DC Bus Pre-Charge Circuit for Low-Loss AC Inrush Control
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Solution Overview
Problem
Conventional transport refrigeration systems face issues with high surge currents when drawing power from external AC sources, leading to energy dissipation as heat and size/mass penalties due to the use of large passive resistors for current limiting.
Innovation Solution
An electrical apparatus with a pre-charge circuit and control system that pre-charges the DC bus, allowing controlled activation of the AC power module to the external AC power supply, reducing the risk of surge currents through a controllable current source and capacitor-based filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large passive resistor is used to limit the initial current drawn from the external AC power supply, then the risk of current surge is reduced, but energy is dissipated as heat and size/mass penalties occur
Solution Approach 1:
The patent changes the electrical parameters dynamically by using a controllable current source that adjusts its output current based on the charging state of the DC bus. The current source transitions from providing high pre-charging current when the DC bus voltage is low to reducing current as the DC bus voltage approaches its operating level, thereby limiting surge current without dissipating excessive energy as heat in a passive resistor
Solution Approach 2:
The patent replaces the passive mechanical/resistive current limiting approach with an active electronic control system. The controllable current source, governed by a control system that monitors DC bus voltage and regulates current output, substitutes for the simple passive resistor, achieving superior current surge protection with minimal energy loss
2Reliability
If a large passive resistor is used to limit the initial current drawn from the external AC power supply, then the risk of current surge is reduced, but size and mass penalties occur
Solution Approach 1:
The patent uses a controllable current source that dynamically adjusts its electrical parameters based on real-time monitoring of the DC bus voltage. This active control approach replaces the need for large passive resistors, significantly reducing the size and mass of the electrical apparatus while maintaining effective current surge protection
Solution Approach 2:
The patent extracts and removes the unnecessary large passive resistor from the system by implementing an active pre-charge circuit with a controllable current source. This eliminates the mass penalty associated with large resistive components while achieving the same or better current limiting function through electronic control
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 minimizes energy dissipation, increases efficiency, and reduces the size and mass of the electrical apparatus by effectively managing current surges without the need for large passive components.
Implementation Method 1
an AC power module (220) including a rectifier system (222)
Implementation Method 2
the AC power module (220) comprises a filter (224) including a capacitor
Data Source
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AI summary
The present disclosure relates to an electrical apparatus 100 comprising: an AC power module 220 including a rectifier system 222; a DC bus 230 configured to electrically couple the AC power module 220 to a core power module 240 including at least one DC electrical component 242, 244; a pre-charge circuit 260; and a control system 290. The control system 290 is configured to: responsive to a pre-charge initiation signal, perform 310 a pre-charging procedure for pre-charging the DC bus 230, the pre-charging procedure including: activating 314 the pre-charge circuit 260 to provide a pre-charging current to the DC bus 230; monitoring 316 a voltage on the DC bus 230; and responsive to a determination 317 that the monitored voltage on the DC bus has reached a pre-charging threshold, perform 320 a run procedure including: deactivating the pre-charge circuit 260; and electrically coupling the AC power module 220 to an external AC power supply 202 via an AC bus 210.