Solid State Power Controller Inrush Current Limiting
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Solution Overview
Problem
Inrush current surges when high capacitive loads are switched on, causing damage and system faults in power distribution systems, particularly in aircraft applications, and existing solutions with pre-charge resistors increase system volume, weight, and cost.
Innovation Solution
The proposed solution actively controls current supplied to the load using a solid-state power controller (SSPC) by regulating power dissipation based on thermal thresholds, eliminating the need for additional pre-charge circuitry and incorporating a dissipative power regulator and current sensor to manage power dissipation during pre-charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If pre-charge resistors are used to limit inrush current, then inrush current is limited, but system volume, weight, and cost increase
Solution Approach 1:
The patent replaces mechanical pre-charge resistors and electromechanical relays with a solid-state power controller that uses electronic switching and control circuitry to limit inrush current. The SSPC uses pulse-width modulation (PWM) to control the switching of power semiconductor devices, eliminating the need for physical pre-charge resistors and reducing system weight while maintaining inrush current limiting functionality.
Solution Approach 2:
The patent changes the operating parameters of the solid-state switches by controlling their duty cycle and switching frequency through PWM modulation. This allows dynamic adjustment of the effective resistance during pre-charge, enabling inrush current limiting without fixed pre-charge resistors. The duty cycle is varied to control the average current flow during the pre-charge phase.
2Object-affected harmful factors
If pre-charge resistors are used to limit inrush current, then inrush current is limited, but system volume and cost increase
Solution Approach 1:
The patent merges the inrush current limiting function with the main power switching function by integrating pre-charge control into the solid-state power controller. The same PWM control circuitry that controls power delivery to the load also manages the pre-charge phase, eliminating the need for separate pre-charge resistors and control circuits. This consolidation reduces system complexity and component count.
Solution Approach 2:
The solid-state power controller performs multiple functions including inrush current limiting, power switching, and load control through a single integrated device. The PWM controller can operate in different modes (pre-charge mode, full power mode, shutdown mode) depending on the operational requirements, making the system more versatile without adding complexity.
3Object-affected harmful factors
If pre-charge circuitry is added to the load, then inrush current is limited, but reliability decreases
Solution Approach 1:
The patent replaces electromechanical relays and mechanical pre-charge switches with solid-state PWM-controlled switching. Solid-state devices have no moving parts, eliminating contact wear, arcing, and mechanical failure modes. The PWM control provides smooth transitions without the abrupt switching of mechanical contacts, reducing electromagnetic interference and improving reliability.
4Object-affected harmful factors
If active current control is implemented, then inrush current is limited, but control complexity increases
Solution Approach 1:
The patent uses periodic PWM switching to control the current flow during pre-charge. By switching the power semiconductor devices at high frequency with controlled duty cycles, the system achieves effective current limiting through average value control. This periodic switching approach simplifies the control logic compared to continuous analog control while maintaining precise current management.
Solution Approach 2:
The patent implements feedback control by monitoring the current or voltage during pre-charge and adjusting the PWM duty cycle accordingly. The controller compares the actual state with the desired state and modifies the switching signals to maintain proper pre-charge current levels, enabling automatic adaptation without complex manual tuning.
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
This approach effectively limits inrush current, minimizes pre-charge time, and enhances system reliability without the need for additional components, reducing the risk of bus voltage drops and electromagnetic interference.
Implementation Method 1
controlling said current flowing through said load system by said solid state power controller as a function of power dissipation of said solid state switch
Data Source
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Figure 3
AI summary
A solid state power controller, SSPC, having an input to receive supply current and an output for providing output current to a load in response to connection to the power supply, the solid state power controller further comprising at least one solid state switch and a controller to limit the power dissipated in the solid state power switch based on a measured voltage across the solid state switch and a predetermined power dissipation threshold for the SSPC to adjust the output current or voltage control signal of the solid state switch such that the actual power dissipation of the SSPC does not exceed the threshold.