Transformer-less Rectifier UPS Inrush Current Reduction
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Solution Overview
Problem
Transformer-less rectifier UPS systems experience large inrush currents when the circuit breaker is closed, requiring additional design considerations and costs for circuit and fuse design to address these currents.
Innovation Solution
A method that involves pre-charging the DC bus to a voltage equal to the peak AC voltage level and operating the rectifier as an inverter to regulate the AC output voltage, ensuring the circuit breaker is closed only when the AC voltages are equal, thereby minimizing the inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the circuit breaker is closed in a transformer-less rectifier UPS system, then power is supplied to the system, but large inrush currents flow from the AC power source to the capacitors of the LC input circuits
Solution Approach 1:
The patent applies preliminary action by pre-charging the DC bus to a voltage level equal to the peak AC input voltage before closing the circuit breaker. This is achieved by operating the rectifier as an inverter to generate an AC output voltage that matches the AC input voltage, then closing the breaker when voltages are equal, preventing inrush currents from flowing to the LC input circuit capacitors.
2Reliability
If additional design considerations are made for inrush currents, then circuit and fuse design can address the effects of large inrush currents, but design costs and complexity increase
Solution Approach 1:
The patent converts the potentially harmful inrush current phenomenon into a beneficial control mechanism. By using the rectifier-inverter operation to pre-charge the DC bus and synchronize voltages before breaker closure, the method eliminates the need for additional protective devices and complex fuse designs, thereby reducing overall system complexity while maintaining reliability.
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 approach reduces inrush currents, simplifies the design of fuses and circuits, avoids overdesign and resizing costs, and prolongs the life of components by eliminating stress on the input side of the rectifier.
Implementation Method 1
a rectifier that converts AC input power to DC power that is provided via a DC bus
Implementation Method 2
an inverter that converts the DC power back to AC power
Data Source
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AI summary
A method reduces inrush currents in a transformer-less rectifier UPS system when an input circuit breaker (102) of the UPS system is closed from an open position. The circuit breaker is coupled between an AC power input (130) and an AC input of a rectifier (104) of the UPS system and a DC output (108) of the rectifier is coupled to a DC bus (110) of the UPS system. Before the circuit breaker is closed, the DC bus is charged to a DC voltage having a level that is equal to a peak AC voltage level of a line-line AC voltage of AC input power to the UPS system. The rectifier is operated as an inverter to provide an AC output voltage at the AC input of the rectifier that is equal to an AC voltage at the AC power input and when it is equal, the circuit breaker is closed.