Abstract: An error-compensating inertial measurement unit includes a high dynamic range six degree of freedom inertial measurement unit and a nine degree of freedom inertial measurement unit, both strongly attached to a rigid substrate. A sensor processor determines a magnitude of mathematical difference between an orientation determined from the six degree of freedom inertial measurement unit and an orientation determined by a fusion processor in the nine degree of freedom measurement unit. When the magnitude of difference is greater than a sensor drift threshold, the absolute orientation of the six degree of freedom inertial measurement unit is modified to the orientation determined from the nine degree of freedom inertial measurement unit. When the nine degree of freedom inertial measurement unit estimates that its measurement accuracy is reduced by sensor saturation, modifying the absolute orientation of the six degree of freedom inertial measurement unit is delayed.

Abstract: A compressed-air energy storage system according to embodiments of the present invention comprises a reversible mechanism to compress and expand air, one or more compressed air storage tanks, a control system, one or more heat exchangers, and, in certain embodiments of the invention, a motor-generator. The reversible air compressor-expander uses mechanical power to compress air (when it is acting as a compressor) and converts the energy stored in compressed air to mechanical power (when it is acting as an expander). In certain embodiments, the compressor-expander comprises one or more stages, each stage consisting of pressure vessel (the “pressure cell”) partially filled with water or other liquid. In some embodiments, the pressure vessel communicates with one or more cylinder devices to exchange air and liquid with the cylinder chamber(s) thereof. Suitable valving allows air to enter and leave the pressure cell and cylinder device, if present, under electronic control.