A comparative study of Droop Compensation Functions for State-of-Charge based adaptive droop control for Distributed Energy Storage Systems

DC microgrid applications normally use Distributed Energy Storage Systems (DESS) to smooth out energy balance due to the non-dispatchable characteristics of renewable resources. Since the State of Charge (SoC) of each energy storage unit (ESU) can differ significantly SoC based adaptive droop control methods for SoC equalization has been proposed in literature. A droop compensation function is used to vary the DESS converter droop resistance according to each storage unit SoC, which promotes gradual SoC equalization and power sharing. In previous works power and exponential functions have been used to implement the droop compensation, however, no information can be found regarding the performance of other mathematical functions on DESS SoC balancing. This paper investigates the employment of a set of basic mathematical functions in SoC based adaptive droop control and discusses the influence of tuning parameters on equalization speed and voltage deviation.

I. Introduction

Typical dc microgrids are described as small distribution power systems which employ renewable distributed generation and power management to supply a set of local loads and that can operate connected to or isolated from the utility grid. Due to the intermittent nature of the renewable resources, distributed energy storage units (DESU) are used to smooth out energy balance [1]. A typical configuration of a dc microgrid is shown in Fig. 1, which a Bidirectional Grid Interface Converter (BGIC) is used to connect the dc microgrid to the utility grid. Renewable generation is represented by a photovoltaic (PV) array and a wind turbine. The energy storage system is accomplished with distributed ESUs. Fig. 1.

Typical configuration of a dc microgrid