Converter Startup Control for DC Link Overcurrent Prevention
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Solution Overview
Problem
Conventional DC power transmission equipment faces issues with overcurrent flow when starting current-type and voltage-type converters, potentially leading to malfunction and damage to semiconductor elements.
Innovation Solution
A power conversion device with a voltage-type first power converter and a current-type second power converter, connected via a DC circuit, includes a control unit that adjusts the DC voltage to a set value to prevent excessive current flow during startup, ensuring the current remains within rated limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If both current-type converter and voltage-type converter are started simultaneously, then power transmission can begin, but excessive current flows through the DC transmission line causing element malfunction
Solution Approach 1:
The control device implements a two-stage startup process where the voltage-type converter is started first and stabilized, then the current-type converter is started subsequently. This preliminary action sequence prevents simultaneous inrush current from both converters, eliminating the overcurrent problem while maintaining reliable element operation.
2Ease of operation
If DC voltage is not controlled during startup, then converter operation is simplified, but excessive current flows beyond rated values
Solution Approach 1:
The control device monitors the DC transmission line current and uses this feedback to dynamically adjust the DC voltage output. When current approaches rated values, the control device reduces voltage to maintain current within safe limits, preventing overcurrent while maintaining controlled operation during startup.
3Power
If DC voltage is increased to improve power transmission efficiency, then power transmission capability increases, but current exceeds rated values during startup
Solution Approach 1:
The control device dynamically adjusts DC voltage based on real-time current conditions rather than maintaining a fixed high voltage. During startup when current is sensitive, voltage is controlled to stay within rated current limits. Once the system stabilizes and current decreases, voltage can be increased to improve power transmission efficiency, achieving both safety and efficiency at different operational stages.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents overcurrent at startup, protecting the semiconductor elements and ensuring reliable operation of the power conversion device by controlling current flow through the DC circuit.
Implementation Method 1
voltage-type first power converter and a current-type second power converter which have semiconductor elements for controlling conduction and interruption of current and perform power conversion between AC and DC
Data Source
AI summary
A power conversion device includes a voltage-type power converter and a current-type power converter each of which performs power conversion between AC and DC, and a controlling circuitry, and power is transmitted/received between AC sides via a DC circuit. In first starting control for starting the voltage-type power converter and the current-type power converter, the controlling circuitry controls a semiconductor element of at least one of the voltage-type power converter and the current-type power converter, to adjust DC voltage at DC terminals of the voltage-type converter to a set first voltage value, thereby controlling current flowing through the DC circuit to be first current not greater than a rated current value of the semiconductor elements.