Power Converter Switching Frequency Control for Stable Operation
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Solution Overview
Problem
Existing power conversion devices, such as modular multilevel converters, do not adequately stabilize operation by adjusting switching frequency in response to conditions other than ground faults on the AC side, leading to potential instability.
Innovation Solution
A power conversion device with a control system that increases the switching frequency of switching elements based on predefined thresholds or conditions, including control command values, AC circuit parameters, circulating current, capacitor voltage variations, and system states, to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching frequency is increased to stabilize operation, then the stability of the power conversion device is improved, but the loss of energy increases
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable rather than fixed. The control device dynamically changes the switching frequency based on detected operating conditions (ground faults, circulating current, capacitor voltage variations), allowing the system to optimize between stability and energy loss in real-time.
Solution Approach 2:
The patent changes the parameter of switching frequency based on different operating conditions. By detecting conditions such as ground faults, excessive circulating current, or capacitor voltage variations, the control device adjusts the switching frequency parameter to stabilize operation only when necessary, thereby reducing unnecessary energy losses during normal operation.
2Reliability
If the switching frequency is increased to respond to multiple conditions, then the stability of operation is improved, but the device complexity increases
Solution Approach 1:
The control device is designed with multi-functionality to handle multiple different conditions (ground faults, circulating current issues, capacitor voltage variations) using a unified control architecture. This universal approach allows the system to maintain stability across various scenarios without requiring separate complex control systems for each condition.
Solution Approach 2:
The patent implements feedback mechanisms where the control device continuously detects operating conditions and adjusts the switching frequency accordingly. This feedback-based control simplifies the overall system by using a single adaptive control loop that responds to multiple different conditions rather than requiring multiple independent control systems.
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 performs first control to increase a switching frequency of the switching element when a control command value for the self-commutated power converter becomes equal to or greater than a first threshold value.