DC Load Overload Protection via Ramped Voltage Monitoring
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Solution Overview
Problem
Existing overload protection systems for DC load circuit output modules in safety control systems often shut down prematurely due to conservative monitoring methods, which can lead to unnecessary module shutdowns and failure to handle high surge currents or prolonged turn-on characteristics of loads like capacitors.
Innovation Solution
A method that continuously monitors load current and voltage in real-time during energization, allowing the load current to exceed a threshold as long as the voltage increases at a predetermined rate and does not decrease, thereby enabling longer high-amplitude current durations without causing steady-state damage to output FETs, and includes a ramped load voltage waveform to assess overload conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conservative overload monitoring is used, then circuit protection is ensured, but unnecessary module shutdowns occur and surge current handling capability is reduced
Solution Approach 1:
The monitoring system dynamically adjusts the overload threshold based on the voltage ramp rate. During turn-on, the system accepts higher current thresholds temporarily while the voltage rises, then transitions to normal monitoring. This dynamic adaptation allows the circuit to handle surge currents during capacitive load energization while maintaining protection against actual overloads.
Solution Approach 2:
The system detects the voltage ramp condition in advance and preemptively adjusts the monitoring parameters before the overload condition is fully established. By identifying the voltage ramp rate early in the turn-on sequence, the system prepares the appropriate monitoring threshold, preventing false shutdowns before they occur.
2Measurement precision
If real-time voltage and current monitoring is implemented, then accurate overload detection is achieved, but system complexity increases
Solution Approach 1:
The monitoring system uses a single integrated controller that performs multiple functions: voltage monitoring, current monitoring, ramp rate calculation, threshold adjustment, and overload detection. This multi-functional approach achieves precise overload detection without requiring separate dedicated circuits for each function, thereby limiting the increase in system complexity.
Solution Approach 2:
The system changes the monitoring parameters (current threshold) based on the voltage ramp rate condition. By adjusting the threshold parameter dynamically rather than using a fixed threshold, the system achieves accurate detection across different operating conditions without adding complex hardware, as the parameter adjustment can be implemented through software or control logic.
Data Source
AI summary
This invention relates to overload protection for a circuit driving a direct current (DC) load. The invention provides a method of generating an overload condition for an output module driving a load having a load current and a load voltage comprising the steps of: monitoring the load current at sample intervals; comparing the monitored load current to a predetermined load current threshold; starting an overload timer in the event that the timer is not running and the monitored load current is greater than said load current threshold; monitoring the load voltage at said sample intervals; generating a ramped load voltage waveform for reference purposes in dependence upon an initial load voltage and a predetermined step size load voltage in the event that the overload timer is running; generating an overload condition in the event that the monitored load voltage is less than said ramped load voltage reference waveform, the ramped load voltage is less than a predetermined positive ramp limit and the overload timer is running.