Improved modulation method based on NLM and PWM hybrid modulation

A technique of modulation method and sorting algorithm, which is applied to output power conversion devices, electrical components, and conversion of AC power input to DC power output, etc., which can solve the problem of reducing the harmonic distortion rate of output voltage and current, and poor quality of voltage and current waveforms, etc. problem, to achieve the effect of reducing harmonic distortion rate, simple control and easy realization

Pending Publication Date: 2020-11-17
SHANGHAI JIAO TONG UNIV
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  • Abstract
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Problems solved by technology

[0005] The present invention aims at the problem that the output voltage and current waveform quality of the existing NLM and PWM mixed modulation strategy is poor under medium and low cascade number sub-modules, and proposes an improved modulation method based on NLM and PWM mixed modulation, so that each With limited n sub-modules and without changing the average voltage of the sub-module capacitors and increasing the carrier frequency, the bridge arm doubles the level of the output voltage, which can overcome the disadvantage of a small number of medium-voltage MMC modules. The harmonic distortion rate of the output voltage and current can be significantly reduced under the medium and low cascade number sub-modules

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  • Improved modulation method based on NLM and PWM hybrid modulation
  • Improved modulation method based on NLM and PWM hybrid modulation
  • Improved modulation method based on NLM and PWM hybrid modulation

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Embodiment Construction

[0031] Such as figure 1 As shown, the modular multilevel converter (MMC) involved in this embodiment is composed of three-phase six bridge arms, and each bridge arm is composed of n half-bridge sub-modules and 1 circulating current suppression reactor L is formed in series, and each sub-module includes: two fully-controlled switch tubes V1, V2 and their anti-parallel diodes D1, D2, and a voltage stabilizing capacitor C.

[0032] The sub-modules have two levels of +E, 0 (E is the average value of the capacitance voltage of each sub-module), and the working modes of each sub-module include:

[0033] 1) V1 is turned off and V2 is turned on;

[0034] 2) V2 is turned off and V1 is turned on;

[0035] 3) PWM mode.

[0036] Such as figure 2 As shown, is a schematic diagram of the hybrid modulation process involved in this embodiment. For MMC, the output voltage of the AC side is the superposition of the output voltages of the upper and lower bridge arms. When the hybrid modulat...

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Abstract

The invention discloses an improved modulation method based on NLM and PWM hybrid modulation, and the method is characterized in that the method achieves the voltage sharing of the capacitor voltage of a sub-module through employing a sorting algorithm for n-1 sub-modules of a modular multilevel converter, so as to achieve the optimal approximation to a fundamental wave; meanwhile, a sub-module isintroduced into each of the upper bridge arm and the lower bridge arm of the MMC to work in a high-frequency PWM mode, and the PWM carriers of the upper bridge arm and the lower bridge arm adopt thesame carrier. According to the invention, the harmonic distortion rate of the output phase voltage and phase current can be significantly reduced, the output electric energy quality is higher, the complex carrier generation and additional closed-loop voltage balance control are not needed, and the method has the advantages of simple control, low cost and easy realization.

Description

technical field [0001] The invention relates to a technology applied in the field of medium-voltage large-capacity converters, in particular to an improved modulation method based on hybrid modulation of Nearest Level Approximation Modulation (NLM) and Pulse Width Modulation (PWM). Background technique [0002] As a new type of multilevel topology, modular multilevel converter (MMC) has a series of advantages such as high modularity, good redundancy, high efficiency, and convenient capacity increase. In medium-voltage and large-capacity converters, such as medium-voltage motor drive, new energy power generation grid connection; static synchronous reactive power compensation device and other fields, it has shown wider application value and better development prospects. [0003] The ideal modulation method of a modular multilevel converter (MMC) should satisfy: the harmonic distortion rate of the modulated output waveform is as low as possible; for switching devices, the switc...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02M7/483H02M7/5387H02M7/5395H02M1/12
CPCH02M1/12H02M7/483H02M7/53875H02M7/5395H02M7/4835
Inventor 姚钢周荔丹
Owner SHANGHAI JIAO TONG UNIV
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