Generic Modeling and Control Framework for Power Systems Dominated by Power Converters Connected Through a Passive Transmission and Distribution Grid

In this paper,a compact mathematical model having an elegant structure,together with a generic control framework,are proposed for generic power systems dominated by power converters that are interconnected through a passive transmission and distribution(T&D)grid,by adopting the port-Hamiltonian(pH)systems theory and the fundamental circuit theory.The models of generic T&D lines are developed and then the model of a generic T&D grid is established.With the proposed control framework,the controlled converters are proven to be passive and Input-to-State Stable(ISS).The compact mathematical model is scalable and can be applied to power systems with multiple power electronic converters with generic passive controllers,passive local loads,and different types of passive T&D lines connected in a meshed configuration without self-loops,so it is very generic.Moreover,the resulting power system is proven to be ISS as well.The analysis is carried out without assumptions on constant frequency/voltage,constant loads,and/or lossless networks,except the need of passivity for all parts involved,and without using the Clarke/Park transformations or the graph theory.To simplify the presentation,three-phase balanced systems are adopted but the results can be easily adapted for single-phase or unbalanced three-phase systems.

Comparative Study of Single-phase Phase-locked Loops for Grid-connected Inverters Under Non-ideal Grid Conditions

In renewable power generation systems,ensuring the synchronization of the inverter and the power grid is crucial for the stable operation of grid-connected inverters.Nowadays,the phase-locked loop(PLL)technology has become a widely used grid synchronization method because of its simple implementation and robustness under various grid conditions.Even though a lot of PLLs have been proposed,an overview and comparative analysis of multiple PLLs can be helpful for practical applications.In addition,the weak grid condition is a great challenge for the system.Therefore,this study first presents an overview of the existing PLLs together with their general structures and basic working principles.Depending on the implementation of the phase detector,the PLL can be divided into three categories:power-based PLL(pPLL),orthogonal-signalgenerator-based PLL(OSG-PLL)and adaptive-filter-based PLL(AF-PLL).Then,from the above classification,seven typical single-phase PLLs are selected for further study.Finally,some test results are given,and a comprehensive evaluation of the selected PLLs under different grid conditions is conducted.

Wind energy conversion system using perturb&observe-based maximum power point approach interfaced with T-type three-level inverter connected to grid

In this paper,the performance of a permanent magnet synchronous generator(PMSG)-based wind energy conversion system(WECS)supplied to an uncontrolled rectifier-fed boost converter(BC)interfaced with a three-phase T-type three-level inverter(TLI)has been analysed.The proposed WECS involves three converters,namely an uncontrolled rectifier that is used for conversion from AC to DC;a BC supplied by a PMSG-fed rectifier used to enhance the voltage gain;and a grid-connected three-phase T-type TLI is proposed to eliminate power-quality issues with synchronization of grid voltage and current.The main goal of this research is to model and control the grid-connected T-type TLI using a d-q synchronous frame for wind energy for regulating the DC-link voltage and transferring the generated wind power from the BC to the grid.Furthermore,the perturb&observe(P&O)-based maximum power point(MPP)approach is recommended to keep track of the MPP for a BC that is supplied from a PMSG-based WECS under constant and variable wind speeds.The proposed PMSG-based WECS interfaced with grid-connected T-type TLI using d-q control has been computationally modelled,simulated and validated with constant and variable speeds using MATLAB®and Simulink®.It is confirmed that the P&O-based MPP approach ensures maximum power for varying wind speeds,and the total harmonic distortion of the T-type TLI grid current value is 3.18%,which is within IEEE-519 limits.Furthermore,with grid synchronization,the power factor of the T-type TLI is maintained at unity to avoid power-quality issues.

DC offset rejection in a frequency-fixed second-order generalized integrator-based phase-locked loop for single-phase grid-connected applications

Fast and accurate monitoring of the phase,amplitude,and frequency of the grid voltage is essential for single-phase grid-connected converters.The presence of DC offset in the grid voltage is detrimental to not only grid synchronization but also the closed-loop stability of the grid-connected converters.In this paper,a new synchronization method to mitigate the effect of DC offset is presented using arbitrarily delayed signal cancelation(ADSC)in a second-order generalized integrator(SOGI)phase-locked loop(PLL).A frequency-fixed SOGI-based PLL(FFSOGI-PLL)is adopted to ensure better stability and to reduce the complexity compared with other SOGI-based PLLs.A small-signal model of the proposed PLL is derived for the systematic design of proportional-integral(PI)controller gains.The effects of frequency variation and ADSC on the proposed PLL are considered,and correction methods are adopted to accurately estimate grid information.The simulation results are presented,along with comparisons to other single-phase PLLs in terms of settling time,peak frequency,and phase error to validate the proposed PLL.The dynamic performance of the proposed PLL is also experimentally validated.Overall,the proposed PLL has the fastest transient response and better dynamic performance than the other PLLs for almost all performance indices,offering an improved solution for precise grid synchronization in single-phase applications.