Three-Phase Charging Device With Single-Resistor Inrush Limiting
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Solution Overview
Problem
Existing charging devices for three-phase power supplies face challenges in suppressing inrush currents while minimizing cost and weight, as providing pre-charge resistors for each relay can lead to increased costs and weight, and unequal voltage swings between phases can cause inrush currents even with pre-charging.
Innovation Solution
A charging device with a first converter, a second converter, relays, and a pre-charge resistor, controlled by a controller to open and close relays sequentially, pre-charging the capacitor via a single pre-charge resistor and boosting the voltage to a target value, suppressing inrush currents by ensuring all relays are closed only when the capacitor voltage is equal to or exceeds the peak voltage plus a margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If pre-charge resistors are provided for each relay, then inrush current suppression is improved, but cost and weight increase
Solution Approach 1:
The patent merges the pre-charge function into a single resistor shared by all three phases, rather than providing separate pre-charge resistors for each phase. This consolidation reduces the total number of components, thereby reducing weight and cost while maintaining inrush current suppression capability through the shared resistor and capacitor mechanism.
Solution Approach 2:
The single pre-charge resistor is designed to serve all three phases universally. The capacitor couples this single resistor to all three relays, allowing one resistor to perform the pre-charge function for multiple phases, reducing component count while maintaining protective functionality across all phases.
2Weight of stationary object
If pre-charge resistor is provided only for one phase, then cost and weight are reduced, but inrush current may still flow due to unequal voltage swings
Solution Approach 1:
The controller monitors the voltage across the capacitor and uses this feedback to determine when pre-charging is complete. The controller compares the capacitor voltage against the instantaneous phase voltages and only closes all relays when the capacitor voltage exceeds the peak phase voltage plus a margin, ensuring inrush current suppression regardless of which phase has the highest voltage swing.
Solution Approach 2:
The patent dynamically adjusts the closing decision of relays based on the capacitor voltage parameter. Instead of closing relays at fixed time intervals or based on nominal voltage assumptions, the controller continuously monitors the capacitor voltage and adjusts the relay closing timing to ensure the capacitor is sufficiently charged to handle any phase voltage swing, eliminating inrush current risks.
3Productivity
If all relays are closed immediately upon connection, then charging speed is improved, but inrush current flows through the charging device
Solution Approach 1:
The patent implements preliminary action by pre-charging the capacitor through the pre-charge resistor before closing all relays. The controller monitors the capacitor voltage and only closes the remaining relays after the capacitor voltage exceeds the peak phase voltage plus a margin. This preliminary charging action ensures that when all relays are closed, no inrush current will flow, while minimizing the delay before full charging begins.
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 effectively suppresses inrush currents across all phases, reduces costs and weight by using a single pre-charge resistor, and ensures stable charging by equalizing capacitor voltage before closing all relays.
Implementation Method 1
a capacitor which smooths a direct-current voltage supplied from the power factor correction circuit and supplies the smoothed direct-current voltage to the second converter
Implementation Method 2
a power factor correction circuit which improves a power factor of an electric power supplied from the three-phase power supply and boosts a voltage supplied from the three-phase power supply
Implementation Method 3
a pre-charge resistor connected in parallel to the first relay; pre-charges the capacitor via the pre-charge resistor
Implementation Method 4
a first converter which converts the alternating-current power supplied from the three-phase power supply into a direct-current power
Data Source
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AI summary
If sensed a connector (810) as being connected to an inlet (90), an ECU (100) performs pre-charging of a capacitor (CI). When pre-charging of the capacitor (CI) is completed, the ECU (100) closes a relay (RY1), and controls a U-phase boost chopper circuit to boost a voltage (VH) of the capacitor (CI). The ECU (100) closes relays (RY2, RY3) if the voltage (VH) is boosted to a second target voltage (Vtag2).