Analysis and Performance Evaluation of a Two-Stage Resonant Converter for Wide Voltage Range Operation

This paper proposes a two-stage isolated dc-dc converter for electric vehicle charging applications, where high efficiency over a wide range of battery voltages is required. It employs a first pre-regulation stage and a second half-bridge LLC stage, integrated with the first. The second stage is always operated at resonance, ensuring very high efficiency. The first pre-regulation stage is responsible for the desired input-to-output voltage conversion ratio and the zero-voltage switching operation of all the switches. This allows low conversion losses even with voltages that may vary over a wide range. The conversion structure is shown considering a first experimental prototype that interfaces a 750-V dc-link with an output bus with nominal voltage range 250V-500V. The implemented module is rated 5 kW and achieves a peak efficiency of 98.0% at 3 kW output power

Generalized Control of the Power Flow in Local Area Energy Networks

Local area energy networks (E-LANs) are cyber-physical systems whose physical layer is a meshed low-voltage microgrid fed by a multiplicity of sources, i.e., utilities, energy storage systems, and distributed power sources. The cyber layer includes distributed measurement, control, and communication units, located at end-user premises, as well as centralized supervision and dispatchment control. As compared with standard microgrid, the E-LAN encompasses the ability for end-users to actively contribute to the operation of the microgrid while acting as independent energy traders in the electrical market. Operational goals include active contribution of end-users to power sharing, loss reduction, voltage stability, demand response, fault identification and clearing, isolation of sub-grids for maintenance, islanding, and black start. Economic goals include the possibility, for each end-user, to decide in every moment, based on convenience, how his energy and power capacity is shared with other users, e.g., for demand response or to trade energy in the electric market. This paper introduces a comprehensive theoretical approach of E-LAN control to achieve all the above operational goals while providing a high level of dynamic protection against faults or other events affecting the system functionality, e.g., overloads or fast transients. It shows that meshed microgrids are the necessary infrastructure to implement the desired functionalities

Rapid prototyping of digital controllers for microgrid inverters

A rapid prototyping methodology for digital controllers is presented in this paper. Its main application is in the development, debugging, and test of microgrid inverter controllers. To fulfill the application requirements, these systems are characterized by complex multilayer architectures, extending from PWM and current control loops up to global optimization and high level communication functions. The complexity and the wide variability of the different layer implementations make digital control mandatory. However, developing so complex digital controllers on conventional hardware platforms, like DSPs or even FPGAs, is not the most practical choice. The paper shows how multi-platform control devices, where software configurable DSP functions and programmable logic circuits are efficiently combined, represent the optimal solution for this field of application. Furthermore, the paper proposes hardware-in-theloop real-time simulation as an effective means of developing and debugging complex hardware and software co-designed controllers. A case study is presented and used to illustrate the different design and test phases, from initial concept and numerical simulation to final experimental verification

A Flexible Energy Gateway for Hybrid Nanogrids

This paper presents the topology and control of a three-port energy gateway for hybrid ac/dc nanogrids. The simple hardware architecture allows to connect renewable energy generators, energy storage devices, like ultra-capacitors, and the utility grid through three different interface converters, which, altogether, define the three-port energy gateway of the nanogrid. The proposed energy gateway represents a trade-off between circuit complexity and control flexibility, allowing i) operation of the energy storage port over a wide voltage-range, ii) control of the local dc-bus voltage at a predefined set-point, iii) multi-directional power flow, iv) support of the local ac-bus voltage with possibility to transition into islanded operation. A hierarchical control strategy is presented that enables flexible power exchange between the ac and dc buses. At the top of the control hierarchy, a human-machine interface is dedicated to operation mode selection and parameter preset; then, a supervisory control layer is present for system-level monitoring and control functions; the lower layer of the hierarchy is constituted by converter control functions for power flow regulation, achieved leveraging on voltage and current controllers. The flexibility and effectiveness of the proposed energy gateway architecture, control, and implementation are demonstrated in the paper in a variety of operation modes by means of experimental results

A Per-Phase Power Controller allowing Smooth Transitions to Islanded Operation

This paper presents a droop-based controller for grid-tied three-phase inverters. The controller allows to regulate the inverter output power while operating grid-tied, to support the local grid voltage while operating islanded, and to seamlessly transition into this latter mode of operation. The use of the traditional droop control scheme for per-phase power control would lead to unequal frequencies among the phase voltages, which is not acceptable. Instead, the proposed controller allows independent power references tracking at each of the phases of a three-phase inverter while grid-tied and a proper transition into the islanded operation. Per-phase power control is crucial for several important services in modern smart power networks, like demand-response and distributed unbalance compensation. Simulation and experimental results considering a laboratory-scale prototype are reported and discussed to validate the proposed controller

Black-Box Large-Signal Average Modeling of DC-DC Converters Using NARX-ANNs

This paper investigates the use of non-linear autoregressive exogenous (NARX) artificial neural networks (ANNs) to achieve black-box average dynamic models of dc-dc converters capable of capturing the main converter non-linearities. Non-linearities may include, for example, dynamic behavior variations due to changes of operating point or operating mode (e.g., discontinuous conduction mode, continuous conduction mode). This paper presents design guidelines for determining the NARX-ANN architecture and the dataset to be used in the training process. Dataset definition includes the choice of the perturbations for stimulating the aimed system behaviors and optimizations for dataset size reduction. The proposed approach is first derived for a dc-dc boost converter. To verify the generality of the proposed method, the same methodology is also applied to a Ćuk converter. In both cases, the proposed NARX-ANN modeling provided accurate results, with only limited deviations observed in the time-domain responses to step variations of duty-cycle and output current. The proposed model provided accurate small-signal behavior under different operating conditions. The validity of the approach is evaluated experimentally by considering a boost converter prototype