Hugues Renaudineau

Flatness-Based Control of Three-Phase Inverter With Output

Recently, hybrid electrical power sources composed of storage elements and renewable energy sources are known to have made great development. These energy sources are connected to a dc bus and need a dc-to-ac converter to transfer the produced energy to the grid. Three-leg voltage source inverters equipped with an output LC filter are often used. The main objective of this stage is to generate a three-phase sinusoidal voltage with defined amplitude and to ensure the smallest harmonic distortion rate of the output voltage for any load conditions. To satisfy the defined objectives, we present in this paper a new control method based on differential flatness control technique. The main interest of this control method is the possibility to define the behavior of the state variable system in the steady state as well as in transients. The use of only one control loop allows obtaining high dynamic properties of the system which ensure small harmonic distortion rate of the output voltage. Experimental results under balanced, unbalanced, and nonlinear load conditions are presented and validate the effectiveness of the proposed control methods.

LC

In this paper, a new current sharing technique on a general case of N paralleled DC-DC boost converters is presented. The proposed optimization is based on the knowledge of individual boost parameters. Every loss through the structure are modeled by equivalent resistors. Using an accurate online estimation of those resistors, the losses through each individual converter can be determined. Then, a new current sharing scheme is defined aiming to maximize the global efficiency of the overall structure. To verify the proposed method, simulations and experiments have been realized on a three-parallel boost converters structure.

Filter

For large-scale photovoltaic (PV) systems, the multistring configuration is becoming more and more attractive compared with the classical central inverter, since it results in better energy yield by realizing distributed maximum power point tracking. Among the existing solutions, an attractive topology consists in a single dc bus bar collector cascaded H-bridge (CHB) inverter. Through the use of a single dc bus bar collector, the CHB inverter presents inherent balanced operation while the multistring PV-system is fully decoupled from the grid-tie inverter. This paper proposes the experimental validation of this structure on a reduced-size single-phase laboratory prototype. Results confirm the interest of the proposed PV multistring architecture.

Efficiency Optimization Through Current-Sharing for Paralleled DC–DC Boost Converters With Parameter Estimation

This paper develops a robust tool for handling ac side stability issues occurring in LCL-filter-based grid-connected converters.LCL filters give advantages in cost and dynamic as smaller inductors employed compared with L filters for the same required damping of the switching harmonics. Nevertheless, the additional poles introduced by the LC part induce resonance in the system leading to stability problems. To deal with this stability issue, a new damping method based on the generalized circle criterion is proposed in this paper. The large signal nature of the applied theory allows obtaining high damping efficiency and robustness under large variations of the grid impedance. A theoretical analysis and the experimental results are presented to show the effectiveness of the proposed compensating method.

Experimental Validation of a Single DC Bus Cascaded H-Bridge Multilevel Inverter for Multistring Photovoltaic Systems

In order to increase the conversion efficiency in photovoltaic (PV) systems, different configurations and topologies were developed. Depending on the application, the converters used for grid connection are built using one or two conversion stages. The advantages of the converters with a DC-stage are mainly the distributed maximum power point tracking algorithm per PV string, a wider range of operation, higher energy yield and, when required for grid connection, the possibility of voltage regulation. However, the conversion efficiency is lower than configurations with a single stage as the central inverter. Therefore, the proposed work presents a Partial Power DC-DC converter (PPC) which process part of the entire system power, and the surplus power is directly supplied to the output side. A topology is proposed and the details of its operation are explained based on the operating principle. Simulations are performed in order to evaluate the converter performance.

Large signal stability analysis and stabilization of converters connected to grid through LCL filters

In order to increase the conversion efficiency in photovoltaic (PV) systems, different configurations and topologies were developed. Depending on the application, the converters used for grid connection are built using one or two conversion stages. The advantages of the converters with a DC-stage are mainly the distributed maximum power point tracking algorithm per PV string or PV module and, when required for grid connection, the possibility of voltage elevation. However, the conversion efficiency is lower than configurations with a single-stage as the central inverter. Therefore, the proposed work presents a Partial Power DC-DC converter (PPC) which process part of the entire system power, and the remaining power is directly supplied to the output side. A topology is proposed and the details of its operation are explained based on the operating principle. Simulations are performed in order to evaluate the converter performance.

Partial power DC-DC converter for photovoltaic two-stage string inverters

Central inverters are the most common configuration for large-scale photovoltaic systems. Under partial shading or any non-uniform conditions on the photovoltaic plant, several power maxima may arise. Conventional perturb and observe and other classical maximum power point tracking algorithms are capable of tracking a local maximum, but can not guarantee to operate at the global maximum. A solution to such limitation is to perform a scan of the photovoltaic characteristic periodically in order to ensure operation at the global maximum. However, such a scan generates high output power variations that may not comply with grid codes. In order to overcome this drawback and allow a global scan for maximum power point tracking purposes, this paper proposes a hybrid photovoltaic system with an ultra-capacitor-based energy storage system. Simulations are provided to validate the proposed configuration. Results show that the photovoltaic scan allows operation at the global maximum power point, while the ultra-capacitor bank manages the power transient so that the power output fluctuation is kept within grid-code limits.

Partial power DC-DC converter for photovoltaic microinverters

This article presents some applications for our mathematical model of lithium-ion battery. This model is based on Newmans works, and includes migration and diffusion of species and charges in electrodes and electrolyte, electric double layer capacitance, and solid-electrolyte interface layer. Using electrical analogies of transport phenomena, it is directly implemented in standard simulation software used in electrical engineering. The paper recalls the fundamental model of lithium-ion battery. Then, it briefly explains how the analog model is obtained from mass and charge transport equations. At last, some examples of simulation are shown (lithium plating abacus, electrochemical impedance spectroscopy, including SEI) to demonstrate the advantages of our modeling method.

Energy storage system for global maximum power point tracking on central inverter PV plants

In conventional photovoltaic microinverters configuration, a single PV module is connected to the grid through two converter stages: a step-up dc-dc stage and a step-down dc-ac stage. In the first stage, a high frequency transformer is generally used to achieve the high step-up voltage ratio conversion to a voltage above the grid peak value, reducing the converter efficiency while increasing its size. More recently single-stage step-up dc-ac configurations have been proposed to overcome these problems. However, they increase control complexity, and efficiency remains an issue due to the high step-up ratio required and being a single stage. Therefore, a two-stage configuration consisting of two consecutive step-up converters is proposed in this paper. With this scheme, it is possible to distribute the elevation effort to improve the global efficiency of the PV microinverter. The proposed topology merges a traditional boost dc-dc converter for the first stage, like in the conventional configuration, but operating with a below-grid-peak-voltage dc-link voltage. A step-up inverter is used for the second stage; it is composed of two boost converters connected in differential mode (dual boost inverter). Simulation results are provided to validate the proposed configuration.

A mathematical lithium-ion battery model implemented in an electrical engineering simulation software

In the recent years growing interest has been given to photovoltaic (PV) microinverters. Sub-modular optimization of PV panels where the junction-box of the panel is removed and each sub-modules is connected to an individual DC-DC converter realizing independent MPPT is one promising solution especially for systems subject to partial shading. In this paper, individual flyback DC-DC converters are considered to realize the MPPT as well as the voltage elevation required for grid connection of a microinverter. This paper aims to show the interest of using cascaded H-bridges for realizing the DC-AC conversion, compared with a single H-bridge inverter. Simulation results are provide to show the improvement realized by using cascaded H-bridge inverters in a sub-module microinverter architecture, both in term of efficiency and power quality.