MMC Power Conversion Device Independent AC and Capacitor Voltage Control
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Solution Overview
Problem
Existing modular multi-level converter (MMC) systems face difficulties in independently controlling AC power and capacitor voltage, limiting the efficient operation of rotating machines.
Innovation Solution
A power conversion device with a modular multi-level converter (MMC) configuration, utilizing insulated gate bipolar transistors (IGBTs) and a control method that includes a rotating machine target output calculating unit, AC current control unit, and capacitor average voltage control unit, allows for independent control of AC power and capacitor voltage through vector control and pulse width modulation (PWM).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the AC current (active current) in the converter is controlled such that the average voltage of the capacitors of the whole three-phase arms is kept at a rated value, then the capacitor voltage is balanced, but it is difficult to independently control the output of the rotating machine
Solution Approach 1:
The patent segments the control function into two independent parts: (1) AC current control for rotating machine output control, and (2) reactive current control for capacitor voltage balance control. This segmentation allows each control objective to be achieved independently without interference between them.
Solution Approach 2:
The patent introduces reactive current as an intermediary control variable. By controlling the reactive current component separately, the system can adjust capacitor voltages to maintain balance while the AC current component handles the rotating machine output control, thus enabling independent control of both objectives.
2Loss of energy
If a modular multi-level converter is used to reduce power conversion loss, then energy efficiency is improved, but the ability to independently control AC power and capacitor voltage is limited
Solution Approach 1:
The patent changes the control parameters by separating AC current and reactive current as independent control variables. This parameter separation enables the MMC to independently control both AC power output and capacitor voltage, enhancing adaptability while maintaining the low power conversion loss advantage of the MMC structure.
Solution Approach 2:
The patent implements dynamic control where the reactive current is continuously adjusted based on capacitor voltage deviations. This dynamic adjustment mechanism allows the system to adapt to changing operating conditions while maintaining capacitor voltage balance, thus improving versatility without sacrificing energy efficiency.
Data Source
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AI summary
The invention is directed to a power conversion device including a main circuit unit (1) having a plurality of arms to which outputs of a plurality of converters (cells) are connected in series, a driving unit (105) (PWM control unit) which generates a driving signal for driving a plurality of semiconductor switching elements in the main circuit unit (1) according to a voltage command and outputs the signal to the plurality of semiconductor switching elements, an AC control unit (102) (AC current control unit) which generates AC voltage commands for the number of phases on a AC side for controlling AC power of a target to be controlled, and a DC control unit (103) (capacitor average voltage control unit) which generates a DC voltage command for setting an average value of DC voltages of the plurality of capacitors in the main circuit unit (1) to a predetermined value, in which the target to be controlled (rotating machine) is connected to the AC side of the main circuit unit (1), and a voltage command inputted by the driving unit (105) includes the AC voltage command and the DC voltage command.