Multiport DC/DC system (MDS with stepless DC voltage regulation

Abstract

The invention provides a multiport DC / DC system (MDS) topology with stepless DC voltage regulation. The MDS has multiple ports to be interconnected with an external DC system. The ports are configured as a hybrid series converter. An AC side is connected to a common AC bus in the MDS through an AC circuit breaker. In the MDS, transformers match DC lines with different voltage classes. The hybrid series converter is formed by connecting in series a current-source converter unit and a voltage-source converter unit. The current-source converter unit includes a LCC based on a diode or a thyristor. The voltage-source converter unit has a modular multi-level structure. Each bridge arm is formed by cascaded connection of sub-modules with no negative level output capabilities (such as IGBT module, HBSM) and sub-modules with negative level output capabilities (such as FBSM). The MDS has a stepless DC voltage regulation (or even reverse polarity) capability, achieves both DC fault ride through and rapid recovery capabilities, helps to quickly reverse power flow. Therefore, the MDS topology helps to promote the application of the multi-port DC-DC converter in a DC power system.

Description

technical field [0001] The invention relates to a device in the technical field of power transmission and distribution, in particular to a multi-port DC-DC voltage transformation system with stepless regulation of DC voltage. Background technique [0002] With more and more new energy sources such as wind power and solar power connected to the grid and the development of DC transmission technology, a multi-terminal DC transmission technology has been formed on the basis of point-to-point HVDC technology, and has further developed into a DC grid. A technology that directly constitutes a DC grid is to interconnect multiple DC lines on the DC side. However, due to the immature technology of DC circuit breakers and DC grid protection, this DC grid technology faces many challenges and technical difficulties, mainly as follows: 1 ) It is impossible to interconnect DC lines with different voltage levels; 2) It is weak to deal with DC faults. A DC fault at any point in the DC grid w...

AI Technical Summary

Problems solved by technology

At present, there are existing literatures to carry out research on DC / DC converters, such as using chopper circuits for low-voltage applications, but if they are applied to the field of DC transmission, multiple IGBTs need to be directly connected in series, which is technically difficult; another example is the use of three-phase Active bridge (Dual-active-bridge, DAB) technology constructs DC-DC converters. The advantage of this technology is that it can reduce the size when operating at high frequency, and the loss is relatively small. However, in the field of DC power transmission, especially onshore DC power transmission Pay attention to the operation loss of the whole system. Whether this technology is suitable for onshore DC power transmission needs to be verified; another example is the use of multi-port DC-DC conversion technology based on inductance-capacitance-inductance circuits. One of the main starting points of this technology is to save transformers and Reduce the platform area, so that it can be easily applied to offshore DC transmission. Similarly, whether this technology is suitable for land DC transmission is also open to question

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