Maximum Power Point Tracking of a Small-Scale Compressed Air Energy Storage System

Abstract

The thesis is concerned with a small-scale compressed air energy storage (SS-CAES) system. Although these systems have relatively low energy density, they offer advantages of low environmental impact and ease of maintenance.The thesis focuses on solving a number of commonly known problems related to the perturb and observe (P&O) maximum power point tracking (MPPT) system for SS-CAES, including confusion under input power fluctuation conditions and operating point dither.A test rig was designed and built to be used for validation of the theoretical work. The rig comprised an air motor driving a permanent magnet DC generator whose power output is controlled by a buck converter. A speed control system was designed and implemented using a dSPACE controller. This enabled fast convergence of MPPT.Four MPPT systems were investigated. In the first system, the air motor characteristics were used to determine the operating speed corresponding to MPP for a given pressure. This was compared to a maximum efficiency point tracking (MEPT) system. Operating at the maximum power point resulted in 1% loss of efficiency compared to operating at the maximum efficiency point. But MPPT does not require an accurate model of the system that is needed for MEPT, which also requires more sensors.The second system that was investigated uses a hybrid MPPT approach that did not require a prior knowledge system model. It used the rate of change of power output with respect to the duty cycle of the buck converter as well as the change in duty cycle to avoid confusion under input power fluctuations. It also used a fine speed step in the vicinity of the MPP and a coarse speed step when the operating point was far from the MPP. Both simulation and experimental results demonstrate the efficiency of this proposed system. The third P&O MPPT system used a fuzzy logic approach which avoided confusion and eliminated operating point dither. This system was also implemented experimentally.A speed control system improved the controllable speed-range by using a buck-boost converter instead. The last MPPT system employed a hybrid P&O and incremental inductance (INC) approach to avoid confusion and eliminate operating point dither. The simulation results validate the design.Although the focus of the work is on SS-CAES, the results are generic in nature and could be applied to MPPT of other systems such as PV and wind turbine.

Current research and development trend of compressed air energy storage

“…When the CAES system is involved in the power system scheduling, sometimes the system can be regarded as generators or the load. Kokaew, Sharkh, and Torbati (2015) studied the performance of a real-time maximum power point tracking algorithm for interference observations of CAES systems, which employed a novel hybrid perturb and observe approach using coarse and fine speed steps to improve the convergence and accuracy of the MPPT. It was found that the method using the rate of change of the power with respect to the speed is better than using the rate of change of the power with respect to the duty cycle of the dc-dc converter.…”

Maximum efficiency point tracking for an ocean thermal energy harvesting system

“…Hence, the method of maximizing the conversion efficiency from mechanical energy to electrical energy is the key point of this research. In power generation fields, the maximum power point tracking (MPPT) technique, which is aimed at capturing the maximum amount of energy from the surroundings, has been widely used and researched . However, for power generation from a stand‐alone energy source, both the duration of generation, which is ignored in MPPT, and the power should be comprehensively considered.…”

“…In power generation fields, the maximum power point tracking (MPPT) technique, which is aimed at capturing the maximum amount of energy from the surroundings, has been widely used and researched. 24,25 However, for power generation from a stand-alone energy source, both the duration of generation, which is ignored in MPPT, and the power should be comprehensively considered. Therefore, for a power generation system whose initial energy is fixed, the most efficient way for energy conversion is the maximum efficiency point tracking (MEPT) technique.…”

Power curves prediction using empirical data regression on small scale compressed air energy storage

“…So the value of specific components of the generator or air motors, such as armature inductance of the generator, armature resistance of the generator, and others must be known before. After that, the values of parameter power curve characteristic of SS-CAES (pressure and speed) entered into the mathematical equation that has been formed from the system, then the operating point of the system can be known [23,24,26]. By reviewing existing research to know the power curve characteristic of the system, they are still using a mathematical model.…”