Changeover Switching Circuit for Low-Energy Backup Power
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Solution Overview
Problem
Existing changeover devices for backup power systems in stable grids are complex, expensive, and require significant energy to maintain, especially in small systems where grid failures are rare, due to the need for switches to be actively kept closed most of the time.
Innovation Solution
A compact changeover device with a switching circuit featuring two normally closed contacts and one normally open contact, which only consumes energy during grid failures, allowing for efficient switching between grid and inverter power sources, reducing energy expenditure and costs by eliminating the need for constant actuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If normally open switches are used for changeover in backup power systems, then safety is improved by ensuring switches are open in idle state, but energy consumption increases significantly because switches must be actively kept closed 98% or more of the time
Solution Approach 1:
The patent inverts the conventional approach by using normally closed switches instead of normally open switches. This inversion allows the switches to remain closed during normal operation without active control, and only opens when grid failure is detected. The changeover device includes switches that are closed in the idle state and open upon detection of grid failure, fundamentally reversing the conventional switching logic to eliminate continuous energy consumption.
Solution Approach 2:
The changeover device automatically detects grid failure and actuates the switches without requiring continuous external control signals. The device monitors the grid state and self-actuates the normally closed switches to open position when failure is detected, eliminating the need for continuous active control and associated energy consumption while maintaining safety through automatic operation.
2Reliability
If switches are designed for full current-carrying capacity of all connected loads, then reliability is improved by ensuring safe operation during short circuits, but device complexity and cost increase significantly
Solution Approach 1:
The patent segments the electrical system into distinct zones: the changeover device with its switches, and the downstream circuit protection devices. By placing the normally closed switches upstream of the loads and relying on downstream circuit breakers or fuses for short circuit protection, the switches themselves do not need to be designed for full short circuit current capacity. This segmentation allows use of simpler, less expensive switches while maintaining overall system reliability through coordinated protection.
Solution Approach 2:
The patent introduces downstream circuit protection devices (circuit breakers or fuses) as intermediaries between the changeover switches and the loads. These intermediary devices handle the short circuit current protection function, allowing the changeover switches to be designed with simpler specifications. The circuit breakers act as mediators that protect the system during fault conditions without requiring the changeover switches to be overly robust.
3Reliability
If changeover devices are installed in small backup power systems with rare grid failures, then safety protection is provided, but cost and energy expenditure become unjustifiably high due to constant switch actuation requirements
Solution Approach 1:
The patent applies the inversion principle to make the changeover device cost-effective for small systems with rare grid failures. By using normally closed switches that remain closed without active control and only open upon grid failure detection, the device eliminates continuous energy consumption and reduces operational costs. This makes the backup protection economically viable even for small systems where grid failures occur infrequently.
Solution Approach 2:
The changeover device automatically monitors grid status and actuates switches only when needed, without requiring continuous external control or energy input. This self-service operation eliminates the need for continuous energy expenditure to maintain switch position, making the system cost-effective for small backup power applications where grid failures are rare events rather than continuous conditions.
Data Source
AI summary
A changeover device for selectively supplying power to at least one load from a grid or a bidirectional inverter includes an input having a grid neutral conductor connection and a grid phase conductor connection for connection to the grid. The changeover device further includes a first output having an inverter neutral conductor connection and an inverter phase conductor connection for connecting the bidirectional inverter, a second output having a load neutral conductor connection and a load phase conductor connection for connecting the load and a switching circuit, the actuator of which is connected to an actuator input of the changeover device. The switching circuit includes a first and a second normally closed contact and a normally open contact that are connected in an interconnection to the grid phase conductor connection, the inverter phase conductor connection, and the load phase conductor connection. An associated method is also disclosed.