Hybrid Bridge Transfer Switch for Transformer Inrush Control
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Solution Overview
Problem
Conventional transfer switches face challenges in managing high inrush currents during transformer energization, leading to potential tripping of protection circuit breakers and stress on upstream uninterruptible power supply (UPS) systems, which can result in malfunctions and reduced reliability.
Innovation Solution
A hybrid transfer switch system utilizing different types of solid-state switching devices (SSSDs) for each leg, controlled by a single controller, to manage power transitions and reduce inrush currents, preventing transformer failure and load drop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transfer switch is used to control power supply to critical electrical components, then power source switching capability is improved, but inrush current during transformer energization increases
Solution Approach 1:
The controller pre-charges the transformer core before full energization by initially connecting through the second switch with lower inrush characteristics, then transitioning to the first switch. This preliminary action reduces the flux buildup that causes inrush current while maintaining the power source switching capability.
Solution Approach 2:
The patent introduces a hybrid bridge topology with two different solid state switching device types acting as intermediaries during the power source transition. The first and second switches with different SSSD types work together to mediate the energization process, allowing controlled flux reversal and reduced inrush current while maintaining full power switching capability.
2Duration of action of moving object
If high inrush current is drawn during transformer energization, then transformer reconnection is achieved, but protection circuit breakers trip open
Solution Approach 1:
The controller performs preliminary flux management by controlling the switching sequence of the hybrid SSSD pairs. Before full power connection, the controller prepares the transformer core state through controlled energization, preventing the conditions that lead to breaker tripping while achieving reliable reconnection.
Solution Approach 2:
The patent changes the electrical parameters during energization by using two different types of solid state switching devices with different characteristics. This parameter variation allows the system to energize the transformer under controlled conditions that prevent excessive inrush current and subsequent breaker tripping.
3Reliability
If inrush current during transformer energization is reduced, then system reliability is improved, but switching device complexity increases
Solution Approach 1:
The patent employs a hybrid bridge topology combining two different types of solid state switching devices in the same circuit. This composite approach leverages the complementary characteristics of different SSSD types to reduce inrush current while managing the complexity through a unified controller that coordinates both device types.
Solution Approach 2:
The controller is designed to universally control both types of solid state switching devices, performing multiple functions including flux management, inrush current limitation, and power source switching. This multi-functionality reduces the need for separate control circuits, managing overall system complexity despite the hybrid switching architecture.
Data Source
AI summary
A transfer switch for hybrid switching between a first power source and a second power source, the transfer switch includes a first switch and a second switch, the first and second switch connecting a load to a first power source and a second power source, respectively. The first switch includes at least one first solid state switching device (SSSD) pair. The second switch includes at least one second SSSD pair. The at least one first SSSD pair includes a different type of switching devices relative to the type of switching devices of the at least one second SSSD pair. Moreover, a controller may be configured to selectively cycle the at least one first SSSD pair and the at least one second SSSD pair on and off to electrically couple one of the first power source and the second power source to the load.