Voltage balance strategy of T-type AC-DC-AC nine-level converter

Abstract

The invention discloses a voltage balance strategy of a T-type AC-DC-AC nine-level converter, and belongs to the technical field of control of power electronic converters. The control strategy comprises rectification side DC voltage outer loop control and inductive current inner and inversion side amplitude single closed loop control. Therefore, grid-side unity power factor operation is realized, and direct-current side voltage and output voltage are stable and controllable. The voltage balance strategy can realize balance of direct current side voltage among modules and capacitor voltage in the modules, so that smooth nine-level step waves are output at an alternating current side. According to the voltage balance strategy of the T-type AC-DC-AC nine-level converter of the invention, a high-quality voltage source can be provided for various alternating-current loads which are not more than 50kW at most, high-level output can be realized, a medium-voltage power distribution network can be accessed without an industrial frequency transformer, and the quality of grid-connected current and output voltage can be ensured by using relatively small filter inductance. The voltage balance strategy of the invention can be applied to occasions with higher voltage level and higher power.

Description

technical field [0001] The invention belongs to the field of power electronic converters, and in particular relates to a voltage balance strategy of a T-type AC-DC-AC nine-level converter. Background technique [0002] Single-phase AC-DC-AC converters have been used in many applications, such as uninterruptible power supplies, unified power quality regulators, AC voltage regulators, (High-performance online UPS using three-leg- type converter[J].IEEE Transactions on Industrial Electronics,2005,52(3):889-897.) discloses a three-arm topology shared by the bridge arms, which not only saves costs compared to the traditional double H-bridge topology , and the loss is also lower. In traditional two-level or three-level AC-DC converters, the output voltage and grid-side current contain more harmonic components, and there is a phase difference between the grid-side current and grid voltage, making it difficult to achieve grid-side unit power factor operation. Compared with the tra...

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Problems solved by technology

However, the improvement of the withstand voltage of the switching tube makes it have higher switching loss, so the T-type three-level is only suitable for medium and low voltage applications (Design and Implementation of a Highly Efficient Three-Level T-Type Converter for Low-Voltage Applications[J ].IEEE Transactions on Power Electronics,2013,28(2):899-907.)

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