Stochastic Convex Optimization for Optimal Power Factor Correction in Microgrids with Photovoltaic Generation

Loss reduction and loadability enhancement with DG: A dual-index analytical approach

A Quasi-Oppositional-Chaotic Symbiotic Organisms Search algorithm for optimal allocation of DG in radial distribution networks

Power factor correction has always been challenging task. Most of electrical energy is wasted due to leading and lagging power factor. Thyristor switch modules are widely used in the rolling mills where more fluctuating load is available. The thyristor switch module with the reactor and capacitor is usedfor the compensating the reactive power in electrical power system. Automatic power factor correctionunit is required to keep unity power factor and optimize current consumption. Harmonics is reduced by connecting detuned reactor/inductor in series with capacitor and thyristor switched module. This paper shows design and hardware implementation of thyristorised automatic power factor correction unit for three phase circuit in an industry. The unit is flexible to maintain nearly unity power factor. The outcome is confirmed and acquired that the recommended circuit is perfect to produce improved output.

Grid support functionalities from advanced PV inverters are increasingly being utilized to help regulate grid conditions and enable high PV penetration levels. To ensure a high degree of reliability, it is paramount that protective devices respond properly to a variety of fault conditions. However, while the fault response of PV inverters operating at unity power factor has been well documented, less work has been done to characterize the fault contributions and impacts of advanced inverters with grid support enabled under conditions like voltage sags and phase angle jumps. To address this knowledge gap, this paper presents experimental results of a three-phase photovoltaic inverter's response during and after a fault to investigate how PV systems behave under fault conditions when operating with and without a grid support functionality (autonomous Volt-Var) enabled. Simulations were then conducted to quantify the potential impact of the experimental findings on protection systems. It was observed that fault current magnitudes across several protective devices were impacted by non-unity power factor operating conditions, suggesting that protection settings may need to be studied and updated whenever grid support functions are enabled or modified.

The paper presents a single-stage high-power-factor electronic ballast for metal halide lamps. The proposed ballast integrates a buck-boost converter, a buck converter and a full-bridge inverter into a single power conversion circuit. The buck-boost converter served as a power-factor corrector (PFC) is designed to operate at discontinuous conduction mode (DCM) to achieve nearly a unity power factor at the input line. By adjusting the duty-ratio of the active switches of the PFC, the lamp power is remained at rated value for universal input voltage ranged from 90 V rms to 264 V rms . The four active switches of the full-bridge inverter, an inductor and a capacitor form a bidirectional buck converter which supplies a low frequency square-wave current for the lamp at to avoid the lamp from happing acoustic resonance. The circuit operation is analyzed in detail to derive the design equations. A prototype electronic ballast for a 70 W metal halide lamp is built and tested. Experimental measurements are provided to verify that the proposed ballast has the merits of a nearly unity input power factor, high circuit efficiency and the metal halide lamp is free of acoustic resonance.

Nowadays, the proliferation of photovoltaic (PV) generators and plug-in hybrid electric vehicles (PHEVs) into power distribution systems highly escalates. The variable PV power and the abrupt power charging of PHEVs result in system power and voltage fluctuations. This paper presents the new application of the superconducting coil (SC), which is connected between the dc link of PV generators to solve this problem. Using the dc-to-dc converter as an interfaced circuit, the SC can share the inverters with the PV generators. In addition, the PV generators with the common SC are able to provide the smooth power output and regulate the system voltage. The PV inverters and the dc-to-dc converter are controlled by the proportional-integral (PI) controllers. The optimization of the PI parameters and SC inductance is performed, so that the power and voltage fluctuations are minimized. Simulation results indicate that the PV generators with the common SC, which has a lower SC inductance, provide the same smoothing effect on the PV power fluctuation as the superconducting magnetic energy storage (SMES) installed at the PV terminal. In addition, they give the superior voltage regulation effect to the SMES.

A number of studies have shown that better DG PV integration impacts, on the network are obtained when the DG PV are operated at lower power factors. However, at lower power factors, losses tend to increase, whilst voltage improvement is rather realized in the sub - transmission network. In this study, with the help of the CYME distribution software, the optimal impacts of varying the DG PV power factors on the ECG 33 kV sub - transmission network voltages and losses, are studied. The study revealed that as power factors at which DG PV is operated are reduced, bus voltages generally increase. However, losses rather tend to follow a U-shape trajectory. The minimum loss recorded in the sub-transmission network was 1.032 %, representing a 6.522 % reduction over the base case scenario value of 1.104 %. The corresponding optimal power factor of the DG PV was found to be 0.97.

Power factor and harmonics are primary factors in electrical distribution network. Harmonics are generated by the non-linear and irregular loads at end users. High harmonics in devices draws the large amount of current which results in poor power factor. Hysteresis control technique is one of the techniques in power factor converter topologies. Switching losses, low power factor and high harmonic distortion factors have been observed in present topology. To overcome these problems, synchronous PFC boost converter with controller has been proposed. This control scheme improves power factor (PF) and minimizes current harmonics. Advantages of proposed control technique includes low switching losses, low harmonic distortion, nearly unity power factor and bidirectional power flow. This conceptually built low cost synchronous PFC boost converter with controller has been tested and demonstrated for its functionality.

