This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in a MATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility.

The smart grid has become a cyber-physical system and the more cyber it becomes, the more prone it is to cyber-attacks. One of the most important cyber-attacks in smart grids is false data injection (FDI) into its measurement infrastructure. This attack could manipulate the control center in a way to execute wrong control actions on various generating units, causing system instabilities that could ultimately lead to power system blackouts. In this study, a novel false data detection and prevention paradigm was proposed for the measurement infrastructure in smart grids. Two techniques were devised to manage cyber-attacks, namely, the fixed dummy value model and the variable dummy value model. Limitations of the fixed dummy value model were identified and addressed in the variable dummy value model. Both methods were tested on an IEEE 14 bus system and it was shown through the results that an FDI attack that easily bypassed the bad data filter of the state estimator was successfully identified by the fixed dummy model. Second, attacks that were overlooked by the fixed dummy model were identified by the variable dummy method. In this way, the power system was protected from FDI attacks.

Purpose: This paper aims to propose a robust cascaded controller based on proportional-integral (PI) and continuous sliding mode control. Design/methodology/approach: Cascaded control structure is an attractive control scheme for DC-DC power converters. It has a two-loop structure where the outer loop contains PI controller and the inner loop uses sliding mode control (SMC). This structure thus combines the merits of both the control schemes. However, there are some issues that have prohibited its adoption in industry, the discontinuous nature of SMC which leads to variable switching frequency operation and is hard to realize practically. This paper attempts to overcome this issue by changing the discontinuous functionality of SMC to continuous by utilizing the concept of equivalent control. Findings: The robustness of the controller designed is verified by considering various cases, namely, ideal case with no uncertainties, sudden variation of input supply voltage, load resistance, reference voltage, circuit-parameters and for noise disturbance. The controller effectiveness is validated by simulating the DC-DC boost and Cuk converters in SimPowerSystems toolbox of MATLAB/Simulink. It is shown that the performance of the proposed controller is satisfactory, and both reference output voltage and inductor current are tracked with little or no sensitivity to disturbances. Originality/value: The results for various scenarios are interesting and show that the controller works quite satisfactorily for all the simulated uncertainties.