Since the proposed voltage compensation term guarantees autonomous bus voltage restoration, the supercapacitor state of charge (SoC) remains at nominal value without violation while it only buffers fluctuating power. However, the battery only compensates for the nominal power demand.
The DC bus voltage, battery charging cycle, and supercapacitor SoC restoration are improved significantly with the proposed voltage compensation mechanism. Fig. 13. Comparison of charging and discharging cycle for the battery. Fig. 14.
In LV grids, due to the increasing share of sizeable single-phase loads, voltage unbalance also has to be addressed. Unbalance compensation may be achieved by reactive power control and optionally active power curtailment of single-phase inverters [ 27, 28 ].
It is a challenge to develop an effective voltage-regulation method using a straightforward implementation. This paper proposes a novel method for local voltage control and balancing using a shunt-connected energy storage system. The compensation principles are explained, and a complete controller design is proposed.
The compensator is a 3-phase Voltage Source Inverter (VSI) equipped with any type of energy storage on the DC side. It can provide flexible active and reactive current injection to the grid and is represented by a controlled current source Ic. Together with the load Z, it is connected at the Point of Common Coupling (PCC). Figure 1.
The nominal SoC of the supercapacitor is set to 0.5. Due to the DC bus voltage deviation, the conventional approach is unable to restore the nominal SoC throughout the entire simulation time. However, the proposed voltage compensation mechanism is capable to restore the nominal SoC of the supercapacitor.