Roghayeh Gavagsaz-Ghoachani

Control of a Hybrid Energy Source Comprising a Fuel Cell and Two Storage Devices Using Isolated Three-Port Bidirectional DC–DC Converters

This paper deals with a hybrid energy source consisting of a proton exchange membrane fuel cell, two storage devices, and a load. Generally, this type of source constitutes of nonisolated dc–dc converters. In order to have galvanic isolation for safety reasons and a high voltage ratio, we introduce another system based on the use of three-port isolated dc–dc converters. The storage device can be either a battery or a supercapacitor. This paper presents a control strategy for the hybrid source and includes a global efficiency analysis of power sharing between modules. The proposed system is validated through different simulation results. Additionally, some experimental results are given for the single module operation.

Stability Analysis and Dynamic Performance Evaluation of a Power Electronics-Based DC Distribution System With Active Stabilizer

The stability of dc microgrids is influenced by the nonlinear behavior of the converter-controlled loads with constant power characteristics. This nonlinear dynamic, in line with reduced size input filters used in the embedded power distribution of transportation systems, has a degrading effect on the dynamic performance and stability of the system. This paper presents the complete stability analysis of a dc distribution system composed of power electronics-based source and load. For this objective, a discrete-time dynamic model is developed and is applied to the studied system. Here, for the first time, the dynamic effect of the load controller is taken into the system model. In the studied system, the load converter is connected in cascade with the rest of the system, and is equipped with an input LC filter, representing a common distributed architecture for the transportation applications. The controller of the source converter employs an active stabilizer to extend the stability margin of the system. This stabilizer uses high-pass-filtered voltage of the dc bus following with a proportional compensator. The dynamic behavior of the controller and the stabilizer is experimented through a series of laboratory tests. Different load dynamics are implemented to demonstrate the impact of slow and fast load dynamics on the stability of the system.

Original article: Predicting the onset of bifurcation and stability study of a hybrid current controller for a boost converter

The proposed method develops a continuous-time averaging model of a nonlinear current controller for a continuous conduction mode (CCM) boost converter in the lack of a closed outer voltage loop. The controller associates peak-current and sliding mode controls. The advantages of the proposed approach are the capability to show the onset of fast-scale bifurcation, and the reduction of numerical calculation effort. To confirm the validity of the proposed method, simulation and experimental results are detailed.

Discrete-time modelling, stability analysis, and active stabilization of dc distribution systems with constant power loads

This paper presents the stability analysis of a dc distribution system supplying multi-converter loads. The load converters are tightly controlled, behaving as constant power load with low damped LC input filters. The dynamic behavior of the system in high frequency range is often not studied with the classical tools based on average linearization. Whereas, small LC filters with high cutoff frequency are common in transportation systems. Therefore, in this paper, the stability analysis of the system is established based on a discrete-time model of pulse width modulated converters considering the switching effect and intrinsic nonlinearities of the system. The impacts of the filter parameters and interactions among the loads are investigated with the discrete-time method. Moreover, an active stabilizer is included in the system model in order to extend the stability domain. Experimental results, conducted on a dc distribution system, are given in order to validate the analytical stability analysis and stabilizer.

New Method to Filter HF Current Ripples Generated by Current-Fed DC/DC Converters

This paper presents a new method for filtering the HF current ripple generated by current-fed dc/dc converters. This method is based on the use of an active filter connected in parallel with the source, without any passive filter between the source and the power converter. The design of this new active filter and its associated controllers are fully explained in the paper. Experimental results validate the proposed filtering method. The structure of the proposed active filter is patented at the World Intellectual Property Organization under the number WO/2008/132318.

Stability analysis of a tightly controlled load supplied by a DC-DC boost converter with a modified sliding mode controller

It is common in transportation systems to have small LC filters connected to constant power loads. That may lead to instabilities. To stabilize the system without increasing its weight and volume, a new control scheme is studied, based on a sliding mode controller. It is applied to a DC-DC boost converter that supplies a constant power load. The stability analysis is done using discrete-time model to obtain a Jacobian matrix. Eigenvalues of the Jacobian matrix are calculated to conclude about the stability. Simulations and experimental results are given to validate the modified control.

Asymptotic Stability Analysis of the Limit Cycle of a Cascaded DC–DC Converter Using Sampled Discrete-Time Modeling

Small LC filters connected to tightly controlled power loads may lead to instabilities. With small LC filters comes a high cutoff frequency, and the conventional stability analysis based on an average model may not be precise enough. Other tools based on another model are required to study this type of system. In this paper, a new discrete-time model is proposed to investigate the behavior of the studied system and to take into account the switching effect. Then, the stability analysis of the limit cycle is done using Floquet multipliers. This system is composed of a dc-dc boost converter, an LC filter, and a controlled power load. Simulation and experimental results are given to validate the proposed model and analysis.

DC power networks with very low capacitances for transportation systems: Dynamic behavior analysis

It is known that conventional analysis based on average models can be used only if the cutoff frequency of the filter is much lower than the switching frequency. For networks with very low capacitances, the cutoff frequency is close to the switching frequency so other tools are required for analyzing the behavior of the system. Such a tool is proposed in this paper and is applied to predict chaotic, multiperiodic or stable behavior of cycles defined by state variables of the system. A permanent magnet synchronous motor-drive system constituted by a dc power source supplying an LC filter connected to a tightly controlled motor is studied. A very low capacitance is provided such that the switching effects due to power electronics device can no more be neglected. Experimental results confirm the validity of the proposed tool.

Dynamic analysis of an on-board DC distribution system with active stabilizer

Stability of onboard dc power systems is influenced by nonlinear behavior of converter-controlled loads with constant power characteristics. This nonlinear dynamics, in line with reduced size input filters used in transportation systems, has a degradation effect on the dynamic performance and stability of the system. This paper addresses stability study of a dc power system with an active stabilization system. Different load power dynamics are implemented to demonstrate the impacts of slow and fast load dynamics on the stability of the system. Performance of the stabilizer, in steady state and transient, is also investigated through a series of experimental tests.

Stability analysis, discrete time modeling and active stabilization of DC-DC converter, taking into account the load dynamics

For stability analysis, it is often chosen to model power loads by constant power loads (CPL). However, this model may be too strict, as it is the worst case scenario. In this paper, it is intended to change the model of a power load to increase the calculated stability zone of a DC system composed of a source converter, an LC filter and the power load. A stabilization term is included in the command of the source in order to increase the power range. The simulation and experimental results that are given to validate the proposed model and to demonstrate the effectiveness of the proposed stabilizer and its tuning.