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-E-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.

Intergrid: A Future Electronic Energy Network?

This paper introduces a modular multilevel dc/dc converter, termed the DC-MMC, that can be deployed to interconnect HVDC networks of different or similar voltage levels. Its key features include: 1) bidirectional power flow; 2) step-up and step-down operation; and 3) bidirectional fault blocking similar to a dc circuit breaker. The kernel of the DC-MMC is a new class of bidirectional single-stage dc/dc converters utilizing interleaved strings of cascaded submodules. The DC-MMC operation is analyzed and an open loop voltage control strategy that ensures power balance of each submodule capacitor via circulating ac currents is proposed. Simulations performed in PLECS validate the DC-MMC's principle of operation and the proposed control strategy. Experimental results for a 4-kW laboratory prototype illustrate the single-stage dc/dc conversion process for both step-down and step-up operating modes.

A Modular Multilevel DC/DC Converter With Fault Blocking Capability for HVDC Interconnects

Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems. HVDC cables, in particular, play an important role in undersea power transmission and offshore renewable energy integration having lower losses and higher reliability. In this paper, the current commercial feasibility of HVDC cables and the development of different types of HVDC cables and accessories are reviewed. The non-uniform electric field distribution caused by the applied voltage, temperature dependent conductivity, and space charge accumulation is briefly discussed. Current research in HVDC cable for higher operation voltage level and larger power capacity is also reviewed with specific focus on the methodologies of space charge suppression for XLPE extruded cables.

Review of high voltage direct current cables

Conventional dual-active bridge topologies provide galvanic isolation and soft-switching over a reasonable operating range without dedicated resonant circuits. However, scaling the two-level dual-active bridge to higher dc voltage levels is impeded by several challenges among which the high dv/dt stress on the coupling transformer insulation. Gating and thermal characteristics of series switch arrays add to the limitations. To avoid the use of standard bulky modular multilevel bridges, this paper analyzes an alternative modulation technique, where staircase approximated trapezoidal voltage waveforms are produced; thus, alleviating developed dv/dt stresses. Modular design is realized by the utilization of half-bridge chopper cells. This way the analyzed dc-dc transformer employs modular multilevel converters operated in a new mode with minimal common-mode arm currents, as well as reduced capacitor size, hence reduced cell footprint. Suitable switching patterns are developed and various design and operation aspects are studied. Soft-switching characteristics will be shown to be comparable to those of the two-level dual-active bridge. Experimental results from a scaled test rig validate the presented concept.

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Analysis and Design of a Modular Multilevel Converter With Trapezoidal Modulation for Medium and High Voltage DC-DC Transformers

A modular multilevel dc/dc converter, termed the DC-MMC, that can be deployed to interconnect HVDC networks of different or similar voltage levels is introduced in this paper. Its key features include: 1) bidirectional power flow; 2) step-up and step-down operation; and 3) bidirectional fault blocking similar to a dc circuit breaker. The kernel of the DC-MMC is a new class of bidirectional single-stage dc/dc converters utilizing interleaved strings of cascaded sub modules. The DC-MMC operation is analyzed and an open loop voltage control strategy that ensures power balance of each sub module capacitor via circulating ac currents is proposed. Here, we are using the Ann controller. Artificial neuron is supposed to mimic the action of a biological neuron, i.e., to accept many different signals, xi, from many neighboring neurons and to process them in a pre-defined simple way. The goal of the neural network is to solve problems in the same way that the human brain would, although several neural networks are much more abstract.

/pdf/a-modular-multilevel-dc-dc-converter-with-fault-blocking-32bglftsxa.pdf

A Modular Multilevel DC/DC Converter with Fault Blocking Capability for HVDC Interconnects

The interconnected electric power grid is the single largest and most complex machine in the world. Power outages, even for a short interval, have a very low probability but an enormous impact. Transmission systems around the world are facing increasing load demands, and system elements are being pushed toward their thermal limits. Wide-area power trading with varying supply and load patterns is contributing to the ever-increasing congestion. The power grid of the future must be secure, cost effective, and environmental friendly yet reliably integrated and built with intelligent solutions and innovative technologies. High-voltage dc (HVDC) transmission systems are a proven tool in tackling these challenges.

E. Fullerton

Papers

Magic Bus: High-Voltage DC on the New Power Transmission Highway