EV Converter Control for Capacitor Overvoltage Limp-Home
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Solution Overview
Problem
Electric vehicles with a single motor-generator and control unit face difficulties in performing limp-home control if the control unit malfunctions, and abnormal voltage increases in the smoothing capacitor during regenerative power recovery can lead to unrecoverable charge and overvoltage protection, preventing limp-home control.
Innovation Solution
A control apparatus with dual motor-generators and redundant control units that monitor and control the smoothing capacitor voltage, performing switching operations to prevent abnormal voltage increases and enable limp-home control even if one control unit fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single control unit is used to control the motor-generator, then device complexity is reduced, but reliability deteriorates because the system cannot perform limp-home control if the control unit malfunctions
Solution Approach 1:
The control unit is divided into two independent control units (first control unit and second control unit), each capable of independently controlling the motor-generator. This segmentation allows the system to maintain limp-home control capability even if one control unit malfunctions, as the other control unit can take over.
Solution Approach 2:
The system incorporates a redundant control unit as a backup before any malfunction occurs. This beforehand cushioning ensures that if the primary control unit fails, the system can immediately switch to the backup control unit and continue performing limp-home control, preventing complete system failure.
2Use of energy by moving object
If regenerative power recovery is performed during vehicle traveling, then energy efficiency is improved, but harmful factors increase due to abnormal voltage increases in the smoothing capacitor that can prevent limp-home control
Solution Approach 1:
The control units continuously monitor the voltage across the smoothing capacitor during regenerative power recovery. When the voltage exceeds a predetermined threshold, the control units detect this feedback signal and immediately switch off the voltage converter, preventing further voltage increase and eliminating the harmful overvoltage condition.
Solution Approach 2:
The control units are configured to switch off the voltage converter in advance when voltage threshold is approached, preventing the harmful overvoltage condition from developing. This preliminary anti-action stops the regenerative power recovery process before it can cause dangerous voltage levels that would trigger overvoltage protection.
Data Source
AI summary
A second control unit performs a switching control task of repeatedly switching between an on state and an off state of an upper-arm switching device of a voltage converter in response to determination that a monitored terminal voltage across a smoothing capacitor is not lower than or equal to an anomaly determination threshold during failure of a first control unit. The second control unit determines whether the switching control task causes the monitored terminal voltage across the smoothing capacitor to be lower than or equal to the anomaly determination threshold. The second control unit controls, in response to determination that the switching control task causes the monitored terminal voltage across the smoothing capacitor to be lower than or equal to the anomaly determination threshold, at least one motor-generator to perform a limp-home control task of the electric vehicle.