Offset-free feedback linearisation control of a three-phase grid-connected photovoltaic system

In this study, a state feedback control law is combined with a disturbance observer to enhance disturbance rejection capability of a grid-connected photovoltaic (PV) inverter. The control law is based on input-output feedback linearisation technique, while the existing disturbance observer is simplified and adopted for the system under investigation. The resulting control law has a proportional-integral (PI)/almost PI-derivative-like structure, which is convenient for real-time implementation. The objective of the proposed approach is to improve the DC-bus voltage regulation, while at the same time control the power exchange between the PV system and the grid. The stability of the closed-loop system under the composite controller is guaranteed by simple design parameters. Both simulation and experimental results show that the proposed method has significant abilities to initiate fast current control and accurate adjustment of the DC-bus voltage under model uncertainty and external disturbance

Robust decentralized voltage and frequency control of generators in islanded microgrids using μ-synthesis

© 2016 IEEE. In this paper, a robust decentralized controller is designed for automatic voltage regulator (AVR) and load frequency control (LFC) systems of a generator in an islanded microgrid with multiple distributed generation systems. This control strategy can be readily applied to an islanded microgrid which consists of renewable distributed generation and energy storage systems. The control strategy proposed in this paper includes multiple local droop controllers, as well as robust decentralized controller that are designed and optimized independently by using the μ-synthesis technique. These controllers account for the dynamic coupling among the areas of the islanded microgrid without any communication links required among the local controllers. Moreover, these controllers are designed to be robust to the variations of different parameters of the microgrid, and hence improve the voltage and frequency control performance significantly. Simulation results of a small microgrid with a generator and a renewable energy resource confirm the effectiveness of the controller design approach proposed in this paper

Robust load frequency control in islanded microgrid systems using μ-synthesis and D-K iteration

© 2016 IEEE. In this paper, a robust controller is designed for the load frequency control (LFC) system in an islanded microgrid with multiple synchronous generation systems. This control strategy can be readily applied to an islanded microgrid which consists of renewable distributed generation and energy storage systems. The robust controller proposed in this paper includes multiple local controllers that are designed and optimized independently by using the μ-synthesis technique and D-K iteration algorithm. This controller accounts for the dynamic coupling among the areas of the microgrid without any communication links required among the local controllers. Moreover, the controller is designed to be robust to the variations of different parameters of the microgrid, and hence improves the frequency control performance significantly. Simulation results of a small islanded microgrid with three generators confirm the effectiveness of the controller design approach proposed in this paper

An optimization approach to design decentralized load frequency controllers for generators in islanded microgrids

© 2016 IEEE. In this paper, an optimal decentralized controller is designed for the load frequency control of a microgrid with multiple synchronous generation systems and renewable energy sources in the islanded mode of operation. The decentralized controller includes multiple proportional-integral (PI) controllers designed and optimized simultaneously by using a classical descent-direction Quasi-Newton based optimization technique. The optimal decentralized PI controller accounts for the dynamic coupling among the areas of the microgrid without any communication links required among the PI controllers, and hence improves the frequency control performance as compared to a set of optimal linear-quadratic Gaussian (LQG) integral controllers of eighth order which are designed independently. Simulation results confirm the effectiveness of the proposed decentralized control approach

Robust inverter control design in islanded microgrids using μ-synthesis

© 2016 IEEE. In this paper, a robust controller is designed to control the output voltage of an inverter with an LC type output filter in an islanded microgrid. The proposed controller includes a local droop controller, as well as a robust controller that is designed based on the μ-synthesis technique. The performance of the designed controller is proven to be robust to the uncertainties which include the time delay and parameter changes during the operation of the inverter, while the resonant oscillations are properly damped to meet the standard requirements. The proposed controller only relies on output feedback which alleviates the need for extra sensors to measure the states of the system. Simulation are conducted to verify the robust performance of the designed controller in the presence of parameter uncertainties and time delay

Control design in μ-synthesis framework for grid-connected inverters with higher order filters

© 2016 IEEE. In this paper, a robust controller is designed based on μ-synthesis method for grid-connected inverters. The performance of the controller is made robust against realistic uncertainties including the time delay and parameter changes, while the resonant oscillations are actively damped. The designed controller only relies on output feedback eliminating the need for extra feedback sensors that are normally used in full or partial state feedback systems. Simulation and experimental results confirm the satisfactory performance and robustness of the designed controller in both cases of a nominal system and a system with parameter variations

Robust h∞ DC link control design for high-power density converters with high-order filter in PV systems

© 2017 IEEE. This paper proposes a DC link controller based on H∞ method for robust and reliable operation of a single-phase grid-connected inverter with an LCL-filter in photovoltaic (PV) applications. The H∞ DC link controller minimizes the bus voltage fluctuations caused by the power variations of PV system. Also, the controller ensures system robustness against such power variations, which conventional controllers fail to guarantee. Furthermore, the controller improves the quality of the injected current into the grid as the reference of output current is generated by the proposed DC bus voltage controller. Simulation results and experimental results prove the superior performance and robustness of the proposed controller. Index Terms-High-power density converters, DC link control, robust control, H∞ method, distributed energy, PV application