Smart Hybrid AC/DC Microgrids

9Unbalanced Voltage Compensation in Smart Hybrid Microgrids

9.1 Introduction

In hybrid AC/DC microgrids, an unbalanced condition is caused by the ever‐increasing unbalanced distribution of single‐phase/unbalanced loads, single‐phase/unbalanced distributed generation (DG), and remote grid faults. The unbalanced voltage has adverse effects on the power system and equipment, including electrical machine overheating, transformer overloading, capacity limitation of power electronics devices, more losses and less stability of the power system, and negative impacts on induction motors and adjustable speed drives. Also, the unbalanced voltage introduces adverse effects on the power electronic converters, such as increased peak current of the converter and double‐frequency power oscillations at the output of three‐phase converters. The power oscillations are also reflected as ripples in the DC link voltage. These adverse effects may lead to instability or system protection if the DC bus voltage exceeds the maximum limit, affecting DC converters and loads in the DC subgrid, and may result in over‐current protection.

In general, the unbalanced voltage can be compensated for by installing additional devices in the power systems, such as a unified power quality conditioner (UPQC), static synchronous compensators (STATCOMs), active power filters, shunt capacitors, to name a few. For detailed information about power quality issues and compensation methods, please refer to Chapter 7. However, ...