Three-Phase Charger Control for Single-Resistor Pre-Charge
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Solution Overview
Problem
Existing vehicle-mounted charging devices face challenges in suppressing inrush currents when connected to three-phase power supplies, leading to increased costs and weight due to the need for pre-charge resistors for each relay, and voltage imbalances between phase power supplies can cause inrush currents even with pre-charging approaches.
Innovation Solution
A charging device with a power factor correction circuit and a capacitor, where a pre-charge resistor is connected in parallel to one relay, and a controller manages the relays and power factor correction circuit to pre-charge the capacitor and boost the voltage to a target level, ensuring balanced voltage across phases and reducing inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If pre-charge resistors are provided for each relay in the charging device, then inrush current can be suppressed, but cost and weight increase
Solution Approach 1:
The patent merges the pre-charge function into a single shared resistor that serves all three phase relays simultaneously. Instead of having separate pre-charge resistors for each relay, one resistor is used to pre-charge all phases before the relays are closed, thereby suppressing inrush current while reducing the total number of components and overall weight.
Solution Approach 2:
The single pre-charge resistor performs a universal function across all three phases. It is designed to pre-charge multiple phases sequentially or simultaneously, making one component serve multiple purposes that would traditionally require three separate components, thus reducing cost and weight.
2Weight of stationary object
If pre-charge resistor is provided only for one relay to reduce cost and weight, then voltage swings between phase power supplies cause inrush current when relays are closed
Solution Approach 1:
The patent applies preliminary action by pre-charging all three phases through the single pre-charge resistor before closing the relays. The controller manages the timing to ensure each phase is pre-charged to an appropriate voltage level prior to relay closure, preventing inrush current even though only one resistor is used. This preliminary pre-charging action addresses the voltage swing issue that would otherwise cause inrush current.
Solution Approach 2:
The system dynamically controls the pre-charging process by monitoring voltage levels and adjusting the pre-charge duration for each phase. The controller adapts the pre-charge timing and sequence based on the actual voltage swings of different phases, ensuring that all phases are properly pre-charged before relay closure, thereby preventing inrush current under varying operating conditions.
3Device complexity
If pre-charge resistor is provided only for one relay to reduce cost and weight, then device complexity is reduced, but inrush current generation cannot be fully suppressed
Solution Approach 1:
The single pre-charge resistor acts as an intermediary component that mediates the power flow from the power supply to all three phases. The controller serves as another intermediary that coordinates the pre-charge process and relay closure timing. This intermediary approach allows one resistor to effectively manage power distribution across all phases, reducing device complexity while still suppressing inrush current through intelligent control.
Solution Approach 2:
The system incorporates feedback control where the controller monitors the voltage levels of all three phases during the pre-charge process. Based on this feedback information, the controller adjusts the pre-charge duration and timing for each phase, and determines the optimal moment to close the relays. This feedback mechanism ensures that inrush current is suppressed effectively despite using only one pre-charge resistor, while keeping the device complexity low.
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 configuration effectively suppresses inrush currents while reducing costs and weight by providing a pre-charge resistor for only one relay, ensuring balanced voltage across phases and preventing inrush currents when all relays are closed.
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
three relays for switching the connection and disconnection between the respective phase power supplies included in the three-phase power supply
Data Source
AI summary
If sensed a connector as being connected to an inlet, an ECU performs pre-charging of a capacitor. When pre-charging of the capacitor is completed, the ECU closes a relay, and controls a U-phase boost chopper circuit to boost a voltage of the capacitor. The ECU closes relays if the voltage is boosted to a second target voltage.