Voltage Regulation and Load Sharing in DC Microgrid Using Single Variable Global Average Estimation

This article proposes a distributed secondary controller for dc microgrid which achieves both current sharing and voltage regulation by exchanging just one variable per converter. Generally, output current and voltage information are used by secondary controllers to attain both these objectives. With more sources, the amount of data to be handled, and thus, the bandwidth required by the communication network, is more. On the contrary, in the proposed controller, an intermediate variable, which is the combination of per-unit current and voltage measurements, is generated. The global average estimate of this intermediate variable, evaluated through consensus protocol, is communicated among neighboring controllers. The secondary control action is to add a voltage shift to the reference voltage, ultimately achieving both control objectives. The steady-state operating condition of the proposed controller is derived, and the stability of the dc microgrid is analyzed by tracing the dominant poles of the system. The operation of the proposed controller is verified with the MATLAB/Simulink platform and through experiments on a dc microgrid laboratory prototype. The proposed controller shows better performance compared to other single variable communication-based secondary controllers.

I. Introduction

The dc nature of renewable energy sources, energy storage units, and electronic loads has increased the popularity of dc microgrids. These sources, storage devices, and loads are connected to the dc bus using appropriate power electronic converters (PECs) [1]. Conventionally I-V droop characteristics are implemented in the energy storage units of the microgrid to achieve the proportional current sharing [2]. However, its performance is affected by unequal line/cable resistances connecting the PECs with the dc bus [3]. Also, the implementation of decentralized droop control results in poor voltage regulation of the dc bus. Moreover, as the control action is based on local information, precise proportional current sharing cannot be achieved globally with the primary controller. To address these issues, secondary controllers are used along with the primary droop controllers [4].