time-delays, dynamic nonlinearity and actuator constraints.

/pdf/static-anti-windup-compensator-design-for-locally-lipschitz-tlpyauoi.pdf

Static anti-windup compensator design for locally Lipschitz systems under input and output delays

A DC-DC converter produces constant output voltage in the face of varying supply voltage, load current change, and circuit element variation. To achieve tight output voltage regulation in the presence of various disturbances, DC-DC converters incorporate a control strategy to regulate power flow and power level. In recent times, several control strategies have been investigated for regulating the action of DC-DC converters, ranging from the conventional frequency domain to time domain design approaches. However, not enough attention is given to the performance of the state feedback controller, especially during rapid load current change in dc-dc converter. In this paper, a full order state-feedback controller was designed, and the performance was investigated for rapid load current change. A state feedback controller was first designed in this work, and then the integrator is introduced to eliminate the inherent steady-state error for improved system robustness to disturbance rejection. The state feedback controller performance was evaluated by subjecting the converter to various step load current changes in which the controller rejected the disturbance faster when compared with the PID controller used as a base controller. The fast transient response will allow the DC-DC converter to accept wider current change from rapidly changing loads and achieve improved output voltage regulation.

Investigation of Full-Order State Output Feedback Controller on DC-DC Converter Rapid Load Current Change

The nonminimum-phase property of the dc–dc boost converter can create difficulties in designing a stable, robust, and fast control for the output voltage. In this article, these difficulties are reduced by modifying the state model of the boost converter in such a way that it behaves like a minimum-phase system. More specifically, the control input entering the state equation for the output voltage is treated as an unknown disturbance to make the relative degree of the system equal the system’s order. As a result, the modified model does not exhibit zero dynamics, so that it can be treated as a minimum-phase system for the control design. The modified model is, then, used to derive a dynamic compensator for the output voltage regulation. More explicitly, the dynamic compensator is designed based on combining linearizing feedback control with a disturbance observer. The latter is employed to compensate for model uncertainties and unknown load with a view to ensure asymptotic regulation under the composite controller. The asymptotic regulation is achieved due to the integral action property characterizing the disturbance observer. More interestingly, after simple algebraic manipulation, it turns out that the composite controller reduces to a dynamic state feedback control plus an antiwindup scheme to mitigate the effect of control saturation during transients. The performance of the proposed controller is verified by experimental tests. The experimental results demonstrate the ability of the proposed controller to achieve good transient and steady-state performances.

Disturbance-Observer-Based Feedback Linearization Control for Stabilization and Accurate Voltage Tracking of a DC–DC Boost Converter

This paper presents the design and real-time implementation of a composite controller consisting of a state-feedback control law and high-gain observer for LCL filter system in grid-tied applications. The main function of the feedback control law, designed in the $dq$ rotating reference frame, is to add a damping effect to the closed-loop system with a view to cancel the effect of the resonance frequency inherent in LCL filter system. High-gain observer is added to the feedback controller to achieve asymptotic regulation and disturbance rejection in the presence of model uncertainties and unknown disturbances. Specifically, high-gain observer is considered as a disturbance observer to compensate for the effect of parametric uncertainties and unknown inputs. High-gain observer has a rate of convergence that is dependent on its gain, which is required to be large enough to ensure fast disturbance estimation. However, high observer gain can lead to poor steady-state performances due to the effect of measurement noise. This concern is overcome in this work by using an existing adaptive technique to adjust the observer gain on-line. Moreover, the resulting high-gain observer is further simplified to provide a less-complex estimator and to show its integral action property. The performance of the composite controller was experimentally tested. The obtained results demonstrated the ability of the proposed controller to meet the control objectives with a reduced effect of measurement noise.

Robust Full Linear State-Feedback Controller for Grid-Tied LCL Filter Systems Using Adaptive High-Gain Observer

This paper presents a disturbance observer-based control (DOBC) for stand-alone inverters to produce sinusoidal voltages. The controller is specifically designed to regulate the output voltage of the inverter to follow a desired sinusoidal voltage reference. The disturbance observer is employed to ensure accurate tracking of the voltage reference by compensating for model uncertainties and unknown inputs. The combination of a linearizing feedback control (LFC) with a disturbance observer (DO) makes it possible to perform dual functions by providing improved disturbance rejection during transients and attaining zero steady-state error thanks to the integral action property of the disturbance observer. The key feature of the proposed controller is that it is designed in the dq reference frame, but it is implemented in stationary αβ coordinates. The performance of the above controller during load variations is verified via simulation tests. The test results have demonstrated excellent disturbance attenuation to achieve good transient response during balanced and unbalanced load variations.

Disturbance Observer-Based Feedback Linearization Control for Stand-Alone Inverters

In this paper, a robust dynamic compensator together with anti-windup scheme for a grid tied inverter with L filter is proposed to provide satisfactory tracking performance of the reference signal under control input saturation. The control implementation is performed in the αβ reference frame to make the systems output matches a sinusoidal reference signal with zero tracking error. The sinusoidal current references are calculated using the active power command, reactive power command, and sequence voltages to deal with both balanced and unbalanced grid voltages. The dynamic compensator has the property of a resonant action in that it ensures accurate tracking of sinusoidal references in the presence of sinusoidal disturbances with known frequency. With the resonant behavior of the feedback controller, considerable overshoot and settling time may occur in the transient response, particularly during control saturation. To compensate for the effect of control input saturation, the dynamic compensator was modified to include an anti-windup compensator. The role of the anti-windup scheme is to improve the quality of the transient behavior during control input saturation. Simulation tests were used to verify the suggested controller performance. The proposed composite controller demonstrated excellent tracking performance with a graceful degradation during control saturation under both balanced and unbalanced grid voltages.

Amulya Viswambharan

Papers

Disturbance-Observer-Based Feedback Linearization Control for Stabilization and Accurate Voltage Tracking of a DC–DC Boost Converter

Robust Full Linear State-Feedback Controller for Grid-Tied LCL Filter Systems Using Adaptive High-Gain Observer

Adaptive High-Gain Observer-Based Control for Grid-Tied LCL Filter Systems

Disturbance Observer-Based Feedback Linearization Control for Stand-Alone Inverters

A Robust Dynamic Compensator with Anti-windup Scheme for Grid-Interlinked Photovoltaic Inverter under Unbalanced Grid Voltages