Voltage Controlled Solid State Relay for Inrush Current Limiting
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Solution Overview
Problem
Inrush currents during the power-up phase of electric power systems can cause significant stress on input bridge rectifiers and DC capacitors, leading to potential damage and inefficiencies.
Innovation Solution
A solid-state relay (SSR) with a voltage-controlled active semiconductor device, including a switching device and a voltage-controlled circuit with adjustable resistance, is used to regulate and limit the inrush current by operating in a linear mode and adjusting resistance based on voltage feedback, thereby controlling the current flow through the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC capacitor is charged completely from zero charge during power-up, then the capacitor reaches steady state voltage level, but a very high inrush current occurs causing stress on the input bridge rectifier and DC capacitor
Solution Approach 1:
The patent applies dynamics by making the resistance value changeable during the charging process. The resistance is high initially to limit inrush current, then dynamically reduced as the capacitor charges to maintain optimal charging current throughout the charging phases, resolving the contradiction between limiting stress and maintaining charging efficiency
Solution Approach 2:
The patent changes the resistance parameter during the charging process. By adjusting the resistance value from high to low as the capacitor voltage increases, the system limits inrush current while maintaining efficient charging, directly addressing the technical contradiction between component protection and charging speed
2Reliability
If a fixed resistance is used to limit inrush current, then component stress is reduced, but charging efficiency decreases due to excessive resistance during steady state
Solution Approach 1:
The patent uses a dynamically adjustable resistance instead of a fixed resistance. The resistance is high during power-up to protect components, then automatically reduced when the capacitor reaches steady state, eliminating energy waste while maintaining component protection during critical phases
Solution Approach 2:
The patent implements periodic action by dividing the charging process into distinct phases (power-up phase with high resistance, steady state phase with low resistance). This phased approach ensures component protection during initial charging while maximizing efficiency 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
This solution effectively limits inrush currents, reducing stress on components and ensuring stable operation during power-up, while also maintaining efficient charging of the DC capacitor.
Implementation Method 1
a voltage controlled circuit coupled to the switching device along a path of the channel current and having a total effective resistance, where the voltage controlled circuit is configured to regulate the channel current based on the total effective resistance, and where the voltage controlled circuit is configured to change the total effective resistance based on a voltage feedback parameter
Data Source
AI summary
An electric power system includes an input bridge rectifier configured to convert an AC voltage to a DC voltage; a DC capacitor configured to charge to an DC output voltage based on the DC voltage; and a voltage controlled active semiconductor device coupled to the input bridge rectifier to control a current through at least one of the input bridge rectifier and the DC capacitor. The voltage controlled active semiconductor device includes a switching device including a control terminal that receives a control voltage such that the switching device conducts the current based on the control voltage; and a voltage controlled circuit coupled to the switching device along a path of the current and having a total effective resistance. The voltage controlled circuit is configured to regulate the current based on the total effective resistance, and change the total effective resistance based on a voltage feedback parameter.