Power Converter Current Limit Control via Predictive Signal Level
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Solution Overview
Problem
Existing peak current control devices for power converters are unstable at duty cycles greater than fifty percent, exhibit sub-harmonic oscillations, and are sensitive to switching noise, making them unsuitable for precise average load current control independent of duty cycle variations.
Innovation Solution
A current limit control apparatus and method that includes a signal sensor, signal level predictor, comparer, and control unit to sense and predict signal levels during switching cycles, preventing modulating signals to the power converter when excessive current is detected, thus stabilizing current control and reducing noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If peak current control is used for fast response to over-current conditions, then response speed is improved, but stability deteriorates when duty cycle exceeds fifty percent causing sub-harmonic oscillation
Solution Approach 1:
The patent applies preliminary action by predicting the peak current level for the current switching cycle based on the duty cycle from the previous switching cycle. This predictive approach allows the system to prepare the current limit threshold in advance, avoiding the stability issues that arise when using real-time peak current sensing during the switching cycle itself. The predicted peak current is calculated before the switching cycle begins, ensuring stable control even when duty cycle exceeds fifty percent.
2Measurement precision
If peak current control device is designed to be sensitive to current changes, then current detection precision is improved, but noise sensitivity increases causing false alarms
Solution Approach 1:
The patent eliminates noise sensitivity issues by performing current limit control predictions before the switching cycle begins. The predicted peak current is calculated using the duty cycle from the previous cycle and stored in a register, so no real-time sensing during switching is required. This preliminary calculation approach achieves precise current control without being affected by switching noise or spurious injections that would cause false alarms in traditional peak current control devices.
Solution Approach 2:
The patent introduces an intermediary approach by using the duty cycle signal as a mediator to predict the peak current. Instead of directly sensing the peak current during switching (which is noisy), the system uses the clean duty cycle signal from the previous cycle to calculate and predict the current limit threshold. This intermediary method transfers the control function to a noise-free domain while maintaining precise current control.
3Reliability
If peak current control is used to protect against excessive current, then current protection is improved, but average load current control precision deteriorates due to large variations with duty cycle
Solution Approach 1:
The patent applies parameter changes by shifting the control parameter from direct peak current sensing to predicted peak current based on duty cycle. By changing the control parameter to a predicted value calculated from the duty cycle of the previous switching cycle, the system maintains reliable current protection while achieving precise average load current control that is substantially independent of duty cycle variations. This parameter transformation eliminates the large variations inherent in traditional peak current control.
Data Source
AI summary
An apparatus for controlling a power converter operating in response to a modulating signal during successive switching cycles includes: (a) A signal sensor coupled with the converter and sensing an extant signal during the extant cycle. (b) A signal level predictor coupled for receiving a reference signal and establishing a predicted level for the extant switching cycle. (c) A comparer coupled with the signal sensor and the signal level predictor for presenting a first output signal when the extant signal and the predicted signal level have a first relationship and for presenting a second output signal when the extant signal and the predicted signal level have a second relationship. (d) A control unit coupled with the comparer and with the converter for interrupting presentation of the modulating signal to the converter device when the comparing unit presents a selected one of the first and second output signals.