DC Switch Load Detection for Safe Inductive Shutdown
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Solution Overview
Problem
Direct current switches face challenges in safely switching off loads with capacitive or inductive characteristics, particularly due to unknown supply inductance and load conditions, leading to potential destruction during shutdown processes.
Innovation Solution
A direct current switch with a power-holding conductor switch, voltage and current measurement devices, and a control device that determines supply inductance and capacity to ensure safe switching off by measuring and controlling the inductance and capacity within permissible limits, using a specific sequence and formula to calculate inductance and capacity values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the semiconductor switch is used to interrupt DC fault current, then the switching speed is improved, but the switch may be destroyed by excessive current rise rates with capacitive loads
Solution Approach 1:
The control device performs preliminary detection of load characteristics (capacitive or inductive) before the actual fault interruption. Based on this preliminary detection, the control device prepares appropriate switching strategies in advance, such as adjusting dead times or activating protection circuits, to prevent destruction while maintaining fast switching capability.
Solution Approach 2:
The control device dynamically changes switching parameters based on detected load characteristics. For capacitive loads with low inductance, the control device increases the turn-off dead time to limit current rise rate. For inductive loads, different timing parameters are applied. This parameter adaptation allows the switch to operate safely across different load types while maintaining high switching speed.
2Speed
If the supply line inductance is very large, then the current rise rate is reduced, but the energy stored in the inductance requires surge protection networks that limit load capacity
Solution Approach 1:
The control device uses the existing supply line inductance to its advantage. By detecting the actual inductance value and load characteristics, the control device automatically adjusts switching parameters to achieve safe operation. The system serves itself by utilizing the natural current limiting effect of the supply line inductance, eliminating the need for additional surge protection networks that would restrict load capacity.
Solution Approach 2:
The control device adapts switching parameters based on the actual supply line inductance detected during commissioning or operation. For high inductance lines, the control device uses shorter dead times and different switching sequences, while for low inductance lines, longer dead times are applied. This parameter adaptation enables the switch to handle various load capacities without requiring fixed surge protection networks.
3Ease of manufacture
If the supply line inductance is unknown, then the switch can be designed for standard conditions, but complex on-site measurements or trial-and-error tests are required to determine actual load conditions
Solution Approach 1:
The control device automatically detects and determines the supply line inductance and load characteristics during a commissioning phase or initial operation. By performing self-diagnosis and parameter identification, the system eliminates the need for complex manual measurements or trial-and-error testing. The switch configures itself for the actual installation conditions, maintaining design simplicity while enabling accurate adaptation to real-world variations.
4Reliability
If the semiconductor switch carries full load current continuously, then the switching capability is maintained, but the switch is permanently on during normal operation increasing power loss
Solution Approach 1:
The control device implements periodic monitoring of load conditions and fault detection. Instead of maintaining the switch in a permanently on state, the system uses periodic sensing to detect faults and activates switching only when necessary. This periodic action maintains switching capability while minimizing the time the switch conducts full load current, thereby reducing power losses during normal operation.
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 allows for safe and controlled shutdown of direct current lines by determining and managing inductance and capacity, preventing destruction and ensuring operational safety without the need for elaborate manual measurements.
Implementation Method 1
control device (25) to switch on the DC switch (20) for a first period of time, to determine the supply-side input voltage, to determine the load-side output voltage present at the end of the first period of time, to determine the current present at the end of the first period of time, and to determine an applied inductance and/or capacitance from the determined values
Data Source
Figure 1~2
Figure 3
AI summary
The DC switch for the controllable disconnection of a DC line is designed to determine the inductance present on the load side by switching it on for a definable period of time, which is significantly shorter than 1 s, and calculating the inductance from at least the current achieved, the input voltage applied, and the length of the period of time.