This paper surveys the control theoretic literature on decentralized and hierarchical control, and methods of analysis of large scale systems.

Survey of decentralized control methods for large scale systems

Overall structure of electrical power system is in the process of changing. For incremental growth, it is moving away from fossil fuel based operations to renewable energy resources that are more environmentally friendly and sustainable. At the same time it has to grow to meet the ever increasing need for more energy. These changes bring very unique opportunities and obstacles. Over the past few decades many new and innovative ideas have been explored in the broad area of energy storage. They range in size, capacity and complexity in design. Some of the systems are designed for applications in large scale power and others are performing short term energy storage ride through capabilities for critical manufacturing and technology systems. Energy storage technology has become an enabling technology for renewable energy applications and enhancing power quality in the transmission and distribution power systems. This paper summarizes all the advancements made and provide a composite picture of costs and trends in storage technologies.

Advancement of energy storage devices and applications in electrical power system

During periods of vehicle inactivity, a vehicle-based APU electric generating system may be coupled into a regional electric grid to send electricity into the grid. A currently-preferred APU is a solid oxide fuel cell system. When a large number of vehicles are thus equipped and connected, substantial electric buffering can be effected to the grid load. A vehicle-based APU can also function as a back-up generator to a docking facility in the event of power failure of the grid. Gaseous hydrocarbon is readily supplied by pipe in many locations as a commercial and residential heating fuel source, and a hydrocarbon reformer on the vehicle can be attached to the fuel source, enabling an APU to operate as a stationary power source indefinitely. An optional storage tank on the vehicle may be refueled with gaseous fuel, for example, while the battery is being electrically recharged by the grid.

Electric vehicle having multiple-use apu system

An exemplary power system may include an electric machine with multiple sets of stator windings, each set of windings being coupled through a separate switch matrix to a common voltage bus, and each of which may be spatially arranged in full pitch around the stator such that stator flux harmonics are substantially reduced. The reduced stator flux harmonics may be associated with phase current harmonic content. In an example application, such power systems may operate in a generating mode to transfer mechanical energy to electrical energy on a DC voltage bus. In some illustrative embodiments, the power system may provide both high-power and high-speed (e.g., 1MW at 8000 rpm or above) motoring and/or generating capability suitable, for example, for on-board (e.g., marine, aviation, traction) power systems.

Electromechanical energy conversion systems

A review of thermal energy storage in compressed air energy storage system

A combustion turbine power generation system includes a modified simple cycle combustion turbine power generation system optimized for a "hot" stand-by reserve mode of operation and having a power shaft assembly including a compressor, an expansion turbine, and a double-ended motor/generator between the compressor and the turbine. The motor/generator has a turbine driving clutch structure on one end thereof and a compressor driving clutch structure on the other end thereof. A combustor feeds the expansion turbine. The power generation system includes an additional system having a boost compressor, an intercooler feeding cooled air to the boost compressor an electric motor for driving the boost compressor, and aftercooler downstream of the boost compressor. A compressed air energy storage is downstream of the aftercooler. The additional system is integrated with the modified simple cycle combustion turbine power generation system to provide (i) a primary mode of operation--a hot stand-by mode, when the plant is ready to deliver an emergency power at full turbine power of specified duration within a few seconds; (ii) a cold start-up mode of operation, when the plant is ready to deliver an emergency power at full turbine power of specified duration within a few minutes, depending on the specifics of the turbine design, (iii) an emergency power supply mode, when the plant provides emergency power at full turbine power of specified duration; (iv) a combustion turbine emergency power supply mode, when the plant provides approximately 50% of full turbine power of unlimited duration during long term interruptions of the power supply; and (v) a storage charging mode of operation to charge the air storage.

Method for providing emergency reserve power using storage techniques for electrical systems applications

Comparative results are presented for the performance and cost data of 25MW-220MW compressed-air energy storage (CAES) power plants. The data include steady-state and dynamic load following characteristics, turbomachinery versus storage costs and siting flexibility for this type of energy storage power plant. Also presented is a description of the various types of air storage geologic formations available in about 3/4 of the United States.

Compressed -Air Energy Storage (CAES): Overview, Performance and Cost Data for 25MW to 220MW Plants

This paper discusses the different initiatives that utility decision makers have set in place to address the vulnerability of the US power grid to physical and cyber attacks. One of the efforts to enhance grid security is EPRI's Infrastructure Security Initiative (ISI), which was designed to develop both prevention countermeasures and enhanced recovery capabilities. To protect against cyber attacks, several organizations were also established including the Computer Emergency Response Team (CERT) and the Process Control Systems Forum (PCSF). In addition, EPRI also launched the Energy Information Security (EIS) program to focus on computer-based security breaches. An industry-wide cybersecurity program alliance, called the PowerSec Initiative, was also formed to address the cyberthreat issue as it could impact electric utility operational and control equipment.

Electric utility responses to grid security issues

A compressed air energy storage (CAES) system encompassing direct heating. The compressed air energy storage system includes a compressor for compressing ambient air, an air storage reservoir, and a thermal energy storage system. The air storage reservoir is adapted to store compressed air from the compressor. The thermal energy storage system is adapted to supply heat to the compressed air energy storage system such that the compressed air is heated to increase work production of the compressed air. The thermal energy storage system is heated using off-peak electricity.

Energy storage system

An open circuit liquid cooled gas turbine in which a coolant passes through the turbine blades and is expelled at the tips thereof The coolant is recaptured by providing ports in the turbine casing in radial alignment with the turbine blades whereby fluid expelled radially is received by the ports A trough is provided in the turbine casing axially displaced downstream from the turbine blades to recapture coolant that is blown by the ports due to the differential pressure in the turbine

Robert B. Schainker

Papers

Method for providing emergency reserve power using storage techniques for electrical systems applications

Compressed -Air Energy Storage (CAES): Overview, Performance and Cost Data for 25MW to 220MW Plants

Electric utility responses to grid security issues

Energy storage system

Method and means for recapturing coolant in a gas turbine