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A Nearest Level Approximation Modulation Method Based on Common Mode Injection for MMC

A recent technology of level approximation and modulation method, applied in the direction of converting irreversible AC power input to DC power output, etc., can solve difficult and costly problems, achieve reasonable total loss, optimize total loss, and reduce conduction loss Effect

Active Publication Date: 2017-05-24
ZHEJIANG UNIV
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Problems solved by technology

The former requires device optimization in terms of conduction voltage drop, switching time, etc., and hardware upgrades, so it is more difficult and costly

Method used

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  • A Nearest Level Approximation Modulation Method Based on Common Mode Injection for MMC
  • A Nearest Level Approximation Modulation Method Based on Common Mode Injection for MMC
  • A Nearest Level Approximation Modulation Method Based on Common Mode Injection for MMC

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Embodiment Construction

[0032] In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0033] Such as figure 1 As shown, the basic unit of a single-ended three-phase modular multilevel converter (MMC) is a sub-module (Sub-Module, SM). N sub-modules are cascaded and a bridge arm inductor is connected in series to form a bridge arm. The bridge arms are connected in series to form a phase unit. The three-phase MMC converter contains three phase units, six bridge arms, and 6N sub-modules. DC side bus voltage is U dc , the three-phase phase voltages on the AC side are respectively u a , u b and u c . Point O is the zero potential reference point.

[0034] The modulation method of the MMC converter is derived from the PWM modulation method of the multi-level converter. MMC also has the characteristics of a large number of levels. In actual...

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Abstract

The invention discloses a common-mode-injection-based nearest level modulation method for a modular multilevel converter (MMC). According to the method, a common-mode component is injected into a three-phase nearest level modulation wave and the phase voltage magnitude level is reduced based on topping introduced by the common-mode injection, so that the number of sub modules needed by the bridge arm can be effectively reduced under the circumstances that the voltages of the sub modules are not changed; and in order to guarantee the unchanged voltage level of the direct current side, at least one invested sub module exists in the bridge arm at each moment after common-mode injection introduction. Moreover, because the same three-phase common-mode components, the wire voltage level of the three-phase system after injection is not changed. Therefore, under the circumstances that the power transmission level is not changed, the number of sub modules needed by the MMC can be effectively reduced, thereby reducing the MMC conduction losses at the same current level and realizing reasonable optimization of the total losses of the MMC system.

Description

technical field [0001] The invention belongs to the technical field of power electronic control, and in particular relates to a common-mode injection-based nearest level approximation modulation method suitable for MMC. Background technique [0002] Since the advent of Modular Multilevel Converter (MMC) in 2002, it has increasingly become a high-voltage DC (High-voltage DC) One of the most promising converter topologies in Voltage Direct Current (HVDC) transmission systems. [0003] Benefiting from the low switching frequency, the switching loss of the MMC system is relatively low; however, in order to ensure the quality of the output waveform on the AC side, the MMC needs to contain a large number of sub-modules. Due to this limitation, its loss is higher than that of the traditional multi-level topology. The increase in loss not only increases the difficulty of heat dissipation design, but also puts forward higher requirements for the stress of switching devices. Therefo...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02M7/19
Inventor 李武华周维浩顾云杰董玉斐何湘宁
Owner ZHEJIANG UNIV
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