Enhancement of Voltage Regulation Capability for DC-Microgrid Composed by Battery Test System: A Fractional-Order Virtual Inertia Method

Electric vehicle (EV) has been widely used in our life, one of the key technologies is the batteries, power accumulator battery test system (PABTS), which is initiated for evaluating the performance of the EV batteries, has been used in many battery-manufacture companies. The parallel operation of the PABTS forms a dc-microgrid, owing to the low inertia of the dc-link capacitance, the charging and discharging tests of the batteries can easily cause dc-bus voltage fluctuations, which may jeopardize the system stability. To increase the system inertia and achieve good system stability, a fractional-order model-predictive-control (FOMPC) and fractional-order virtual-inertia-control (FOVIC) strategy (namely, FOMPC-FOVIC method) is proposed for the bidirectional grid-connected converter. First, the fractional-order virtual inertial link is used to replace the integral-order virtual inertial link, which significantly improves the system stability. Second, combined with fractional-order model-predictive-control, virtual dc current compensation is proposed to further suppress the dc-bus voltage fluctuations. Finally, the fractional-order discrete state-space equation of the virtual inertial link is derived, and the cost function design and its optimal solution are elaborated. To demonstrate the effectiveness of the proposed FOMPC-FOVIC scheme, experimental results indicate that the proposed method is superior to the existing methods in terms of inertial support and dc-bus voltage regulation.