With Measurements of grid voltage and current are essential for the optimal operation of the grid protection and control (P&C) systems. Grid parameters vary through time during the faults and especially in the converter interfaced resources (CIRs) rich power grid, and thus accurate estimation is critical to avoid the mis-operation of the P&C systems. In this paper, a moving horizon estimation (MHE) as an observer is devised and applied to estimate the grid line parameters and grid voltages for protection enhancement. Due to the proprietary and confidentiality of CIRs, the proposed approach uses the black-box model to represent their dynamics. Leveraging the easily accessible measurements of output current from the black-box model of CIR and voltage at the point of common coupling, the proposed method estimates the grid impedance and grid voltage during normal and faulty operating conditions. The performance shows that the optimization-based observer was able to closely observe the accurate states and parameters, which can be utilized by the P&C systems.

A fuzzy logic based online energy management system (FLEMS) is designed in this paper to achieve the optimal electricity cost in a residential Microgrid (MG). The proposed FLEMS is combined by a local energy price model (LEPM) and a fuzzy-logic strategy. The LEPM will preprocess the sampling data to estimate the electricity market and local MG status. The fuzzy-logic mimics the artificial intelligent assessment to economic issues and make decision for the charging and discharging operation for energy storage system (ESS). In the FLEMS, not only electricity price and supply-demand balance, but also ESS state of charge are considered for the efficient and stable operations. The proposed method does not relay on the accurate prediction of renewable energy source and local loads. Historical experience of the system is involved by the LEPM and guides the ESS operation in the fuzzy-logic. A real-world data based household-level residential MG model is established to validate the performance of the FLEMS. A hourly-resolution-Particle swarm optimization (PSO) with perfect day-ahead prediction is implemented as the baseline to verify the superiority of the proposed method.

Although the current sharing control of dc microgrids has been widely studied, the high communication bandwidth and global communication network structure information demands hander the renewable energy consumption. Thus, this article proposes a fully distributed dynamic edge-event-triggered current sharing control strategy for multibus dc microgrids with power coupling. First, the system model with power coupling is built, which is further switched to the linear heterogeneous multiagent systems with unknown disturbance. It is an indispensable preprocessing for controller design. Furthermore, the fully distributed current sharing control strategy is proposed through adaptive coupling weights. Note that the global communication network structure information demand is eliminated. Moreover, the fully distributed dynamic edge-event-triggered mechanism is proposed to reduce communication bandwidth. Compared with the previous dynamic event-triggered mechanisms applied into dc microgrids, the continuous communication between neighboring agents is avoided, and controller updating frequency is reduced. Finally, the simulation and experimental results verify the proposed control performance.

Although the cyber-physical system stability is widely studied, scholars focus more on system stability with communication time delay. Therein, grid-connected inverters with the digital control system are regarded as one simplest and typical cyber-physical system. Meanwhile, the switching/sampling frequency of the inverter is always selected as low as possible from an efficiency viewpoint, resulting in unavoidable delay time. This delay time is apt to cause the system instability, which is more prone to severity under weak grid. To this end, this paper provides a minimum switching/sampling frequency for grid-connected inverters. Firstly, the system impedance model with equivalent delay time is constructed, which is based on padé approximate approach. This equivalent delay time consists of three parts, i.e., sampling delay time in cyber/physical level, calculation delay time in cyber level and pulsewidth modulation delay time in physical level, which reflects the cyber-physical interaction impact. Furthermore, the stability forbidden criterion is applied to make the switching/sampling frequency solving process become Hurwitz matrix identification problem through space mappings. Based on these space mappings, an adaptive step search approach is adopted to obtain the minimum switching/sampling frequency. Finally, the proposed approach can well evaluate the system stability under different frequencies through simulation and experiment.

A coordinated control strategy of PV inverters is proposed to keep voltages within the specified limits in distribution grids. The proposed method consists of a local volt-VAr control and a centra coordinating control to manage reactive power outputs of PV inverters efficiently. The local control embedded in the inverter controller is operated based on the local measurements in order to improve the voltage quality. The central coordinating control collects measurements throughout the grid to control the voltages inside limits and coordinate the PV inverters' contributions. In the long term, the aim is then to obtain an optimum distribution of their contributions to voltage quality between the different PV inverters. To this purpose, volt-VAr set-points are sent from a central coordinating control to the local one of PV inverters through communication, forcing them to change their reactive power output based on the local measurement voltage and thereby improving the voltage quality. The effectiveness of the proposed method is demonstrated on an actual Danish grid.

In this article, a novel passivity-based control strategy is proposed for the exponentially stable tracking controller design of static synchronous compensator (STATCOM) system, which is a single input and single output. The STATCOM is not an input-affine system but a special port-controlled Hamiltonian system form. Hence, it is regularized by using a dynamic extension algorithm so that the proposed tracking control strategy is designed in an input-output linearization framework with a bounded solution to the driven zero dynamics equation. The proposed control strategy is proposed with consideration of the performance and stability of the input-output linearized dynamics. Simulation results show that the proposed control strategy improves the transient performance of the system compared to the previous results even in the lightly damped operating range.

In this paper, an improved grid voltage modulated control (GVM) with power compensation is proposed for grid-connected voltage inverters when the grid voltage is unbalanced. The objective of the proposed control is to remove the power ripple and to improve current quality. Three power compensation objectives are selected to eliminate the negative sequence components of currents. The modified GVM method is designed to obtain two separate second-order systems for not only the fast convergence rate of the instantaneous active and reactive powers but also the robust performance. In addition, this method converts the system into a linear invariant system though designing a new voltage input. Simulation results are presented to verify the correctness and validity of the proposed control strategy and power compensation method.

This paper presents a new direct active and reactive power control (DPC) controller scheme for a three-phase grid connected voltage source inverter (VSI) based on passivity viewpoint. The proposed method is designed in the framework of port-controlled Hamiltonian system. The proposed method is made up of two parts, one thing is a feedfoward part and the other is a feedback part. The feedforward part is calculated from the model dynamics of VSI. The feedback part is designed to compensate for system uncertainty. The proposed method is verified with simulation and experiment. The simulation uses MATLAB/Simulink and PLECS, and the experiment uses hardware in the loop (HIL) with TI TMS320F28335 DSP. The simulation and experiment results compared with those using direct power control-sliding mode control (DPC-SMC) for the grid connected VSI. The proposed method gives less total harmonic distortions, faster transient response.