High Efficiency PCS with Scan-Type MPPT Control for a Grid-Connected PV Power Generation System

For a standalone PV （photovoltaic） power generation system, the author previously proposed a new MPPT （maximum power point tracking） control method in which the I-V characteristics are scanned with a detection interval control that operates at specified intervals and monitors the maximum power point. The author has obtained satisfactory results using this new MPPT control method. This paper investigates the application of the new MPPT control method for a PCS （power conditioning system） in a grid-connected type PV power generation system. The experimental results clearly demonstrate that the developed PCS offers outstanding effectiveness in tracking the maximum power point in partially shaded environments.

Testing PV Central Inverters＇ Compliance with International Grid Codes

In many electrical grids worldwide, the rising amount of installed PV （photovoltaic） power entails a considerable influence of PV systems on grid quality and stability. Consequently, in the wake of the revised German medium voltage directives issued in 2009, new requirements for PV inverters have been established internationally. At Fraunhofer ISE＇s Inverter Laboratory, approximately 25 large PV inverters with a nominal power of up to 880 kVA have been characterized in the past three years. In this period, the focus of many inverter manufacturers has begun to shift from traditional European markets towards an international perspective. Therefore, experiences with numerous different grid codes have been gained by our team. This work summarizes the similarities and differences between these grid codes. Additionally, several requirements that have proved to be critical will be examined. Finally, the adequacy of these grid codes to guarantee the safe and reliable operation of electrical grids is discussed.

Impedance Modeling and Stability Analysis of PV Grid-connected Inverter Systems Considering Frequency Coupling

Impedance analysis is an effective method to analyze the oscillation issue associated with grid-connected photovoltaic systems.However,the existing impedance modeling of a gridconnected photovoltaic inverter usually only considers the effect of a single perturbation frequency,ignoring the coupling frequency response between the internal control loops of a grid-connected inverter,which severely affects the accuracy of the stability analysis.Hence,a method of impedance modeling and stability analysis for grid-connected photovoltaic inverters considering cross-coupling frequency is proposed in this paper.First,the generation mechanism of frequency coupling in gridconnected photovoltaic inverters,and the relationship between the coupling frequency and perturbation frequency are analyzed.Secondly,a sequence impedance model of grid-connected photovoltaic systems considering the coupling frequency is established by using the harmonic linearization method.The impact of DC bus voltage control strategy on frequency coupling characteristics of a grid-connected photovoltaic system is evaluated,and the impact of a coupling frequency term on system stability is quantitatively analyzed.Finally,the advantages of the proposed method are verified by several simulations.The results show that the proposed impedance model can accurately predict the potential resonance points of the system,and the coupling frequency characteristics will become much stronger with smaller DC bus capacitance or larger bandwidth of the DC bus controller.

Model predictive control of grid-connected PV power generation system considering optimal MPPT control of PV modules

Because of system constraints caused by the external environment and grid faults,the conventional maximum power point tracking(MPPT)and inverter control methods of a PV power generation system cannot achieve optimal power output.They can also lead to misjudgments and poor dynamic performance.To address these issues,this paper proposes a new MPPT method of PV modules based on model predictive control(MPC)and a finite control set model predictive current control(FCS-MPCC)of an inverter.Using the identification model of PV arrays,the module-based MPC controller is designed,and maximum output power is achieved by coordinating the optimal combination of spectral wavelength and module temperature.An FCS-MPCC algorithm is then designed to predict the inverter current under different voltage vectors,the optimal voltage vector is selected according to the optimal value function,and the corresponding optimal switching state is applied to power semiconductor devices of the inverter.The MPPT performance of the MPC controller and the responses of the inverter under different constraints are verified,and the steady-state and dynamic control effects of the inverter using FCS-MPCC are compared with the traditional feedforward decoupling PI control in Matlab/Simulink.The results show that MPC has better tracking performance under constraints,and the system has faster and more accurate dynamic response and flexibility than conventional PI control.

Single-phase Grid-connected PV System with Golden Section Search-based MPPT Algorithm

Maximum power point tracking(MPPT)is a technique employed for with variable-power sources,such as solar,wind,and ocean,to maximize energy extraction under all conditions.The commonly used perturb and observe(P&O)and incremental conductance(INC)methods have advantages such as ease of implementation,but they also have the challenge of selecting the most optimized perturbation step or increment size while considering the trade-off between convergence time and oscillation.To address these issues,an MPPT solution for grid-connected photovoltaic(PV)systems is proposed that combines the golden section search(GSS),P&O,and INC methods to simultaneously achieve faster convergence and smaller oscillation,converging to the MPP by repeatedly narrowing the width of the interval at the rate of the golden ratio.The proposed MPPT technique was applied to a PV system consisting of a PV array,boost chopper,and inverter.Simulation and experimental results verify the feasibility and effectiveness of the proposed MPPT technique,by which the system is able to locate the MPP in 36 ms and regain a drifting MPP in approximately 30 ms under transient performance.The overall MPPT efficiency is 98.99%.

New inverter topology for ground current suppression in transformerless photovoltaic system application

An interesting inverter topology is proposed in this paper.It is similar to the typical three-phase full bridge inverter from the topology point of view,but smartly designed for the ground current reduction in single-phase photovoltaic(PV)inverter applications.Theoretical analysis is conducted to clarify the operation mechanism of the proposed topology.Performance evaluation is carried out to verify the effectiveness of the proposed topology for the ground current suppression.

基于光伏云平台的智能型光伏并网逆变柜的电气系统设计

介绍了一种基于光伏云平台的智能型光伏并网逆变柜,对其硬件电路的构成、各组成部件的参数设计,以及该逆变柜的工作原理进行了详细介绍。该逆变柜具有低电流畸变率、大容量、高效率、高可靠性的特性,对于基于光伏云平台的光伏并网发电技术领域的工程设计、研究与管理具有参考意义。