Abstract

A battery energy storage system (BESS) was conceived to reduce fuel consumption and maintenance costs of diesel-hybrid mini-grids [1]. It operates in 2 different modes. In the genset support mode, it balances the load and maintains a unity PF for genset, and it supplies/absorbs power to force the genset to operate with higher efficiency, less mechanical vibrations and less risk of carbon build-up. In the grid forming mode, it provides a balanced voltage to the highly unbalanced load, common in small autonomous power systems. In this Thesis, this theoretical study is taken to the next level by implementing it in the laboratory to assess its performance.
This system was so far tested theoretically by simulations, probably with ideal conditions. In this Thesis, after carefully studying the system, some modifications are brought into it, considering the real time challenges of test bench. The first modification is the implementation of a phase lock loop (PLL), considering the voltage unbalance issue, which is likely to occur at the point of common coupling (PCC) due to the highly unbalanced loads. The second modification is the implementation of the proposed per-phase synchronizer, which is required to change the mode of operation from one to another, instead of the formerly employed Intelligent Connection Agent (ICA), making the system simpler to implement. The final modification is in the MSTS block (Mode Selection and Transition System) to bring intentional and unintentional change in the mode of operation, additional features.
After applying the above said modifications to the BESS system, it was tested in the laboratory to see if it meets the design specifications, where the control was implemented on a programmable inverter called Triphase® inverter system, and a power supply known as Ametek® (California Instruments) was working as a genset. The battery of the BESS was emulated, a contribution of Thesis, by a diode rectifier connected to Concordia’s grid and a controllable bleeding resistor so that the emulated battery can supply and absorb active power to the AC grid.
Based on the experimental evidences, it is concluded that this BESS system is highly suitable for genset support mode, grid forming mode and while changing the mode from one to another.