Cascaded multilevel converter with interconnected single-phase direct-current ports

Abstract

The invention provides a cascaded multilevel converter with interconnected single-phase direct-current ports. The cascaded multilevel converter comprises a first single-phase double-winding transformer, two cascaded multilevel voltage source type converter sets and a reactor set located on the alternating-current side of any one or two converter sets. Each cascaded multilevel voltage source type converter set comprises a plurality of single-phase voltage source converters, the alternating current side of the first cascaded multilevel voltage source type converter set is connected to a single-phase power grid power supply through a first single-phase double-winding transformer, and the alternating current side of the second cascaded multilevel voltage source type converter set is connectedto another single-phase power grid power supply. And a direct-current filter bank is also arranged between the direct-current sides of the two cascaded multilevel voltage source type converter banks.And a second single-phase double-winding transformer or an alternating-current filter is arranged on the alternating-current side of the second cascaded multilevel voltage source type converter groupand is used for supplying power to the single-phase passive power grid. The cascaded multilevel converter has the advantages of good harmonic characteristics of alternating current ports on two sides,high operating efficiency in a full-load range, low loss, high reliability in fault locking and redundant operation and the like.

Description

technical field [0001] The invention relates to a cascaded multilevel converter in a traction power supply system, in particular to a cascaded multilevel converter interconnected with single-phase DC ports. Background technique [0002] In the traction power supply system, the unbalanced three-phase voltage, harmonics and low power factor caused by the asymmetrical load in the traction substation. At the same time, in traction substations and districts, there are electric phase-splitting and no-electric areas, which affect the continuous and reliable flow of electric locomotives, limit the average speed of locomotives, and seriously cause driving accidents such as arcing and locomotives. [0003] Using cascaded multilevel converters interconnected with large-capacity single-phase DC ports, comprehensive compensation for negative sequence, reactive power and harmonics can be realized on the traction side of the traction substation. At the same time, installing one or more ca...

AI Technical Summary

Problems solved by technology

[0006] Invention patent ZL200710175253.2 The use of single-phase multi-winding transformers on one side brings the following disadvantages: 1) The processing technology of single-phase multi-winding transformers is relatively complicated, the volume and weight are too large, the manufacturing cost is high, and the leakage reactance of the split transformer is relatively large Reduce the capacity utilization of the converter; 2) In order to obtain relatively good harmonic characteristics at the primary port of the single-phase multi-winding transformer, it is necessary to carry out phase shift control between the windings of each secondary side, thereby forming a large The characteristic sub-harmonic circulating current increases the operating loss and further reduces the capacity utilization of the power electronic converter connected to the secondary side

However, multiple transformers in series introduce new problems: 1) Due to the inherent differences in the excitation reactance of each transformer, when the equipment fails, when the load operation enters the pulse blocking state, the induced voltage difference of the secondary windings of each transformer is relatively large. Large, it may cause the DC voltage of each secondary side converter to be inconsistent, and in severe cases, the equipment will be damaged by overvoltage

In order to suppress the inconsistency of this transformer, it is necessary to adopt an additional damping circuit, which increases the complexity and cost of the circuit, and reduces the operating efficiency

2) The total number of secondary windings of the series multiple transformer group has not been substantially reduced, and is still the same as the total number of power units on the side of the converter, and the manufacturing cost and maintenance cost of the multiple transformer group are still high

When the N-1 or even N-2 units of the equipment fail redundantly, it will further increase the difficulty of the control and protection cooperation between the transformer and the converter power unit, and reduce the operation reliability.

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