Igor Cvetkovic

Future electronic power distribution systems a contemplative view

Although it has long been argued that electronic power converters can help improve system controllability, reliability, size, and efficiency, their penetration in power systems is still quite low. The often-cited barriers of higher cost and lower reliability of the power converters are quite high if power electronics is used as direct, one-to-one, replacement for the existing electromechanical equipment. However, if the whole power distribution system were designed as a system of controllable converters, the overall system cost and reliability could actually improve, as is currently the case at low power levels within computer and telecom equipment. Starting from the example of a computer power system, the paper contemplates possible future ac and dc electronic power distribution system architectures, especially in the presence of renewable energy sources. The proposed nanogrid-microgrid-…-grid structure achieves hierarchical dynamic decoupling of generation, distribution, and consumption by using bidirectional converters as energy control centers. This is illustrated by the description and simulation of static and dynamic operation of a dc nanogrid in a hypothetical future sustainable home. Several ideas for modeling, analysis, and system-level design of such systems, including power flow control, protection, stability, and subsystem interactions, are presented.

Grid-Interface Bidirectional Converter for Residential DC Distribution Systems—Part One: High-Density Two-Stage Topology

With the emerging installations of multitype renewable energy sources and energy storage elements, the dc electronic distribution systems in residential buildings (dc nanogrid) are becoming an alternative future system solution, achieving a zero net-energy consumption and optimized power management. The concept of the energy control center (ECC), which interconnects the dc system to the traditional ac utility grid, is introduced, and the operation function of ECC converter suitable for dc nanogrid application is defined. This paper investigates a two-stage topology using a full bridge in series with a bidirectional synchronous rectifier dc–dc converter as a single-phase ECC for dc nanogrid, with a significant reduction of the dc-link capacitor value. The operation analysis and the design of passive components are provided. A bidirectional control system and the design process are also presented in terms of the system requirement and the small dc-link capacitor.

Intergrid: A Future Electronic Energy Network?

Anticipated widespread usage of new power electronics technologies in electrical energy generation and consumption is expected to provide major efficiency improvements, while the deployment of smart grid technologies should improve the utilization and availability of electricity. This paper explores possible relationships between these two trends. Starting from an analysis of current and expected trends in the generation, transport, and consumption of electrical energy, this paper contemplates possible future ac and dc electronic power distribution system architectures, especially in the presence of renewable energy sources. The proposed nanogrid-microgrid-Ě-grid structure achieves hierarchical dynamic decoupling of generation, distribution, and consumption by using bidirectional electronic power converters as energy control centers. Several possible directions for modeling, analysis, and system-level design of such systems, including power flow control, protection, stability, and subsystem interactions, are briefly discussed.

Future home uninterruptible renewable energy system with vehicle-to-grid technology

This paper presents the structure and capabilities of a small, grid-interactive distributed energy resource system comprised of a photovoltaic source, plug-in hybrid electric vehicle, and various local loads. Implemented at the residential level, this system, with a plug-in hybrid electrical vehicle, has the ability to isolate a house from the utility grid (intentionally due to a fault or other abnormal grid conditions), work in the standalone mode, synchronize and reconnect to the utility grid, without load power interruptions. Plug-in hybrid electrical vehicles, with a built-in bidirectional power converter, present the opportunity for demand-response operation in the grid connected mode, whereas in the islanded mode, it can perform frequency and voltage regulation of the power bus. In this paper, system structure and modes of operation are described, and measured results are presented for two main modes of operation and mode transitions.

Modes of Operation and System-Level Control of Single-Phase Bidirectional PWM Converter for Microgrid Systems

Robust system control design and seamless transition between various modes of operation are paramount for multifunctional converters in microgrid systems. This paper proposes a control system for single-phase bidirectional PWM converters for residential power level microgrid systems which is robust and can tolerate transitions between the different modes of operation. This is achieved by means of a common inner ac current-loop. Each of the operating modes has an individually designed outer loop performing the corresponding regulation tasks, most commonly including the ac voltage and the dc voltage regulation. A modified , phase-locked loop (PLL) system is used for system-level operation with both small steady-state error and fast response; and a novel islanding detection algorithm based on PLL stability is proposed to facilitate the transition between grid-connected mode and stand-alone mode. Finally, a frequency-response based design procedure for the proposed control system is presented in detail for all operating modes, and its performance is verified experimentally using a DSP-controlled 6 kW 120 V rms (ac)/ 300 V (dc) laboratory converter prototype.

