Alternating current side pre-charging method of modular multilevel converter
A modular multi-level converter technology, applied in the direction of converting AC power input to DC power output, electrical components, output power conversion devices, etc., can solve the problems of large switching loss, poor output characteristics, and high switching frequency , to achieve the effect of protecting safe and stable operation, simple and effective control method, and avoiding impact current
Inactive Publication Date: 2020-10-27
SHANGHAI DIANJI UNIV
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Problems solved by technology
[0003] At present, most of the actual projects are two-level and three-level converters. These two converters are limited by the topology structure, have poor output characteristics, high harmonic content, relatively large switching loss, and high switching frequency. Due to the limitation of switch withstand voltage, these topologies require the use of a large number of switching devices directly connected in series, which has high requirements for the synchronization of device turn-on and turn-off
[0004] The existing method is to cut off the current-limiting resistor on the AC side after the sub-module capacitor voltage meets the minimum voltage required by the sub-module control power supply, and the MMC switches to the controller function during steady-state operation to continue charging the capacitor. Direct use of constant DC control will generate inrush current, which poses a threat to the safe and stable operation of the equipment
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[0027] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
[0028] This application proposes a method for precharging the AC side of a modular multilevel converter. A modular multilevel converter (MMC) is composed of multiple cascaded sub-modules with the same structure. The method includes uncontrolled charging and possible charging. Control the two charging processes.
[0029] The modular multilevel converter includes six bridge arms. The sub-module includes a capacitor and a first IGBT and a second IGBT with anti-parallel diodes respectively. The first IGBT and the second IGBT in the sub-module cooperate with each other to make the sub-mo...
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The invention relates to an alternating current side pre-charging method of a modular multilevel converter. The modular multilevel converter is formed by cascading a plurality of sub-modules of the same structure. The method comprises an uncontrolled charging process and a controllable charging process. The uncontrolled charging process comprises the steps that when the modular multilevel converter is locked, alternating-current side current charges a capacitor through anti-parallel diodes in the sub-modules; the controllable charging process comprises the steps that after the uncontrolled charging is finished, the modular multilevel converter is unlocked, the sub-modules are enabled to be in a semi-locking state, direct-current voltage control with the fixed rise rate is adopted, and thusthe capacitor voltage reaches a specified value and is kept stable. Compared with the prior art, the direct-current voltage control with the fixed rise rate is used in the modular multilevel converter, the control method is simple and effective, the impact current generated by the AC-to-DC control can be avoided, and the safe and stable operation of modular multilevel converter equipment is protected.
Description
technical field [0001] The invention relates to the field of modular multilevel converters, in particular to a method for precharging the AC side of a modular multilevel converter. Background technique [0002] As the core device of high-voltage direct current transmission, the voltage source converter is also a research hotspot in the field of power electronics technology application today. The voltage source converter can operate in four quadrants, the active power and reactive power can be independently controlled, and the power flow can be reversed by changing the direction of the current, so the application prospect is very broad. [0003] At present, most of the actual projects are two-level and three-level converters. These two converters are limited by the topology structure, have poor output characteristics, high harmonic content, relatively large switching loss, and high switching frequency. Due to the limitation of switch withstand voltage, these topologies requi...
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IPC IPC(8): H02M7/219H02M1/32
CPCH02M1/32H02M7/219
Inventor 高桂革柳康
Owner SHANGHAI DIANJI UNIV