UPS Relay Arc Mitigation via Zero-Crossing Switching
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Solution Overview
Problem
Uninterruptible power supplies (UPS) face challenges in managing voltage swells, which can lead to inverter backfeed and damage electrical components due to unwanted fluctuations in input power, resulting in energy waste, increased costs, and productivity loss.
Innovation Solution
The implementation of a UPS system with a controller that detects voltage swells and controls relays to switch from coupling the input power to the inverter, maintaining a constant DC bus voltage by switching between configurations during a predefined phase angle range relative to the input AC voltage zero crossing, thereby preventing inverter backfeed and maintaining stable power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the relay switches immediately upon detecting voltage swell, then the response time is reduced, but electrical arcs are generated causing inverter backfeed and component damage
Solution Approach 1:
The controller detects voltage swell conditions and initiates relay switching at a predetermined time before the AC voltage zero crossing point. This preliminary action allows the relay to be in the process of switching when the voltage naturally approaches zero, reducing the voltage differential across the relay contacts and minimizing electrical arc generation that causes inverter backfeed and component damage.
Solution Approach 2:
The system changes the timing parameter of relay switching from immediate response to predetermined delay before zero crossing. By adjusting the switching moment to coincide with the natural voltage zero crossing point, the voltage stress on the relay contacts is minimized, preventing harmful electrical arcs while maintaining effective voltage swell protection.
2Reliability
If the relay switching is delayed to avoid electrical arcs, then component damage is prevented, but the response time to voltage swell increases
Solution Approach 1:
The controller performs preliminary detection of voltage swell conditions and schedules the relay switching to occur at the optimal moment - a predetermined time before the AC voltage zero crossing. This approach maintains component protection by avoiding immediate switching that causes arcs, while still achieving rapid response by preparing the switching action as soon as the voltage swell is detected.
Solution Approach 2:
The controller continuously monitors the AC voltage waveform and uses this feedback to determine the precise timing for relay switching. By detecting the voltage swell condition and calculating the upcoming zero crossing point, the system dynamically adjusts the switching timing to achieve both fast response and component protection simultaneously.
3Object-affected harmful factors
If zero-crossing synchronized switching is used, then electrical arcs are minimized, but the switching precision requirement increases
Solution Approach 1:
Instead of requiring precise switching exactly at the zero crossing point, the system uses preliminary action by initiating the relay switching process a predetermined time before the zero crossing. This approach maintains arc suppression benefits while reducing the stringent timing precision requirements, as the relay has sufficient time to complete its switching operation as the voltage naturally approaches zero.
Solution Approach 2:
The predetermined time interval before zero crossing acts as a cushioning period that accommodates the relay's mechanical switching time and reduces timing precision requirements. This cushioning approach ensures that even with variations in relay switching speed, the voltage differential across contacts remains low enough to prevent harmful arcs.
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 effectively prevents inverter backfeed and maintains a stable power output during voltage swells, reducing the risk of component damage and ensuring reliable operation by controlling the switching of relays within a specific time frame relative to the input voltage zero crossing.
Implementation Method 1
a controller that detects voltage swells and controls relays to switch from coupling the input power to the inverter, maintaining a constant DC bus voltage by switching between configurations during a predefined phase angle range relative to the input AC voltage zero crossing
Data Source
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AI summary
Systems and methods of providing power with an uninterruptible power supply are provided. The uninterruptible power supply includes a first input to receive an input AC voltage from a power source, the input AC voltage having an associated phase angle, and a second input to receive an input voltage from a backup power source. The uninterruptible power supply also includes an output. The output provides output power derived from power from at least one of the power source and the backup power source. The uninterruptible power supply also includes an inverter coupled to the backup power source, a relay and a controller. The relay is configured to couple the first input with the output in a first position, and to couple the inverter with the output in a second position. The controller is configured to detect a voltage swell condition of the input voltage, and responsive to detection of the voltage swell condition, control the relay to switch from the first position to the second position during a predefined range of phase angles of the input AC voltage.