Contactor Pre-Charge Control Using a Bi-Directional DC/DC Converter
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Solution Overview
Problem
Existing contactor control systems in electric and hybrid vehicles experience high energy losses and wear due to the high current peaks when connecting and disconnecting the high voltage battery from the DC-link capacitor, which is not adequately addressed by current pre-charge and discharge methods.
Innovation Solution
A bi-directional DC/DC-converter is used to pre-charge the DC-link capacitor to a predefined voltage from a low voltage energy storage before connecting the high voltage battery, and to discharge the capacitor to the low voltage storage when disconnected, minimizing wear and energy loss by maintaining similar voltages on both sides of the switching member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a pre-charge circuit with a current limiting resistor is used to pre-charge the DC-link capacitor, then the current peak through the contactor is reduced, but energy is lost as heat in the resistor and the pre-charge process takes time due to the RC-time constant
Solution Approach 1:
The system performs preliminary action by pre-charging the DC-link capacitor to a voltage close to the high voltage battery voltage before the contactor closes. This is achieved through a bi-directional DC/DC converter that can charge the capacitor in advance, reducing both the current peak and energy loss compared to traditional resistor-based pre-charge circuits.
Solution Approach 2:
The invention changes the voltage parameter of the DC-link capacitor dynamically. The bi-directional DC/DC converter adjusts the capacitor voltage to match the battery voltage before contactor closure, and can also discharge the capacitor back to the battery when the contactor opens, thereby minimizing energy loss and avoiding the need for dissipative resistor-based pre-charge circuits.
2Loss of energy
If the DC-link capacitor is discharged through a discharge resistor, then the capacitor is completely discharged, but all the stored energy is converted to heat and lost
Solution Approach 1:
Instead of discarding the energy stored in the DC-link capacitor as heat through a discharge resistor, the system recovers this energy by using a bi-directional DC/DC converter to transfer it back to the high voltage battery. This principle of recovering and reusing energy eliminates the energy loss while maintaining safe discharge functionality.
Solution Approach 2:
The invention converts the potentially harmful effect of needing to dissipate capacitor energy as heat into a beneficial process of energy recovery. The bi-directional DC/DC converter transforms the discharge process from an energy-wasting operation into an energy-recharging operation, benefiting the overall system by replenishing the battery.
3Loss of energy
If a bi-directional DC/DC-converter is used to pre-charge and discharge the DC-link capacitor, then energy losses are minimized and component wear is reduced, but the device complexity increases
Solution Approach 1:
The bi-directional DC/DC converter serves multiple functions: it acts as a pre-charge circuit before contactor closure, as a discharge circuit after contactor opening, and can also function as a power management device for the high voltage battery. This multi-functionality reduces the need for separate dedicated pre-charge and discharge circuits, thereby limiting the increase in overall system complexity.
Solution Approach 2:
The invention merges the pre-charge and discharge functions into a single bi-directional DC/DC converter unit. Instead of having separate pre-charge circuits with resistors and separate discharge circuits with resistors, both functions are combined in one convertible device that can operate in both charging and discharging modes, simplifying the overall circuit architecture.
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 energy losses and wear on the switching member by minimizing voltage differences during pre-charge and discharge, allowing for more efficient energy transfer and prolonged component lifespan.
Implementation Method 1
A bi-directional DC/DC-converter is used to pre-charge the DC-link capacitor to a predefined voltage from a low voltage energy storage before connecting the high voltage battery
Implementation Method 2
to discharge the capacitor to the low voltage storage when disconnected
Implementation Method 3
The capacitor is adapted to reduce and absorb transients at the high voltage load caused by e.g. an PWM inverter that drives the electric motor, and to stabilize the voltage at the high voltage load
Data Source
AI summary
A contactor control system includes a switching member, a high voltage load, a high voltage energy storage, a bi-directional DC/DC-converter operatively connected to the switching member, a high-voltage capacitor operatively connected to the high-voltage load, and a low voltage energy storage operatively connected to the bi-directional DC/DC-converter, wherein the switching member is adapted to connect and disconnect the high voltage energy storage to and from the high voltage load, where the bi-directional DC/DC-converter is adapted to pre-charge the high-voltage capacitor to a predefined voltage value from the low voltage energy storage before the switching member is closed and adapted to discharge the high-voltage capacitor to the low voltage energy storage when the switching member has been opened. The advantage of the invention is that a DC-link capacitor can be charged from and discharged to a low voltage battery by using a bi-directional DC/DC-converter. Energy losses can thus be minimized.