Self-Commutated Converter Control for Deviation-Triggered Switching
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Solution Overview
Problem
Existing power conversion devices, such as modular multilevel converters, face instability in operation due to inadequate adjustment of switching frequency beyond ground fault scenarios, leading to inefficiencies and potential system instability.
Innovation Solution
A power conversion device with a self-commutated power converter and a control device that calculates deviations between control commands and feedback values, increasing the switching frequency when deviations exceed a threshold or when the rate of change of control commands surpasses a reference rate, thereby stabilizing operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching frequency is increased to stabilize operation during ground faults, then the reliability improves, but the device complexity and energy loss increase
Solution Approach 1:
The patent dynamically changes the switching frequency parameter based on detected fault conditions. When a ground fault is detected on the AC side, the switching frequency is increased from a first frequency to a second frequency (higher than the first). This parameter change allows the system to maintain stability during faults while avoiding unnecessary complexity during normal operation.
Solution Approach 2:
The patent implements dynamic switching frequency adjustment rather than fixed frequency operation. The control device monitors AC side conditions and adaptively changes the switching frequency in response to ground faults. This dynamic approach improves reliability during faults while keeping the control system relatively simple by only activating high-frequency mode when needed.
2Reliability
If the switching frequency is increased to improve response to control deviations, then the stability improves, but the energy loss increases
Solution Approach 1:
The patent changes the switching frequency parameter dynamically based on control deviations. When the absolute value of deviation between control command and feedback exceeds a threshold, the switching frequency is increased to improve response and stability. When deviation is within acceptable limits, the system operates at lower frequency to minimize energy loss.
Solution Approach 2:
The system dynamically adjusts switching frequency based on real-time control deviation measurements. This allows the system to achieve high stability when needed (large deviations) while minimizing energy loss during normal operation (small deviations), resolving the contradiction between stability and energy efficiency.
3Speed
If the switching frequency is increased to handle rapid changes in control commands, then the responsiveness improves, but the device complexity increases
Solution Approach 1:
The patent changes the switching frequency parameter in response to the rate of change of control commands. When the rate of change exceeds a reference rate, the switching frequency is increased to handle the rapid changes effectively. This parameter adjustment improves responsiveness without permanently increasing system complexity.
Solution Approach 2:
The system dynamically adjusts switching frequency based on the rate of change of control commands. This allows high-speed response when commands change rapidly while maintaining simpler operation during steady-state conditions, resolving the contradiction between responsiveness and complexity.
Data Source
AI summary
A power conversion device includes a self-commutated power converter that performs power conversion between an AC circuit and a DC circuit, and a control device that controls switching operation of a switching element included in the self-commutated power converter. The control device calculates a deviation between a control command value for the self-commutated power converter and a feedback value from the self-commutated power converter, and performs first control to increase a switching frequency of the switching element when the deviation becomes equal to or greater than a first threshold value.