Charger Relay Control Using AC Voltage Frequency and Effective Value
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Solution Overview
Problem
Conventional vehicle chargers experience relay hunting and inefficient charging when the frequency of AC voltage is low, leading to premature halting and resumption of external charging, which can deteriorate the relay due to fluctuations in instantaneous AC voltage values.
Innovation Solution
A charger with a controller that calculates the effective value and frequency of AC voltage over a predetermined period, maintaining the relay in an open state if the effective value is below a threshold and in a closed state if the frequency is above a threshold, preventing hunting by ensuring continuous charging even at low frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the charger halts external charging when the calculated effective value of AC voltage is less than a voltage threshold, then the relay is protected from damage due to low voltage conditions, but relay hunting occurs at very low frequencies causing periodic opening and closing that deteriorates the relay
Solution Approach 1:
The patent changes the control parameters from voltage-only monitoring to dual parameter monitoring (voltage and frequency). The controller now considers both the effective value of AC voltage and the frequency of AC voltage when determining relay operation, preventing relay hunting by requiring frequency to be above a threshold before allowing relay closing, while maintaining voltage threshold protection
Solution Approach 2:
The patent implements dynamic control of the relay based on real-time monitoring of both voltage and frequency parameters. The relay operation state is dynamically adjusted according to the combined conditions of voltage effective value and frequency, allowing the system to adapt to varying AC power supply conditions and prevent premature relay operation at very low frequencies
2Productivity
If the relay is controlled to close during external charging to enable continuous power flow, then charging efficiency is improved, but the relay experiences hunting and periodic opening/closing at very low frequencies leading to deterioration
Solution Approach 1:
The patent introduces frequency as an additional control parameter alongside voltage. The relay closing condition now requires both voltage effective value and frequency to be above their respective thresholds, preventing the relay from closing at very low frequencies where hunting would occur, thus protecting relay lifespan while maintaining charging efficiency under normal conditions
Solution Approach 2:
The patent implements feedback control by continuously monitoring both voltage and frequency parameters and using this information to control relay operation. The controller adjusts relay state based on real-time feedback from voltage and frequency measurements, preventing hunting by maintaining relay in the off state when frequency is below threshold, even if voltage appears adequate
Data Source
AI summary
A charger includes: a relay provided between an input line and a conversion circuit; a voltage sensor that detects AC voltage input to the input line; and a controller that calculates effective value and frequency of the AC voltage based on a waveform of the AC voltage for a predetermined period. When the calculated effective value of the AC voltage is smaller than a voltage threshold during execution of external charging, the controller brings the relay into an open state. When the calculated effective value of the AC voltage is larger than the voltage threshold and the calculated frequency of the AC voltage is larger than a frequency threshold value after the external charging is halted, the controller brings the relay into a close state.