Sequential Precharge Control for Electric Power System Startup
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Solution Overview
Problem
The existing electric power systems for vehicles, including fuel cell, electric, and hybrid vehicles, face a delay in startup time due to the precharging of both the secondary battery smoothing capacitor and the high-voltage auxiliary smoothing capacitor, which increases the time required for the drive motor to be operational.
Innovation Solution
An electric power system with a control unit that sequentially precharges the secondary battery smoothing capacitor and then the auxiliary smoothing capacitor, allowing power supply to the drive motor before the auxiliary smoothing capacitor is fully precharged, and includes an electric power generator to reduce the load on the secondary battery, enabling the use of higher voltage auxiliaries and potentially smaller batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If both the secondary battery smoothing capacitor and the auxiliary smoothing capacitor are precharged at startup, then the inrush current is reduced and the system is protected, but the startup time is extended
Solution Approach 1:
The precharging process is segmented into two separate phases: first precharging the secondary battery smoothing capacitor via the secondary battery relay, then precharging the auxiliary smoothing capacitor via the auxiliary relay. This segmentation allows the drive motor to be powered before the auxiliary smoothing capacitor is fully precharged, reducing overall startup time while still providing protection against inrush current.
Solution Approach 2:
The secondary battery smoothing capacitor is precharged in advance before the auxiliary smoothing capacitor. This preliminary action ensures that the drive motor can be powered immediately without waiting for the auxiliary smoothing capacitor to be fully precharged, thus reducing startup time while maintaining system protection.
2Reliability
If the auxiliary smoothing capacitor is precharged before powering the drive motor, then the auxiliary system is protected, but the time required for the drive motor to become operational is increased
Solution Approach 1:
The system operation is segmented into distinct phases: first the secondary battery relay closes to precharge the secondary battery smoothing capacitor and power the drive motor, then the auxiliary relay closes to precharge the auxiliary smoothing capacitor. This segmentation allows the drive motor to become operational before the auxiliary system is fully prepared, improving response speed while maintaining auxiliary system protection.
Solution Approach 2:
The secondary battery smoothing capacitor is precharged in advance before the auxiliary smoothing capacitor. This preliminary action enables the drive motor to be powered immediately, improving the speed at which the drive motor becomes operational while still providing protection to the auxiliary system when it is eventually connected.
3Device complexity
If the secondary battery supplies power to both the drive motor and auxiliary, then the system is simplified, but the battery size must be increased to handle the total load
Solution Approach 1:
The electric power generator is designed to perform multiple functions: it can supply power to the drive motor, supply power to the auxiliary, and charge the secondary battery. This multi-functionality allows the secondary battery to be smaller since it doesn't need to handle the entire load, reducing battery weight while maintaining system simplicity through centralized control.
Data Source
AI summary
An electric power system includes a secondary battery configured to supply electric power to a drive motor, configured to generate driving force of a vehicle, and an auxiliary having an auxiliary smoothing capacitor, a secondary battery relay configured to open or close an electrical contact between the secondary battery and the drive motor, a secondary battery smoothing capacitor connected between the secondary battery relay and the drive motor, an auxiliary relay configured to open or close an electrical contact between the secondary battery and the auxiliary, and a control unit configured to control a switching operation of each of the secondary battery relay and the auxiliary relay. The control unit is configured to, at startup of the vehicle, precharge the secondary battery smoothing capacitor by closing the secondary battery relay and then precharge the auxiliary smoothing capacitor by closing the auxiliary relay.