Abstract
Owing to the necessity of the transformer for the multi-parallel inverters connected to the medium-voltage (MV) grid, the conventional multi-parallel inverter topology can be reconfigured to the dual-inverter fed open-end winding transformer (DI-OEWT) topology to obtain lower output voltage harmonics, which can reduce the requirement of the filter inductance. However, due to the special structure of the DI-OEWT topology, the arrangement scheme of the filter can be more than one kind, and different schemes may affect the filter performance. In this paper, research on the existing two kinds of filters, as well as a proposed one, for the DI-OEWT topology used in photovoltaic grid-tied applications is presented. The equivalent circuits of these filters are derived, and based on this, the harmonic suppression capability of these filters is analyzed and compared. Furthermore, a brief parameter design method of these filters is also introduced, and based on the design examples, the inductance and capacitance requirements of these filters are compared. In addition, these filters are also evaluated in terms of the applicability for fault tolerance. At last, the analysis is verified through an experiment on a 30 kW dual-three-level inverter prototype.
Highlights
In recent years, the increasing exhaustion of traditional fossil energy has resulted in an emerging interest in the development of renewable energies, one of which is solar energy that has already obtained widespread applications
Since the transformer is essential for the inverters connected to the MV grid, the multi-parallel inverter topology has the possibility to be reconfigured to the dual-inverter fed open-end winding transformer topology
This paper investigates the filters for the dual-inverter fed open-end winding transformer (DI-OEWT) topology used in the photovoltaic grid-tied applications
Summary
The increasing exhaustion of traditional fossil energy has resulted in an emerging interest in the development of renewable energies, one of which is solar energy that has already obtained widespread applications. Among all types of commercial solar energy applications, photovoltaic grid-tied system plays an important role, and large-scale photovoltaic power plants have become dominant [1]. In the large-scale photovoltaic power plants, three-phase single-stage central inverters are widely used because of their many advantages, such as cost-effectiveness, simplicity in hardware design and easy maintenance. Voltage source inverters (VSI) are the most widely used topologies among the current commercial central inverters [2]. Multi-parallel inverter topology, in which the inverters are connected in parallel through step-up MV transformers, are commonly used in these systems. A typical commercial application example is 1 MW MV turnkey station, which is composed of two 500 kW central inverters and one 1 MVA MV transformer [3]. Since the transformer is essential for the inverters connected to the MV grid, the multi-parallel inverter topology has the possibility to be reconfigured to the dual-inverter fed open-end winding transformer (denominated here as DI-OEWT) topology
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