Maximum power point tracking of a small scale compressed air energy storage system

Abstract

This paper is concerned with maximum power tracking of a pneumatically-driven electric generator in a stand-alone small scale compressed air energy storage system (CAES). In this system, an air motor is used to drive a permanent magnet DC generator, whose output is controlled by a buck converter supplying power to a resistive load. The output power of the converter is controlled such that the air motor operates at a speed corresponding to maximum power. The maximum power point tracking (MPPT) controller employs a hybrid perturb and observe method. The rate of change of the converter’s output power with respect to its duty cycle as well as the change of power and duty cycle are used to correct the search direction under transient input power fluctuations. Small speed step changes are used in the vicinity of the maximum power point to improve the accuracy of the search algorithm. However, relatively coarse speed step changes are used when the operating point is far from the MPP to improve the dynamic response of controller and increase its speed of convergence. The analysis and design of the controller is based on a small injected-absorbed current signal-model of the power converter. The controller is implemented experimentally using a real time DSP system. Test results are presented to validate the proposed design and demonstrate its capabilities.

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Identifiers

ORCID for S.M. Sharkh: orcid.org/0000-0001-7335-8503

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