Parallel Mechanical Relays with Semiconductor Shunts for High Current Switching
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Solution Overview
Problem
The use of multiple mechanical relays in parallel to increase current switching capability is hindered by premature failure due to time differences in contact opening and closing, leading to overcurrent and arcing, which is not effectively addressed by existing technologies.
Innovation Solution
Incorporating a semiconductor switch assembly across the relays to commutate current during transient switching periods, ensuring that the bulk of the load current passes through the semiconductor devices rather than the relay contacts, thereby avoiding overcurrent and arcing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple smaller relays are used in parallel to reduce cost and size, then the overall current capacity is reduced, but the relay contacts are damaged by overcurrent during transient switching periods
Solution Approach 1:
A semiconductor switch assembly is introduced as an intermediary device to commutate current during transient switching periods. The semiconductor switch assembly includes a first switch connected in parallel with the relay contacts and a second switch connected in series with the relay coils, acting as a mediator to redirect current away from the relay contacts during critical transient periods when contacts are opening or closing.
Solution Approach 2:
The semiconductor switch assembly is activated in advance of relay contact closure to establish a current path before the relay contacts close. This preliminary action ensures that when relay contacts close, the current is already flowing through the semiconductor path, preventing inrush current damage to the contacts.
2Speed
If relay contacts are closed quickly to improve switching speed, then the switching time is reduced, but arcing and contact degradation occur due to simultaneous closing of multiple relays
Solution Approach 1:
The semiconductor switch assembly serves as an intermediary that absorbs and commutates the arcing current during relay contact closure. By providing an alternative current path through the semiconductor switches, the harmful arcing between relay contacts is eliminated while maintaining fast switching speeds.
Solution Approach 2:
The patent replaces the purely mechanical relay switching system with a hybrid system that incorporates semiconductor switches. The semiconductor switches handle the high-speed switching and current commutation functions, while the mechanical relay contacts only need to maintain the circuit connection, eliminating arcing and contact degradation associated with mechanical switching.
3Quantity of substance
If a single large relay is used to achieve high current capacity, then the current switching capability is sufficient, but the cost, size and weight increase significantly
Solution Approach 1:
The patent divides a single high-current relay function into multiple smaller relay units connected in parallel. Each smaller relay handles a portion of the total current, and their combined capacity equals or exceeds that of a single large relay. This segmentation reduces the weight, size, and cost of individual relay components while maintaining the required current switching capability.
Solution Approach 2:
The patent combines multiple smaller relay units with a semiconductor switch assembly to create a hybrid system that achieves the current handling capability of a single large relay. The parallel connection of multiple relays merges their current capacities, while the semiconductor switches merge their control functions to coordinate the operation of multiple relays.
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 enables the use of multiple smaller relays in parallel to handle high currents without premature failure, eliminating arcing and contact degradation, and reducing heat dissipation, thus extending relay life and reducing costs and size requirements.
Implementation Method 1
the bulk of the load current passes through the semiconductor switch assembly and not through the relay contacts by virtue of a low on-resistance of the semiconductor switch assembly
Implementation Method 2
a closure of the semiconductor switch assembly occurs before a closure of the relay contacts, wherein, as the relay contacts start to close, the bulk of the load current momentarily passes through the semiconductor switch assembly and not through the relay contacts by virtue of a low on-resistance of the semiconductor switch assembly
Data Source
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AI summary
Multiple relays are connected in parallel by including one or more semiconductor devices connected across the relay contacts. The semiconductor devices are triggered to conduct and shunt transient currents during the opening and closing of the relay contacts to protect the relay contacts from overcurrent and to eliminate arcing during relay switching. This permits a combination of smaller relays to replace a larger and more expensive relay in applications that require switching of large load currents.