A cascaded step-up unidirectional DC transformer

Abstract

The invention discloses a unidirectional direct current voltage transformer which comprises a voltage source type current converter, an uncontrollable rectifier, and an inductor-capacitor voltage step-up loop circuit, wherein positive and negative electrodes of the voltage source type current converter are respectively connected with positive and negative electrodes of a low voltage direct current system; positive and negative electrodes of the uncontrollable rectifier are respectively connected with positive and negative electrodes of a high voltage direct current system; an alternating current side of the voltage source type current converter is connected with one end of an alternating current inductor, the other end of the alternating current inductor is connected with one end of an alternating current capacitor, the other end of the alternating current inductor is also connected with an alternating current side of the uncontrollable rectifier via an alternating current voltage transformer, and the other end of the alternating current capacitor is grounded. According to the converter in the invention, technologies of realizing two stage voltage step-up via the inductor-capacitor and the alternating current voltage transformer are adopted, the quantity of used power modules can be greatly reduced, and difficulty of controlling voltage sharing and current sharing among all power modules can be lowered.

Description

technical field [0001] The invention belongs to the technical field of electric power transmission and distribution, and more specifically relates to a cascaded step-up unidirectional DC transformer, which is used to unidirectionally transmit DC power from a low-voltage DC system to a high-voltage DC system to achieve a high step-up ratio . Background technique [0002] High transformation ratio DC transformer is the key equipment in DC distribution network, photovoltaic DC grid-connected system, and wind power DC grid-connected system. It is used to realize the power interconnection between low-voltage DC system and high-voltage DC system, and its transformation ratio can be as high as 20- 40. High-power DC transformers usually use DC-AC-DC conversion technology to realize bidirectional power transmission between two DC grids. The converters used are voltage source converters, which bring high costs and high losses. the price. [0003] In some typical applications, such ...

AI Technical Summary

Problems solved by technology

However, when a large number of DC-AC-DC transformer power units are used in series and parallel, it will bring about the problem of voltage and current sharing among the power units, and it will also bring great difficulties to the development of the control system. The total cost, but also greatly reduces the reliability of the system, this type of modular series-parallel structure still needs to put all the power units into operation at low load, making the efficiency low at low load

[0005] Although it is possible to use an inductance-capacitance-inductance step-up DC-AC-DC transformer without galvanic isolation for the internal AC circuit, such as the document "LCL DC / DC converter for DC grids" (Dragan Jovcic, Lu Zhang, IEEE Transactions on Power Delivery, 2013, 28(4), 2071-2079) disclosed a capacitor-inductor-capacitor step-up DC-AC-DC transformer, whose typical transformation ratio is higher than that of high-frequency transformers, but only relies on Inductor-capacitor-inductor boost, the highest boost ratio is generally 5, and it is still difficult to achieve a transformation ratio of 20-40

Moreover, because the DC systems on both sides of this type of topology can only use symmetrical bipolar topology, it cannot be used to connect unipolar DC systems, and this type of topology cannot be used as a basic power unit for modular series-parallel combination, making it difficult to further improve its step-up ratio, and it is for bi-directional power transfer, cost-inefficient for uni-directional power transfer applications

[0006] In summary, the existing high-power and high-voltage DC-AC-DC transformers have the defects of complex system structure and control, low power unit conversion ratio, and low operating efficiency under low-load conditions.

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