Hybrid-Current-Mode Control for MMC Capacitor Voltage Ripple
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Solution Overview
Problem
Modular multilevel converters (MMCs) face challenges in minimizing capacitor voltage ripple in switching power cells, particularly in high-voltage, high-power applications, where conventional methods are unsuitable due to high power device losses and increased volume and cost with large capacitance.
Innovation Solution
The implementation of a hybrid-current-mode (HCM) switching-cycle control (SCC) technique that selectively uses peak current mode and average current mode for different arms of the MMC, allowing for independent control of switch control signals to reduce capacitor voltage ripple, utilizing controllers to manage switch states and minimize shoot-through states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional control methods are used to minimize capacitor voltage ripple, then voltage ripple is reduced, but power device losses increase significantly in high-voltage, high-power applications
Solution Approach 1:
The patent applies different control strategies to different arms of the MMC based on local conditions. Specifically, it uses hybrid current mode control for arms with larger current ripple and average current mode control for arms with smaller current ripple, optimizing the balance between voltage ripple reduction and power loss minimization for each arm individually
Solution Approach 2:
The control method dynamically switches between peak current mode and average current mode based on real-time operating conditions. The controller adjusts the control mode for each arm according to the instantaneous current ripple characteristics, enabling adaptive optimization of the trade-off between voltage ripple and power losses
2Manufacturing precision
If large capacitance is used to reduce capacitor voltage ripple, then voltage ripple is minimized, but the volume and cost of passive components increase
Solution Approach 1:
The patent changes the control parameters and strategies dynamically to achieve better voltage ripple performance without increasing capacitance. By implementing hybrid current mode control with adaptive mode switching, the system achieves reduced voltage ripple through intelligent control rather than through increased passive component size
3Ease of operation
If uniform control mode is applied to all arms, then control simplicity is maintained, but optimization of capacitor voltage ripple is limited
Solution Approach 1:
The patent implements different control modes for different arms based on their specific operating characteristics. Each arm can operate in either peak current mode or average current mode depending on its instantaneous current ripple, allowing optimized voltage ripple reduction for each arm while maintaining overall system manageability through a unified control framework
Data Source
AI summary
Aspects of hybrid-current-mode switching-cycle control are described. In one embodiment, a peak current mode is selected to control a switching power cell. The switching power cell is in an arm of a phase leg of a modular multilevel converter. The phase leg includes an upper arm and a lower arm, and the switching power cell includes a capacitor and at least one switch. At least one switch control signal switches the switching power cell according to a peak current mode based on at least one arm current boundary crossing identified for the arm.