EV On-Board Charger Pre-Charging via Instantaneous Frequency Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
On-board chargers (OBCs) for electric vehicles face challenges in pre-charging their DC link capacitors without causing inrush electrical currents, which can damage internal components or the mains supply, and are susceptible to domestic network noise.
Innovation Solution
The implementation of a soft-start control strategy that uses a controller to progressively charge the DC link capacitor by triggering power switches during specific cycles of the AC voltage, based on detected instantaneous frequency, to minimize inrush currents and immune the system from noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the DC link capacitor is charged directly without pre-charge control, then the charging speed is fast, but inrush electrical currents are generated that can damage internal components or the mains supply
Solution Approach 1:
The patent applies preliminary action by implementing a pre-charge control strategy that activates before the main charging operation. The controller progressively charges the DC link capacitor through controlled triggering of power switches during specific AC voltage cycles, preparing the system in advance to avoid inrush currents when full power charging begins. This preliminary charging phase ensures the capacitor is ready for normal operation without causing harmful current spikes.
Solution Approach 2:
The patent employs periodic action by triggering the power switches at specific intervals during AC voltage cycles. The controller detects instantaneous frequency during odd half-cycles and triggers switch closure during even half-cycles, creating a periodic charging pattern that progressively builds voltage on the DC link capacitor. This periodic switching strategy controls the charging rate to prevent inrush currents while maintaining efficient charging.
2Measurement precision
If the switch is triggered based on multiple zero-voltage crossings for frequency detection, then the frequency detection is more accurate, but the system becomes susceptible to domestic network noise
Solution Approach 1:
The patent applies the taking out principle by extracting only the essential frequency detection information from a single odd half-cycle of the AC voltage. Instead of analyzing multiple zero-voltage crossings that would expose the system to more noise, the controller measures the instantaneous frequency based solely on the duration of one odd half-cycle. This selective extraction of frequency information from a limited time window maintains measurement accuracy while minimizing noise susceptibility.
Solution Approach 2:
The patent uses preliminary action by completing the frequency detection measurement during the odd half-cycle before the even half-cycle triggering occurs. The controller captures the instantaneous frequency information in advance during the measurement phase, then uses this pre-acquired data to control the switch triggering in the subsequent phase. This preliminary measurement approach ensures accurate frequency detection is available before charging activation, reducing noise exposure.
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 approach effectively prevents damage from inrush currents and reduces noise interference, ensuring safe and efficient pre-charging of the DC link capacitor while maintaining a stable operation.
Implementation Method 1
The frequency sensor is configured to detect during the odd half-cycle of a first cycle of the AC voltage an instantaneous frequency of the AC voltage for the first cycle based on elapsed time between zero-voltage crossings of the odd half-cycle of the first cycle
Implementation Method 2
The capacitor is enabled to be charged with the AC voltage via the switch while the switch is closed
Implementation Method 3
The DC link capacitor is to be progressively charged so that inrush electrical currents are avoided. Inrush electrical currents could damage internal components of the OBC or the mains supply.
Data Source
AI summary
An on-board charger for an electric vehicle includes a switch configured to receive an AC voltage, a capacitor connected to the switch and connectable to a traction battery of the electric vehicle, a frequency sensor, and a controller. The frequency sensor is configured to detect during the odd half-cycle of a first cycle of the AC voltage an instantaneous frequency of the AC voltage for the first cycle based on elapsed time between zero-voltage crossings of the odd half-cycle of the first cycle and not based on any other zero-voltage crossings of the AC voltage. The controller is configured to close the switch during the even half-cycle of the first cycle at a first trigger time dependent upon the instantaneous frequency of the AC voltage for the first cycle. The capacitor is enabled to be charged with the AC voltage via the switch while the switch is closed.