Dual unipolar voltage module chain and its hybrid multilevel converter

Abstract

The invention provides a dual unipolar voltage module chain and a hybrid multilevel converter, and belongs to the fields of a power electronic technology and power transmission and distribution. The dual unipolar voltage module chain consists of N unipolar voltage modules which are connected in series in sequence, wherein the N unipolar voltage modules comprise N1 positive electrode unipolar voltage modules and N2 negative electrode unipolar voltage modules; when a bidirectional current passes through, bipolar voltage output capability is formed; the hybrid multilevel converter based on the module chain at least comprises two same phases, wherein each phase comprises a dual unipolar voltage module chain, a three-level bridge arm and an electric reactor, wherein one port of the dual unipolar voltage module chain is connected with the midpoint of the three-level bridge arm while the other port of the dual unipolar voltage module chain is connected with one end of the electric reactor; and the other end of the electric reactor is connected with an alternating current voltage. By adoption of the dual unipolar voltage module chain and the hybrid multilevel converter, wide-range alternating current-direct current conversion can be realized at a relatively low engineering cost and in a compact occupied space; and meanwhile, high conversion efficiency, good harmonic characteristic and direct current fault ride-through capability are achieved.

Description

Technical field [0001] The invention belongs to the fields of power electronic technology and power transmission and distribution, and particularly relates to a dual unipolar voltage module chain and a hybrid multilevel converter thereof. Background technique [0002] Traditional two-level and three-level converters used in flexible DC transmission, motor drive and other fields often adopt two-phase or three-phase structure to achieve AC-DC power conversion; in high-voltage applications, they will be combined with full control switches The series technology of devices (typically insulated gate bipolar transistors, IGBTs) constitutes a high-voltage two-level or high-voltage three-level converter. The main problem of this type of converter is that due to the small number of levels, in order to obtain better output harmonic characteristics, the switching frequency needs to be greatly increased, but it also brings the disadvantage of a sharp increase in switching losses, which limits...

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Problems solved by technology

However, the common problem of unipolar voltage modules is that they do not have zero and positive and negative bipolar voltage output capabilities in the bidirectional current operating range, and only have zero and positive and negative bipolar voltage output capabilities in a single current direction. Through the opposite current direction, only zero and positive polarity or zero and negative polarity unipolar voltage output capability; in other words, the unipolar voltage module only has zero and positive polarity or zero and negative polarity unipolar voltage output capability in the operating range of flowing bidirectional current pole voltage output capability

Therefore, the operating range of the current module chain composed of unipolar voltage modules is also limited by this. The unipolar voltage module chain is only used in the bridge arm of the MMC based on the first type of technology, that is, using multiple identical unipolar The voltage modules are connected in series to form a unipolar voltage module chain, and control the on and off states of each fully-controlled switching device in the module, so that each unipolar voltage module only outputs zero and positive polarity voltages in the bidirectional current operating range

[0012] Therefore, the connection structure and control method of the traditional unipolar voltage module chain do not have the ability to output positive and negative bipolar voltage in the bidirectional current operating range, so it cannot be used in HCMC or HNMC to replace the full control switch Higher component count, more expensive chain of full-bridge modules

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