Distributed generation system with hybrid inverter interfaces for unbalanced loads

Abstract

Applications of 4-leg inverter are found not only in active and unbalanced load compensators but also as an interface for transferring power generated by renewable energy sources in distributed generation system and microgrids. However existing distributed generation systems commonly use 3-leg inverters. In this paper, the possibility of using a 4-leg inverter interface along with the existing units with 3-leg inverter is explored. This forms the distributed generation system with hybrid inverter interfaces and is studied in detail in presence of unbalanced loads. Analysis of a hybrid system is presented in respect of sequence component analysis of terminal voltages. It is shown that if the expected unbalanced loads are fed from the 4-leg inverter side, the performance of the system is improved in respect of negative and zero sequence components in terminal voltages.

Unbalance mitigation strategies in microgrids

“…Improved virtual power decoupling technique with adaptive adjustment of the compensation is discussed in [148]. The hybrid inverter interface concept is explained in [149], which achieves better VUF if the unbalanced loads are fed by a four-leg inverter than a three-leg one. Souza et al [150] compared three-phase droop and per-phase droop for the performance and stresses on the need to have proper damping in the control.…”

“…The objective of the unbalance compensation or mitigation depends upon the conditions of the MG and the operating mode (islanded or grid‐connected). Unbalance mitigation in islanded MGs [18, 21, 22, 23, 25, 27–32, …”

A Compensation Control Scheme of Voltage Unbalance Using a Combined Three-Phase Inverter in an Islanded Microgrid

“…The microgrid can operate not only in the grid-connected mode, but also in the islanded mode, providing more reliable power to critical loads [4,5]. In the islanded microgrid, most studies focus on parallel-inverter power sharing [6,7] and circulation restraint [8], power management for all kinds of DGs and types of energy storage [9,10], and compensation for voltage unbalance [3,[11][12][13][14][15][16][17][18].…”

“…As for the three-phase four-bridge inverter, the front three bridge legs are used to adjust the positiveand negative-sequence voltages, and the fourth bridge leg is utilized to regulate the zero-sequence output voltage on the basis of the symmetrical component method [16][17][18]. For a three-phase four-leg inverter, the above methods need Clarke transformation, which is used to transform the variables of voltage and current between the abc and αβ frame.…”