Electric Machine Voltage Control During Traction Battery Failure
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Solution Overview
Problem
The existing methods for controlling the activation of an electric machine in voltage control mode in a traction network of an electric or hybrid motor vehicle are not robust, as precharging may fail, leading to voltage drops and discharging of capacitors due to limited equivalent capacitance when the traction battery fails.
Innovation Solution
A method involving precharging capacitors using a precharging means, activating the electric machine in voltage control mode at a predetermined threshold voltage, gradually increasing the setpoint voltage to a target value, and deactivating precharging when the network voltage reaches or exceeds this target, ensuring reliable operation and minimizing voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If precharging is performed using the traction battery or DC-to-DC converter before activating the electric machine in voltage control mode, then the voltage operating range of the electric machine and DC-to-DC converter is guaranteed, but the method is not robust because any current draw may cause voltage drops and discharge of the precharged capacitors due to limited equivalent capacitance
Solution Approach 1:
The patent applies preliminary action by precharging the capacitors before activating the electric machine in voltage control mode. This ensures that the capacitors are already charged to the required voltage level before the electric machine starts drawing current, thereby preventing voltage drops and maintaining network stability during the transition to voltage control mode.
Solution Approach 2:
The patent implements beforehand cushioning by maintaining the precharged state of the capacitors as a buffer against voltage fluctuations. The precharged capacitors act as an energy reservoir that cushions the electrical network against sudden voltage drops when the electric machine or DC-to-DC converter is activated, ensuring continuous stable operation.
2Reliability
If the contactors of the traction battery are kept open and the electric machine is placed in voltage control mode, then the electric machine becomes a current generator to regulate voltage, but the equivalent capacitance of the network is limited making the system vulnerable to voltage drops
Solution Approach 1:
The patent applies preliminary action by precharging the capacitors before the electric machine is activated in voltage control mode. This ensures that the capacitors are already charged to the required voltage level, providing an immediate energy buffer that compensates for the limited equivalent capacitance in the network when the traction battery contactors are open.
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 method provides precise and reliable control of the electric machine in voltage control mode, reducing voltage drops and ensuring effective operation by maintaining network stability during electric machine activation.
Implementation Method 1
a first step of precharging capacitors present in the electrical network using a precharging means
Implementation Method 2
the electric machine delivering an electric current with a setpoint voltage corresponding to an initial setpoint value equal to the voltage of the electrical network
Data Source
AI summary
A method for controlling the activation of an electric machine in voltage control mode for an electrical network of a motor vehicle following a failure of a traction battery present in a traction network of the vehicle. The traction network includes the traction battery, the electric machine, an inverter and a DC-to-DC converter connecting the traction battery to an onboard network of said motor vehicle. The method includes a step of precharging capacitors present in the electrical network and a step of activating the electric machine in voltage control mode for the electrical network. The activation of the electric machine in voltage control mode is activated before the deactivation of precharging.