Analysis of variable pulse width modulation of air volume on efficiency and power controllability of micro-compressed air energy storage

The transition to an energy system that integrates 100% variable renewable energy (VRE) requires the development of energy storage technologies at micro and small scales. One promising technology at the micro-scale is the compressed air energy storage (CAES) system. However, the current state of knowledge indicates low round-trip efficiency (RTE) as the main barrier. One of the main causes is pressure fluctuations during the discharge process. Current methods for discharging air mass reservoirs rely on an isochoric approach with high-loss throttling valves or a complex isobaric approach. This paper introduces a novel control approach based on pulse-width modulation (PWM), which removes the need for throttling elements and allows for stable and high-efficient power output during the isochoric tank discharge. As part of the research, a power relationship was developed to connect tank pressure with the cut-off ratio. Computer simulations confirmed that this approach enables stable 5 kW power generation with over 72% discharge exergy efficiency and introduces wide-range controllability, allowing the output power to be flexibly adjusted between 2.5 and 7.5 kW while maintaining high efficiency. The proposed discharge strategy shows promise for achieving deep tank discharge with high process efficiency and wide control over output power.