This study presents a new wide-area voltage stability monitoring method using synchronised phasor measurements. The salient features of the proposed index are the following: (i) It ensures constancy, which is the ability to maintain the same scale even if the system changes. (ii) It is pseudo-linear with respect to the power system stability level, which enhances intuitiveness for real-time operation. Accordingly, stability can be uniformly compared in various situations, and thus, the index can be used as a solid criterion or threshold point for system operation. A verification study of the proposed index with regard to constancy is carried out using Korean power system operation data. Furthermore, an implementation of the proposed method for the Korean wide-area monitoring system is presented, and it is demonstrated that the proposed index detects event more clearly than previous stability index through an actual event measured using phasor measurement units.

A novel quasi-oppositional-based salp swarm algorithm (QSSA) is used to obtain the optimal values of controllers for automatic generation control of the two-area, assorted source of the generation-based power system. Thermal, hydro, and gas generating units are considered in the power system. Optimal values of proportional–integral–derivative (PID) controllers obtained using SSA and QSSA are compared with that of PID controllers based on differential evolution, teaching learning-based optimisation, and imperialist competitive algorithm. Observing the superiority with a QSSA-based PID controller, the study is protracted to obtain the optimal values of two-degree-of-freedom conventional PID (2DOF-PID) and 2DOF fractional order PID (2DOF-FOPID) controller with SSA and QSSA techniques. It is evidenced that QSSA outperforms SSA and also the QSSA-based 2DOF-FOPID controller establishes a better dynamic response than other controllers. 2DOF-FOPID controller is also employed for the system with generation rate constraint (GRC). The complete analysis is carried out by applying a step load disturbance of 1 p.u. in area-1. Robustness of the controller is verified by varying the systems' parameters and a randomly varying loading pattern in both areas with and without GRC. In both cases, the proposed QSSA-based 2DOF-FOPID controller is found firmly robust.

This study investigates the impact of embedded voltage source converter-based high voltage direct current (VSC-HVDC) links on AC grids transient stability. Firstly, using transient energy functions, it is demonstrated that VSC-HVDC links controlled to track constant power references, do not inherently improve transient stability of the surrounding AC grid as an AC line naturally does. Then, a control law using the feedback linearisation technique on a simple but representative power system is derived. The control law highlights and combines the three main actions the VSC-HVDC link can offer to enhance rotor angle stability: fast power reallocation, injection of synchronising power and injection of damping power. The control law is implemented and validated in EMT simulation. It is then shown that an HVDC link can assure the synchronisation of different AC areas even if no AC transmission lines interconnect them. Through another case study, it is shown how the HVDC link can help to share dynamic frequency reserves to not jeopardise the stability of the system. The last example investigates the effect of a DC fault on AC transient stability and how the control can help improving the system response.

In this study, power quality (PQ) improvement has been addressed, in the form of total harmonic distortion (THD) minimisation, as well as, voltage regulation using two cascaded schemes. The first scheme is the optimised triple action controller (TAC)-based pulse width modulated voltage source inverter. TAC consists of a proportional resonant controller, selective harmonic compensator, and a new added current-assisted feed forward controller. The second scheme is the optimised cascaded dual-level control of a standalone microgrid. Cascaded level control consists of droop, secondary, and synchronisation control loops. The two approaches have been optimised for best parameter selection out of the possible solution space using a particle swarm optimisation algorithm to satisfy the study objectives. The optimisation objectives/constraints were to minimise THD and minimise overshoot/undershoot, rise time, and steady-state error for voltage compensation under two disturbance scenarios, sudden load change, and voltage flicker injection as a power frequency disturbance. These research results have been compared to other existing simulation and experimental work. The results proved to be better in output voltage, frequency, response time, and THD. Furthermore, the proposed schemes ensure power factor improvement, high efficiency, overall system PQ, and reliability at various load conditions.

This study presents a single stage grid-interfaced solar photovoltaic (SPV) system using a multifunctional complex coefficient reduced ordered generalised integrator (CC-ROGI) based frequency-locked loop (FLL) control. The main contributions of this study, include (i) the extrication of fundamental active components from load currents using CC-ROGI-FLLbased control to generate the reference grid currents for voltage source converter (VSC) switching, (ii) VSC works as a distribution static compensator, which performs multi-functions like harmonics mitigation, reactive power compensation, unity power factor operation and grid currents balancing, (iii) this CC-ROGI-FLL also extricates the fundamental grid voltages component even under grid voltage harmonic distortion and grid voltages unbalancing. Moreover, SPV power feed-forward component is assimilated in this control to reduce the oscillations in grid currents under variable irradiance. Simulated and experimental results show satisfactory behaviour of the system at different conditions like load unbalancing, variable solar irradiance and abnormal grid conditions. The comparative performance of CC-ROGI-FLL control with other FLL and phaselocked loop controls are shown in this study. This CC-ROGI-FLL control has manifested a good steady state performance and dynamic response. The total harmonic distortions of grid currents are found well within the limits of the IEEE-519 standard, even under abnormal grid conditions.