AC-AC stage modulation method for three-stage modular power electronic transformer

Abstract

The invention discloses a Three-stage modular power electronic transformer AC-AC transform level modulation method, and belongs to the technical field of power electronics. Firstly, the sub-modules are divided into two groups. One group uses the CPS-SPWM to output low frequency alternating current and another group outputs high frequency rectangular wave directly. The voltage of the sub-module isdetected in time, and the charge and discharge of the sub-module is balanced according to the working state of voltage high-low exchange. By using different sub-modules to output high frequency rectangular wave and low frequency alternating current, the rectangular wave can be generated accurately, which is beneficial to reduce the bridge arm current. When the sub-module outputs high frequency rectangular wave, the switching frequency is the same as the fundamental frequency of the rectangular wave, which can greatly reduce the switching frequency. The modulation also has the function of voltage equalization of the sub-module. The modulation method of the invention is beneficial to improving the efficiency and power density of the three-stage modular power electronic transformer, and reducing the cost and engineering difficulty thereof.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a three-stage modularized power electronic transformer AC-AC step modulation method. Background technique [0002] The three-stage modular power electronic transformer consists of an input stage modular AC-AC converter, a high frequency isolation stage DC-DC converter and an output stage DC-AC converter. The use of the AC-AC converter reduces the power electronics The number of transformation stages of the transformer makes the three-stage modular power electronic transformer have the advantages of fewer sub-modules, IGBTs and high-frequency transformers than the four-stage modular power electronic transformer that has been widely studied at present, and has a good application prospect. However, the modular AC-AC converter needs to output low-frequency (power frequency) AC and high-frequency AC / rectangular wave at the same time. The existing modulation stra...

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Problems solved by technology

However, the modular AC-AC converter needs to output low-frequency (power frequency) AC and high-frequency AC / rectangular wave at the same time. The existing modulation strategies that can realize the above functions mainly include Nearest Level Approximation Modulation (NLM) and carrier phase shifting. Sinusoidal Pulse Width Modulation (CPS-SPWM): NLM requires a large number of sub-modules and is suitable for high-voltage applications; CPS-SPWM usually requires a carrier that is 8 times higher than the frequency of the modulating wave, resulting in too high a switching frequency, difficulty in device selection, and loss Large, and because the rectangular modulation wave contains high-frequency components, it is difficult to accurately restore it through CPS-SPWM

For medium-voltage distribution network occasions where power electronic transformers are extensively studied at this stage, the number of sub-modules of power electronic transformers is not too large, so NLM is not applicable, and CPS-SPWM is also difficult to do due to its high switching frequency, which affects the three-level Development and Application of Type Power Electronic Transformer

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