Intermediate Circuit Capacitor Precharge for EV Startup Reliability
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Solution Overview
Problem
Electrically driven vehicles face issues with damage to switches and relays due to high initial charging currents when the intermediate circuit capacitor is charged directly from the traction battery, and existing solutions like bidirectional DC/DC converters are ineffective in boost operation faults, leading to vehicle startup failures.
Innovation Solution
A method and device that control a charging means to gradually charge the intermediate circuit capacitor via an external energy source, using a signal to close switches only when the capacitor is sufficiently charged, and utilize a bidirectional DC/DC converter to supply energy between the high-voltage and low-voltage grids, allowing for alternative charging even in the absence of a pre-charging circuit or defective DC/DC converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the intermediate circuit capacitor is charged directly from the traction battery by closing the switches, then the charging speed is high and the vehicle can be started quickly, but the high initial charging current causes damage to the switches and relay contacts
Solution Approach 1:
The patent applies preliminary action by pre-charging the intermediate circuit capacitor through a pre-charging circuit (containing a pre-charging resistor and auxiliary relay) before closing the main switches. This preliminary charging step reduces the voltage difference between the capacitor and battery, thereby limiting the initial charging current and preventing damage to the switches and relay contacts when the main connection is established.
Solution Approach 2:
The patent uses a pre-charging circuit as an intermediary element between the traction battery and the intermediate circuit capacitor. This intermediary circuit, consisting of a pre-charging resistor and auxiliary relay, mediates the charging process by providing a controlled path for current flow that limits the initial surge current, thus protecting the main switches and relay contacts from damage.
2Object-affected harmful factors
If a pre-charging circuit is used to charge the intermediate circuit capacitor at reduced current, then the switches are protected from damage, but the charging process takes longer and delays vehicle startup
Solution Approach 1:
The pre-charging circuit performs preliminary action by charging the intermediate circuit capacitor before the main switches are closed. This preliminary charging step, while taking some time, is necessary to protect the switches from damage by limiting the initial current surge.
Solution Approach 2:
The pre-charging circuit acts as an intermediary that balances the conflicting requirements of switch protection and charging speed. By providing a controlled charging path with limited current, it protects the switches while still enabling the capacitor to be charged to a sufficient voltage level for vehicle startup.
3Adaptability or versatility
If a bidirectional DC/DC converter is used to charge the intermediate circuit capacitor from the low-voltage grid, then the switches are protected and the system is more versatile, but the converter may fail in boost operation and prevent vehicle startup
Solution Approach 1:
The patent applies universality by implementing multiple charging paths for the intermediate circuit capacitor: the traditional pre-charging circuit, the bidirectional DC/DC converter, and the innovative use of the charging means originally intended for battery charging. This multi-functional approach allows the system to adapt to different operating conditions and fault scenarios, maintaining versatility while improving reliability.
Solution Approach 2:
The patent applies beforehand cushioning by providing alternative charging paths that can compensate for potential failures of any single charging method. The control device monitors the status of different charging paths and can switch to alternative methods if one fails, cushioning against the impact of individual component failures and maintaining vehicle startup capability.
4Object-affected harmful factors
If the charging means is controlled to charge the intermediate circuit capacitor via an external energy source, then the capacitor can be charged safely without high currents, but additional control complexity is required
Solution Approach 1:
The patent applies universality by making the charging means, originally designed for charging the traction battery, also capable of charging the intermediate circuit capacitor. This multi-functional use of existing hardware reduces the need for additional dedicated components while still providing controlled charging capability.
Solution Approach 2:
The patent uses feedback control by having the control device monitor the voltage or charge state of the intermediate circuit capacitor and adjust the charging current accordingly. The control device emits control signals to the charging means based on the determined capacitor state, ensuring safe charging without excessive current while managing the control complexity through intelligent regulation.
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
Enables safe and efficient charging of the intermediate circuit capacitor without high currents, allowing the vehicle to be restarted and operated even in case of pre-charging circuit or DC/DC converter faults, ensuring quick readiness and reduced maintenance needs.
Implementation Method 1
In an inverter, also connected to the high-voltage grid, there is a comparatively large intermediate circuit capacitor, or capacitor
Implementation Method 2
the bidirectional DC/DC converter is arranged between the high-voltage grid and a low-voltage grid or a 12-volt grid of the vehicle electrical system. Energy is drawn from the low-voltage grid, preferably from a 12 V battery
Data Source
AI summary
A method (400) for operating an electrically driven vehicle (300), comprising the following steps: emitting a signal for controlling (420) a connectable charging means (160) for charging an intermediate circuit capacitor (140); determining (440) a voltage at an intermediate circuit capacitor (140) or of the charge thereof; emitting a signal for closing (460) the switches (130) for connecting the traction battery (150) to the high-voltage grid (110) as a function of the determined voltage or charge.