Switched Current Sensor Rectification for PWM AC Measurement
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Solution Overview
Problem
Conventional current sensors in DC-DC converters with pulse width modulation experience measurement errors due to alternating currents through diode capacitances during the switch-off phase, leading to inaccurate current measurement and regulation.
Innovation Solution
A current sensor with a coupler, switchable rectifier, and switching signal generator that decouples and rectifies a proportional part of the alternating current only during the switch-on phase of the half-bridge, deactivating rectification during the switch-off phase to prevent measurement of residual currents, using active switching elements like MOSFETs to simplify implementation and avoid complex high-side control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional rectifier is used to measure current in a DC-DC converter, then the current measurement is simple to implement, but measurement errors occur during the switch-off phase due to resonance currents through diode capacitances
Solution Approach 1:
The patent applies dynamics by making the rectifier switchable rather than continuously operating. The rectifier is dynamically controlled to be activated only during the switch-on phase and deactivated during the switch-off phase, allowing it to adapt its behavior based on the converter's operating state. This dynamic control eliminates measurement errors from resonance currents while maintaining implementation simplicity.
Solution Approach 2:
The patent implements periodic action by synchronizing the rectifier's operation with the PWM switching cycle of the converter. The rectifier is periodically activated during switch-on phases and deactivated during switch-off phases, creating a rhythmic on-off pattern that matches the converter's operating cycle. This periodic control ensures accurate current measurement while avoiding errors from resonance currents.
2Measurement precision
If the rectifier is continuously active to measure current, then measurement coverage is complete, but fault currents during switch-off phase contaminate the measurement
Solution Approach 1:
The rectifier operates periodically rather than continuously, being activated only during switch-on phases and deactivated during switch-off phases. This periodic operation pattern ensures that the rectifier measures current only when valid current flows through the converter, excluding the problematic switch-off phase from measurement, thereby improving accuracy while reducing operation duration.
Solution Approach 2:
The rectifier is activated in advance of the current measurement window, specifically turned on just before the switch-on phase begins and turned off just after it ends. This preliminary action timing ensures that the rectifier is ready to measure current immediately when valid current appears, while preventing it from measuring fault currents during the switch-off phase.
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 ensures precise current measurement and regulation by eliminating measurement errors caused by fault currents during the switch-off phase, allowing for accurate control of LED modules and reducing diode capacitance distortion.
Implementation Method 1
a coupler (20) which is designed to couple out a proportional part of the alternating current as a measuring current
Implementation Method 2
a switchable rectifier (21), which is designed to rectify the measuring current controlled by the switching signal and to output it as a rectified measuring current
Data Source
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AI summary
The invention relates to a current sensor (12), which is used to sense an alternating current (16). The current sensor (12) has a coupler (20), which is designed to couple out a proportional part of the alternating current (16) as a measurement current (22). The current sensor (12) also has a switching terminal, which is designed for the feeding in of a switching signal (15). The current sensor (12) additionally contains a switchable rectifier (21), which is designed to rectify the measurement current (22) under the control of the switching signal (15) and to output the measurement current as a rectified measurement current (Vsense).