EV Charger Relay Arc Protection via Zero-Crossing Control
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Solution Overview
Problem
AC electric vehicle supply equipment experiences high inrush currents when relays or contactors close, leading to damage, malfunction, and safety concerns due to contact bounce and lack of condition monitoring.
Innovation Solution
The electric vehicle supply equipment incorporates a relay apparatus with a master relay, auxiliary relay, and controllable switch, controlled by a controller to implement zero-voltage and zero-current turning on, using a series branch and parallel configuration to manage the power loop and minimize current flow during switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If relays or contactors are closed to supply power to the electric vehicle, then power transmission is enabled, but high inrush current damages the switch contacts and reduces relay lifetime
Solution Approach 1:
The patent applies preliminary action by first closing the auxiliary relay to charge the capacitor before closing the master relay. This preparatory charging of the capacitor reduces the inrush current that would otherwise flow when the master relay closes, thereby protecting the switch contacts from damage and extending relay lifetime while still enabling power transmission.
2Power
If mechanical relays are used for power switching, then power control is achieved, but contact bounce causes malfunction and reduces reliability
Solution Approach 1:
The patent uses a capacitor as an intermediary element between the power source and the load. The capacitor absorbs the inrush current and smooths out contact bounce effects, allowing the mechanical relay to control power effectively while maintaining contact stability and preventing malfunction.
3Volume of moving object
If relays are miniaturized to reduce device size, then space is saved, but contact protection functions are lost
Solution Approach 1:
The patent segments the relay system into a master relay and an auxiliary relay, where the auxiliary relay specifically handles the protective function. This segmentation allows the main relay to remain compact while the auxiliary relay provides dedicated contact protection through capacitor charging, thus maintaining both small size and reliability.
4Reliability
If zero-voltage and zero-current turning on is implemented, then switch contacts are protected from arcing, but control complexity increases
Solution Approach 1:
The patent implements self-service by using the capacitor to automatically manage the inrush current and enable zero-voltage/zero-current switching. The capacitor charges itself through the auxiliary relay before the master relay closes, and this self-charging mechanism provides arc protection without requiring complex external control circuits, thus maintaining simplicity while achieving contact protection.
Data Source
AI summary
An electric vehicle supply equipment receives an external AC power source. The electric vehicle supply equipment includes a relay apparatus and a controller. The relay apparatus has a master relay, an auxiliary relay, and a controllable switch. The master relay is connected to a master power loop. The controllable switch is connected in series to the auxiliary relay to form a series path and connected to an auxiliary power loop. When the controller detects the external AC power source, the controller turns on the auxiliary relay. Afterward, when the controller detects that the external AC power source is in a zero-crossing condition, the controller drives the controllable switch to be turned on. Accordingly, the relays are controlled in coordinated timing, and further the external AC power source is detected, thus implementing the zero-voltage and zero-current turning on of the relay apparatus.