Marine Drive Pre-Charge Circuit for Link Capacitor Inrush Control
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Solution Overview
Problem
Existing electric marine propulsion systems face issues with high inrush currents when connecting batteries to link capacitors, leading to potential arcing, welding of contacts, and undesirable heat emissions, which can damage components and reduce energy efficiency.
Innovation Solution
A current limiting circuit with an inductor and MOSFET switches controls current flow to pre-charge and discharge the link capacitor, limiting initial current to safe levels and enabling energy recovery, using a parallel path with a high current switch to maintain consistent voltage and prevent high inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If direct connection is made between power storage system and link capacitor, then charging speed is improved, but inrush current increases causing arcing and welding of contacts
Solution Approach 1:
A pre-charge resistor is connected in parallel with the main power switch to provide a controlled charging path for the link capacitor before the main switch closes. This preliminary action charges the capacitor through a current-limiting resistor, preventing inrush current when the main connection is made, while still allowing fast charging afterward when the pre-charge path is bypassed.
2Power
If high current switch is used to allow sufficient current flow, then power delivery is improved, but heat emissions increase
Solution Approach 1:
The current path is segmented into two parallel paths: a pre-charge path through a current-limiting resistor and a main power path through a low-resistance switch. During pre-charge, current flows through the resistor at limited levels. When the main switch closes, the majority of current flows through the low-resistance main path, providing high power delivery with minimal heat generation in the switching component.
3Reliability
If current limiting circuit is added to control inrush current, then component safety is improved, but device complexity increases
Solution Approach 1:
The pre-charge resistor is merged with the main power switch into a single parallel configuration. The same two components serve dual purposes: the resistor limits inrush current during pre-charge, and the switch provides low-resistance path for main power flow. This integration achieves component protection without adding separate complex protection circuits.
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
The solution effectively prevents damage to components, conserves energy, reduces heat emissions, and enhances system efficiency by managing current flow during capacitor charging and discharging, ensuring safe and reliable operation.
Implementation Method 1
the current limiting circuit comprises an inductor between the power storage system and the link capacitor
Implementation Method 2
two MOSFET switches configured to provide alternate current paths to the inductor
Implementation Method 3
a link capacitor connected to the electric motor in parallel with the power storage system
Data Source
AI summary
A marine propulsion system includes an electric marine drive comprising an electric motor powered by a power storage system, a link capacitor connected to the electric motor in parallel with the power storage system, and a high current switch positioned in a main current path between the power storage system and the electric motor and configured to have an on state that allows sufficient current to flow from the power storage system to power the electric motor and an off state that blocks bidirectional current flow along the main current path. A current limiting circuit is positioned in parallel with the high current switch and is configured to provide a controlled current to charge the link capacitor while the high current switch remains in the off state and may also be configured to control current flow from the link capacitor to the power storage system to recover power from the link capacitor while the high current switch remains in the off state.