EV Inverter Bulk Capacitor Voltage Control During Pre-Charging
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Solution Overview
Problem
On-board chargers for electric vehicles face challenges in safely regulating capacitor voltage, particularly during pre-charging and battery-to-grid operations, which can lead to overcharging and potential damage to the capacitor.
Innovation Solution
A system and method that include an AC-DC converter with a bulk capacitor, a DC-DC converter having transformers and a bridge rectifier switch, controlled by controllers to manage the capacitor voltage through pre-charging, battery-to-grid operations, and duty cycle adjustments based on determined voltage setpoints and feedforward terms, ensuring safe and efficient voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitor voltage is regulated during pre-charging and battery-to-grid operations, then the capacitor may become overcharged, but this leads to capacitor damage
Solution Approach 1:
The system performs a pre-charging operation before the main battery-to-grid operation. During pre-charging, the controller gradually increases the duty cycle of the bridge rectifier switch from 0% to 50%, transferring electrical energy from the battery to the bulk capacitor in a controlled manner. This preliminary action prepares the capacitor for the subsequent high-power operation while preventing sudden overcharging that could damage the capacitor.
Solution Approach 2:
The controller continuously monitors the bulk capacitor voltage and adjusts the bridge rectifier switch duty cycle based on the difference between the actual voltage and the voltage setpoint. During pre-charging, when the voltage difference is large, the controller increases the duty cycle to charge the capacitor faster. As the capacitor voltage approaches the setpoint, the duty cycle is reduced to maintain precise voltage control and prevent overcharging.
2Productivity
If the duty cycle is increased to charge the capacitor faster, then the pre-charging time is reduced, but this may cause voltage overshoot and capacitor damage
Solution Approach 1:
The system dynamically adjusts the duty cycle of the bridge rectifier switch during pre-charging based on real-time voltage conditions. The controller ramps the duty cycle from 0% to 50% during pre-charging, and continuously modifies it during battery-to-grid operation based on the voltage difference between the actual capacitor voltage and the setpoint. This dynamic adjustment allows fast charging when needed while preventing voltage overshoot through real-time adaptation.
Solution Approach 2:
The controller operates in periodic cycles, alternating between pre-charging mode and battery-to-grid operation mode. During pre-charging, the duty cycle is increased in a controlled ramp from 0% to 50%. During battery-to-grid operation, the controller periodically adjusts the duty cycle based on voltage feedback to maintain stable operation. This periodic switching between operational phases allows the system to achieve both fast charging and stable voltage control.
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
The solution effectively controls the bulk capacitor voltage, preventing overcharging and enhancing the performance and reliability of on-board chargers during both charging and discharging modes, thereby extending the lifespan of the capacitor and improving operational efficiency.
Implementation Method 1
one or more controllers configured to control an operation of the bridge rectifier switch to control a voltage of the bulk capacitor
Implementation Method 2
one or more transformers having a secondary side connectable to a battery
Data Source
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AI summary
A system includes: an alternating current (AC) to direct current (DC) converter (AC-DC converter) including a bulk capacitor, the AC-DC converter connectable to a line voltage; a DC to DC converter (DC-DC converter) connected to the AC-DC converter, the DC-DC converter including: one or more transformers having a secondary side connectable to a battery, and a bridge rectifier connected to the secondary side of the one or more transformers, the bridge rectifier including a bridge rectifier switch; and one or more controllers configured to control an operation of the bridge rectifier switch to control a voltage of the bulk capacitor.