Single-phase Synchronous Reference Frame Research Articles

Reactive Power Management in Solar PV System using Matlab

Photovoltaic (PV) systems propose attractive alternative source of generation because these can be placed near to the load centers when compared with other renewable source of generation. It is therefore rooftop PV is the center of attraction for majority PV systems. The rooftop PV system in general is grid connected and supports the off-grid load with battery backup. The designed system must ensure total evacuation of generated power and with high efficiency of conversion, and utilizes the resource adequately to maximize the utilization of energy. This paper proposes single phase synchronous reference frame (SRF) theory based current controlled PWM controller for the voltage source converter (VSC) to realize maximum generated power evacuation by maintaining the DC link voltage constant without battery support, low THD sinusoidal line synchronized current output, and limited reactive power compensation based on the unutilized capacity of the inverter. PV power is being tracked always at MPP through incremental conductance (IC) method. MATLAB based simulation results shows the efficient working of rooftop PV with proposed control algorithms in grid connected mode with limited reactive power conditioning.

A Single-Phase Globally Stable Frequency-Locked Loop Based on the Second-Order Harmonic Oscillator Model

This paper presents a novel frequency-locked-loop (FLL) scheme that provides estimates of the in-phase and square-phase fundamental components of a distorted single-phase reference signal and an estimate of its fundamental angular frequency. The main feature of the proposed scheme is that its design is fully based on the dynamical model of a single-phase signal generator, namely, the second-order harmonic oscillator (SOHO), which adds originality to the scheme. In fact, the proposed scheme owns a particular structure involving a set of orthogonal signals, which can be seen as the fixed-frame representation of three-phase balanced signals. Additionally, a plug-in block is included as a mechanism to mitigate the effect of the harmonic distortion. A proof of global stability for the proposed scheme based on nonlinear argumentation is also included, which contributes to the novelty of the work and ensures convergence disregarding the initial conditions of the to-be-estimated signal components. In addition, explicit conditions are presented for the tuning of control parameters. Experimental results corroborate the performance of the proposed scheme under angular frequency variations, phase jumps, voltage sags and harmonic distortion on the reference signal. For comparison purposes, also the state-of-the-art second-order-generalized-integrator-based FLL and the single-phase synchronous-reference frame phase-locked loop are tested.

Development of Frequency Fixed Sliding Discrete Fourier Transform Filter Based Single-Phase Phase-Locked Loop

The single-phase phase-locked loop (PLL) is essential for the stable operation and control of single-phase grid-connected converters. However, in practical applications, the grid voltage is usually affected by harmonics and dc offset, which will cause errors in the output of the PLL. Therefore, using sliding discrete Fourier transform filter (SDFT) as a prefilter, this paper proposes an improved single-phase synchronous reference frame PLL with a fixed sampling frequency, which can accurately and quickly obtain the grid parameters under distorted grid conditions. Most importantly, the paper theoretically analyzes phase and amplitude errors generated by SDFT for the first time and a quantitative compensation method is proposed, which is straightforward to be used by a reader. Finally, the proposed PLL is compared with other PLLs through simulation and experiments. The experimental results show the effectiveness and practicability of the proposed method.

A Simple Approach to Reject DC Offset for Single-Phase Synchronous Reference Frame PLL in Grid-Tied Converters

Synchronous reference frame phase-locked loop (SRF-PLL) is widely used for grid voltage synchronization in single-phase grid-connected power converters. However, in the actual situation, dc offset component may be introduced in the input of the PLL, due to the transient fault of the power grid, sampling and measurement error, or A/D signal processing. A simple yet effective approach with additional all-pass filter based dc rejecter is presented for SRF-PLL, in this paper. Thereby, correct estimation and undesirable periodic ripple free can be achieved in SRF-PLL, when the input signal contains dc offset. The second order generalized integrator based PLL (SOGI-PLL) is first introduced, followed by the analysis on influence of the input dc offsets in SRF-PLL. The structure of enhanced-SOGI (ESOGI) with its analysis of dc offset rejection effects and performance have been then formulated in detail. Finally, experimental results are presented to demonstrate the effectiveness of the proposed ESOGI based PLL.

Mathematical and Experimental Investigation on Advanced PLL for Cascaded H-Bridge Multilevel Inverter in Active Filtering Application

Cascaded H-bridge multilevel inverter (CHB-MLI)-based shunt active power filter (SAPF) is one of the finest solutions for power quality improvement in case of medium-voltage distribution sector. Performance of SAPF degrades due to the presence of DC offset and harmonics in the grid voltage since this will result phase angle and frequency error. Therefore, modified single-phase synchronous reference frame theory comprising of advanced PLL is presented in this article. The advanced PLL can track frequency and phase angle accurately even though source voltage is having DCor harmonic content. A detailed mathematical modeling and stability analysis of this PLL is presented using Routh-Hurwitz criteria. A novel systematic design procedure using gravitational search algorithm (GSA) and an Eigen value analysis is proposed for calculating optimal PLL parameters. Closed-loop SAPF control stability is tested using root-locus analysis. An extensive experimental analysis of the proposed control applied to CHB-MLI-based SAPF has been performed under distorted source voltage and non-linear loading conditions to show the effectiveness of the proposed control over recently published work. Source current maintains its sinusoidal shape, properly synchronized with grid voltage and having distortion limit in compliance with IEEE-519 standard irrespective of source voltage conditions during the operation of SAPF.

Modified Single Phase SRF d-q Theory Based Controller for DVR Mitigating Voltage Sag in Case of Nonlinear Load

This paper mainly concentrates on design of improved controller and its implementation based on single phase synchronous reference frame theory (SRFT) for Dynamic Voltage Restorer (DVR) compensating voltage sag particularly for nonlinear load. In case of single phase distribution line with nonlinear load, the complexity of controller’s design becomes more serious issue. The present single phase and/or three phase theories applicable to DVR shows poor response to restore voltage sag in case of nonlinear load due to presence of harmonics. Hence restoration of voltage sag in single phase nonlinear load connected system has been a serious concern. Therefore, new controller for DVR has been proposed incorporating effective design concept for fundamental component extraction in case of nonlinear load. The single phase SRFT based main controller for DVR works on two separate closed path viz. feed forward path for quick transient response and feedback path for reducing the steady state error. Moreover, pre-sag mitigation strategy of DVR has been adapted through these two aforementioned paths. Complete design of proposed controller is based on phasor analysis. It also consist of proportional integral (PI) controller to reduce the error in the DC-link voltage during compensation time. The controller performance has been verified in MATLAB Simulink for both types (linear and nonlinear) of load. The results obtained indicates that the proposed controller is effective in its performance.