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A new custom power device (CPD) is introduced for real-time control of reactive power and improving the overall network voltage quality of smart grid (SG) at fundamental and harmonic frequencies, respectively. The idea is to take advantage of the online smart meter data transmitted from each bus to the SG central control to concurrently perform the static synchronous compensator and the active power line conditioner operations by optimal compensations of fundamental reactive power and harmonic currents at selected optimal buses. The proposed strategy involves two particle swarm optimization algorithms. The first algorithm is implemented for the worse operating condition to determine the optimal locations and sizes of CPDs while the second algorithm relies on smart meter information to continuously compute fundamental and harmonic reference currents for real-time operation and control of the allocated CPDs. The objective functions are cost minimizations associated with bus voltage regulations, network total harmonic distortions voltage and custom device sizing while the constraints include upper limits for CPD sizes, fundamental, and harmonic bus voltages. Detailed simulations are performed in MATLAB/Simulink to evaluate the performances of allocated CPDs in controlling the reactive power and voltage quality of a distorted 15-bus SG with six nonlinear loads according to the IEEE-519 standard.

Low frequency oscillations (LFOs) are load angle oscillations that have a frequency between 0.1-2.0 Hz. Power system stabilizers (PSSs) are very effective controllers in improvement of the damping of LFOs. PSSs are designed by linearized models of the power system. This paper presents a new model of the power system that has the advantages of the Single Machine Infinite Bus (SMIB) system and the multi machine power system. This model is named a single machine normal- bus (SMNB). The equations that describe the proposed model have been linearized and a lead PSS has been designed. Then, particle swarm optimization technique (PSO) is employed to search for optimum PSS parameters. To analysis performance of PSS that has been designed based on the proposed model, a few tests have been implemented. The results show that designed PSS has an excellent capability in enhancing extremely the dynamic stability of power systems and also maintain coordination between PSSs.

Some of the earliest power system stability problems included spontaneous power system oscillations at low frequencies. These Low-Frequency-Oscillations (LFOs) are related to the small-signal stability of a power system and are harmful to obtain the maximum power transfer. A contemporary solution to this problem is the addition of Power System Stabilizers (PSSs) to the automatic voltage regulators on the generators in the power system. In this paper, allocation of PSSs in an interconnected power system with inter-area modes has been determined by eigenvalue analysis, and PSSs for the allocated generators have been designed by a frequency response method. Furthermore, for designing PSSs by the frequency method, this paper proposed a new linear power system model which can consider both local and inter-area oscillations of the power network. Designed PSSs based on the proposed model improved damping performance of PSSs which have been designed by the Single-Machine-Infinite-Bus (SMIB) model. The stabilization performance of the designed PSSs (by the proposed approach and linear power system model) on the LFO modes have been verified in two multi-machine power system standard models (IEEE 9-bus and 14-bus).

Distributed generators are acquiring more attention in power systems because they can avoid distribution and transmission upgrade requirements and improve power quality issues. Islanding is one of the problems that arise with integrating these resources into the distribution system. In this article, a novel hybrid islanding detection technique is proposed which uses average rate of voltage change and capacitor bank tap switching. The proposed method is tested on a real system and different load characteristics with different dependence coefficients to voltage and frequency are studied. The power system is perturbed only when the method suspects that islanding has occurred. The proposed method could detect islanding conditions with very small power mismatches in them.

Solid-state fault current limiters (SSFCL) in power systems are alternative devices to limit prospective short circuit currents from reaching lower levels. Fault current limiters (FCL) can be classified into two categories: R-type (resistive) FCLs and L-type (inductive) FCLs. L-type FCL uses an inductor to limit fault level and is more efficient in suppressing voltage drop during a fault. In contrast, R-type FCL is constructed with a resistance and is more effective in consuming the acceleration energy of generators during a fault. Both functions enhance the transient stability of the power system. In the present paper, a novel SSFCL is proposed to enhance power system transient stability and power quality. The proposed SSFCL uses both functions of an L-type and R-type FCL. SSFCL consists of four diodes, one self-turn-off IGCT, a current-limiting by-pass inductor (L), and a variable resistance parallel with an inductor for improvement of power system stability and prevention of over-voltage across SSFCL. The main advantages of the proposed SSFCL are the simplicity of its structure and control, low steady-state impedance, fast response, and the existence of R-type and Ltype impedances during the fault, all of which improve power system stability and power quality. Simulations are accomplished in PSCAD/EMTDC.

The Hysteresis current control (HCC) is a popular modulation technique used in active power filter (APF) applications owing to its simplicity of implementation, fast current response and peak current limiting capability. Despite these advantages, it has a major disadvantage when applied to three-phase isolated neutral point (INP) systems: interphases dependency causes very high-switching frequencies. To overcome this problem, this paper presents a new space-vector hysteresis current control (SVHCC) modulation for APFs when applied to three-phase INP systems. The space-vector-based method allows for the efficient use of zero-voltage vectors and prevents high switching frequencies caused by phase interference. The approach comprises of initially performing two hysteresis bands around the error vector in the αβ stationary reference frame (SRF) and then selecting the next voltage vector based on the present location of the error vector to reduce the next error vector. The proposed approach is verified through detailed simulations using MATLAB software.