This paper gives a new insight into the concept of load compensation under distorted voltages. Achieving both unity power factor (UPF) and perfect compensation of current harmonics are not possible where competition will arise between these two important factors. Through evaluating the present control strategies, a generalized, optimal, and flexible control strategy (OFC) for harmonic compensation of utility lines is proposed. The proposed control strategy, which provides a unified and highly flexible compensation framework has the ability of programming for perfect current harmonics compensation, or (UPF) accomplishment, or other newly defined objectives such as maximizing the power-factor subject to some adjustable constraints on the level of current harmonics and unbalancing via an on-line optimization algorithm. The strategy can fulfill the IEEE-519 standards requirements, while guaranteeing the best achievable power factor and optimum required rating for the compensator. Theoretical concepts and practical features of the proposed control strategy have been shown through extensive simulation studies using MATLAB/SIMULINK programs.

This paper is mainly focused on the stability-related issues of a grid-tied interlinking converter system. First, hybrid AC/DC admittance characteristics of an interlinking converter operating under unity and non-unity power factors are analyzed separately. Then, by using the hybrid AC/DC admittance and determinant-based General Nyquist Criterion (GNC), the stability assessment, instability root cause identification, and instability mitigation of a grid-tied interlinking converter system are studied. In addition, decoupled mitigation of the AC- and DC-side instabilities are discussed based on the hybrid AC/DC admittance characteristics. The study results show that when an interlinking converter operates under unity power factor, the stabilities of the AC and DC sides are decoupled and can be regulated independently. To be more specific, the DC-side stability is subjected to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$d$</tex-math></inline-formula> -axis admittance, DC admittance, and their coupling admittances while the AC-side stability is dominated by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> -axis admittance. According to the hybrid AC/DC admittance characteristics, this paper further reveals that the DC-side stability is determined by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$d$</tex-math></inline-formula> -axis controllers. In contrast, the AC-side stability is governed by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> -axis controllers and the phase-locked loop (PLL). Finally, the analysis presented in this paper is verified based on frequency- and time-domain simulations in the Matlab/Simulink environment.

This paper presents the conception and analysis of a switch-mode power supply (SMPS) with desirable characteristics of high-frequency isolation, high input power factor, low harmonic distortion, and high efficiency. Nearly unity input power factor can be obtained by using an interleaved boost converter associated with a nondissipative snubber, as high efficiency of the ac–dc front-end stage results. Additionally, a soft-switching full-bridge topology performs the dc–dc conversion, providing isolation to the SMPS by using a high-frequency transformer. By cascading both stages, the aforementioned characteristics are achieved. Theoretical background on each one of the converters is presented, and experimental results obtained from a laboratory prototype are presented and discussed in order to validate the proposal. In addition, the evaluation tests demonstrate the operation with nearly unity power factor, high efficiency, and good dynamic response over a wide load range.

Single-phase active impedance hybrid active power filter is design to mitigate harmonic and reactive caused by the ever-increasing nonlinear loads. Nonlinear loads have been increased in residential and commercial as well as industrial sectors. Single-phase nonlinear loads contribute a harmonics and low power factor for the power systems. Single-phase active impedance hybrid active power filter was investigated to actively adjust multiple active short circuits. The dominant load current harmonics are compensated due to its multiple short effects over the single-tuned LC filter. At the same time, the conservative power theory (CPT) base reactive current extraction method was applied to actively regulate the reactive power. The amount of the fundamental filter reactive current obtained from CPT determines the reactive power compensation. The results were analyzed and presented in collaboration with the MATLAB/Simulink environment and TMS320F28335 board. The active impedance and CPT based control achieved a harmonic compensation (from 65.96% to 3.20%) and power factor correction from 0.85 to 0.95. Therefore, the active impedance hybrid active power filter can be taken as a good candidate for harmonic and reactive compensation with extending the conventional hybrid active power filter (HAPF) into multiple active tuned filters. It has potential practical benefit to avoid regular field retuning the passive filter in the industry. Moreover, it can also apply for PQ compensation using the existing PPF.

The need to ‘rethink’ the concept of Distribution, both at the planning and operational levels, arises from the emergence of the Distributed Generation paradigm, mostly installed in LV networks. The existing arrangements for the management, protection and control of distribution networks are typically inadequate for this ever-increasing presence of Distributed Generation. Consequently, national and international grid codes have been updated requiring distributed generators to be involved in grid control by supplying ancillary services, such as the voltage and frequency regulation. In this context, the Italian Standards, and in particular the CEI 0–21, require hybrid inverters of residential systems, which are usually only setup to supply active power at unity power factor, to include also the possibility of being able to absorb or supply reactive energy. This allows to limit the over / under voltages problems. To this aim, the inverter manufacturers have introduced the possibility for residential inverters to set the power factor. These new capabilities have been exploited in this paper in order to study the inverter performance with the variation of the power factor, considering both the inductive and the capacitive behaviour. In particular, the presented paper focuses on experimental tests on a hybrid inverter-based system for residential use with the aim of evaluating the dependence of the inverter efficiency on the power factor. Based on measured values, a Matlab/Simulink simulator has been developed for modelling the system, using the found dependence. The main aim is to evaluate the inverter control systems in order to participate in regulation services and to evaluate the inverter efficiency in case of a power factor different from unity.

Recently power systems suffer from harmonic pollution, and the resistances of transmission lines are frequency-dependent due to eddy currents and the skin effect. This frequency dependency should be taken into account, so that apparent power and the power factor accurately reflect transmission loss under non-sinusoidal conditions. A generalised power theory that is applicable to a power system whose transmission/distribution lines have frequency-dependent resistances, and where a unity power factor is given as the minimum loss condition is proposed.

Overcoming the power factor apparent degradation of loads fed by photovoltaic distributed generators