High-capacity unified power quality conditioner based on chain structure and control method thereof

Abstract

The invention relates to a high-capacity unified power quality conditioner based on a chain structure and a control method of the high-capacity unified power quality conditioner. A three-phase three-wire system series-and-parallel structure is adopted in the high-capacity unified power quality conditioner. The high-capacity unified power quality conditioner comprises a series type voltage source converter and a parallel type voltage source converter, wherein the series type voltage source converter and the parallel type voltage source converter are connected through a common direct-current bus, single-phase H-bridge cascade structures are adopted in the series type voltage source converter, the H-bridge cascade structure of each phase is connected to an alternating-current side power grid through a series capacitor, single-phase H-bridge chain link structures are adopted in the parallel side converter, a back-to-back structure is formed by the single-phase H-bridge chain link structures and H-bridge chain links of the series type voltage source converter, and each H-bridge chain link of the parallel side converter is connected to a direct-current side power grid through the secondary side of a single-phase multi-winding transformer. The invention further provides the control method of the high-capacity unified power quality conditioner. According to the high-capacity unified power quality conditioner, a series side transformer is omitted, short-circuit impedance of a loop is reduced, voltage accuracy of open-loop control is improved, performance of the high-capacity unified power quality conditioner is improved, and the problem that the instantaneous inrush current phenomenon happens when voltage drop of the series side happens is solved.

Description

technical field [0001] The invention relates to a unified power quality controller (UPQC-Unified Power Quality Conditioner) and a control method thereof, in particular to a large-capacity unified power quality conditioner based on a chain structure and a control method thereof. Background technique [0002] The unified power quality controller (UPQC-Unified Power Quality Conditioner) is composed of a series voltage source converter and a parallel voltage source converter through a common DC bus. It is applied to the power distribution system and connected near the harmonic load. Both voltage and current can be compensated simultaneously. The series converter plays the role of a dynamic voltage compensator (DVR-Dynamic Voltage Restorer), which can suppress voltage fluctuations, compensate power supply voltage harmonics, eliminate voltage swells and voltage temporary problems that often occur in power distribution systems, and improve System damping. The parallel-connected c...

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Problems solved by technology

[0004] The UPQC capacity of the three-phase three-wire structure is small, which does not meet the large-capacity compensation needs of industrial users

And because the three-phase output voltages of the three-phase bridge are related to each other, the control is more complicated, and the zero-sequence voltage cannot be provided to the system; while the three-phase four-wire structure can compensate the zero-sequence, but it has high requirements for the output voltage of the DC side, and the switching device The withstand voltage value is high, and the capacitor voltage on the DC side is prone to imbalance

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