Design of Home Appliances for a DC-Based Nanogrid System: An Induction Range Study Case

Efficiency has become a key design parameter when designing any electrical system. In recent years, significant attention has been paid to the design of optimized micro and nanogrids comprising residential area subsystems. Among the different proposed approaches, one of the most promising consists of a dc-based nanogrid optimized for the interoperation of electric loads, sources, and storage elements. Home appliances are one of the main loads in such dc-based nanogrids. In this paper, the design and implementation of an appliance for operation in a dc-based nanogrid is detailed. An induction heating range is considered as a design example, with some of the design considerations generalizable to any other appliances. The main design aspects, including the inductor system, power converter, and control, are considered. Finally, some simulation and experimental results of the expected converter performance are shown.

Frequency behavior and its stability of grid-interface converter in distributed generation systems

This paper presents a state-feedback model to predict the frequency behavior of the grid-interface converter which uses phase-locked loop (PLL) techniques to synchronize with the grid. The frequency positive-feedback mechanism in the converter system is proposed and quantified in the model. The nonlinear behavior of the PLL under the weak grid condition can be accurately predicted and the large-signal frequency stability region can be also estimated by the proposed model. It shows that large penetration of distributed generation (DG) units, large reactive power variation, and weak grid tends to destabilize the converter frequency operation. The proposed model can help study the electric power system or microgrid operation under a large penetration of renewable energy resources with the power electronic interfaces.

Lithium-based energy storage management for DC distributed renewable energy system

Making electricity grids “smarter” and facilitating them with integration of renewable energy sources (RES) are fairly accepted as the necessary steps to achieve a sustainable power industry. However, serious concerns over reliability and performance require integration of energy storage as a critical part to buffer energy or provide arbitrage. Lithium-based battery offers high specific power/energy density, and gains popularities in many applications, such as (Plug-in) hybrid electric vehicle ((P)HEV) and renewable energy system. This paper discusses two issues: (a) integrating lithium-based battery into a multi-renewable-energy-source-feeding DC-distributed renewable energy system (DRES); (b) floating charge safety for a high voltage series-connected Li-ion battery pack. Based on the analysis of this two issues, this paper then proposes an integration strategy for lithium-based energy storage management, and the maximum cell voltage VCell_max controlled floating charge profile for long string series connected lithium-ion cells pack. An 8.4kW bi-directional multi-phase dc-dc converter is designed to validate above mentioned concepts

A two-stage high power density single-phase ac-dc bi-directional PWM converter for renewable energy systems

It is well-known that single-phase ac-dc conversion requires a bulky dc-link capacitor for filtering the ripple power from the grid. Also, in order to interface a dc renewable energy system to a single-phase utility grid, bi-directional power flow control and dc-bus voltage regulation are major concerns. By using an H-bridge in series with a bi-directional SR dc-dc converter, this paper proposes a two-stage topology as a grid-interfaced single-phase PWM converter which reduces the dc-link capacitor value. A bi-directional control system and a design process are also presented for the dc renewable energy system application. This converter can be easily integrated as a compact power module with intrinsic short-circuit protection ability, small converter volume, and the simplification of the system-level design. A 10 kW prototype and experimental results are presented for the verification purpose.

Unterminated Small-Signal Behavioral Model of DC–DC Converters

The “black-box” modeling of dc–dc converters has always been an attractive topic widely used in engineering practice. However, in order to obtain unterminated model of dc–dc converter, the one had to be removed from the original environment and connected to the high-bandwidth voltage source and current sink for easier decoupling of the source and the load dynamics. This paper addresses an online dc–dc converter characterization procedure where converter under test can remain working in the original environment, at the particular operating point, and be connected to any type of the source and the load while the terminated frequency response characteristics are obtained. The source and the load dynamics can then be decoupled from the measured frequency responses using here proposed linear transformation matrix. The verification and validation of the proposed technique will be both presented in this paper.