A hybrid method for maximum power tracking of a small scale CAES system

This paper is concerned with maximum power tracking of a pneumatically-driven electric generator in a standalone 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 uses a hybrid perturb and observe search algorithm. It utilizes the power-speed curve when it is near the maximum power point (fine tuning). When it is far from the maximum power point, it uses the more sensitive power-duty cycle characteristic of the buck converter generator system (coarse tuning). 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 dSPACE system. Test results are presented to validate the proposed design and demonstrate its capabilities.