DC Contactor Sequencing for Bidirectional High-Current Switching
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Solution Overview
Problem
The increasing demand for bidirectional EV chargers requires cost-effective DC contactors capable of safe high current switching in both directions, as many unidirectional DC contactors are not designed to handle reverse current flows without damage, and available bidirectional contactors are expensive with limited rated current options.
Innovation Solution
A DC contactor arrangement using at least one unidirectional contactor, configured to switch at different times based on load conditions, allowing for safe high current switching in both directions by sequencing the operation of DC+ and DC− contactors to prevent damage during reverse power flows, and incorporating a control circuit for signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If bidirectional DC contactors are used to enable high current switching in both directions, then the capability for bidirectional power switching is improved, but the cost increases significantly
Solution Approach 1:
The patent divides the bidirectional contactor system into two separate unidirectional contactors (DC+ contactor for positive current direction and DC− contactor for negative current direction). Each unidirectional contactor is optimized for its specific direction, allowing the use of simpler, less expensive components while collectively achieving bidirectional functionality through coordinated operation controlled by a control unit.
2Ease of manufacture
If unidirectional DC contactors are used to reduce cost, then the cost decreases, but the ability to switch under reverse current flow is lost
Solution Approach 1:
The patent implements multi-functionality by using two unidirectional contactors that collectively perform both forward and reverse switching functions. The control unit coordinates the operation of both contactors to achieve bidirectional power flow control, making the system universally capable of handling both charging and discharging operations with standard unidirectional components.
Solution Approach 2:
The control unit preemptively manages the switching sequence by first opening the appropriate unidirectional contactor before current reversal occurs, preventing reverse current damage. This preliminary action ensures that each unidirectional contactor only operates within its safe current direction while maintaining overall bidirectional system functionality.
3Ease of manufacture
If unidirectional contactors are used, then cost is reduced, but the selection range for rated currents is limited
Solution Approach 1:
The patent overcomes the limited rated current selection by using the control unit to dynamically manage the operation parameters of two unidirectional contactors. By coordinating their switching based on current magnitude and direction, the system can accommodate a broader range of current ratings than a single bidirectional contactor would provide, as each unidirectional contactor can be selected for optimal performance in its specific direction.
4Speed
If DC contactors are switched simultaneously under load, then switching speed is improved, but damage to unidirectional contactors occurs during reverse current flow
Solution Approach 1:
The control unit performs preliminary action by detecting current direction and preemptively opening the appropriate unidirectional contactor before reverse current flow begins. This prevents damage to unidirectional contactors while maintaining fast switching response, as the control unit coordinates the timing of both contactors to ensure safe operation throughout the transition.
Data Source
AI summary
A DC contactor arrangement for bidirectional power switching includes a DC+ contactor for connecting a power source with a load, and a DC− contactor for connecting the power source with the load. At least one of the DC+ or DC− contactors is a unidirectional DC contactor. The DC+ contactor and the DC− contactor are configured to be switched at different times, when the DC+ contactor and the DC− contactor are under load.