Inverter Bulk Capacitor Voltage Control During EV Pre-Charge
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Solution Overview
Problem
Existing on-board chargers for electric vehicles face challenges in efficiently controlling capacitor voltage, particularly during pre-charging and battery-to-grid operations, which can lead to overcharging and potential damage to capacitors.
Innovation Solution
A system comprising an AC-DC converter with a bulk capacitor, a DC-DC converter with transformers and a bridge rectifier, and controllers that manage the bridge rectifier switch to control the bulk capacitor voltage. The controllers determine a voltage setpoint and a feedforward term to precisely control the capacitor voltage during pre-charging and battery-to-grid operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the capacitor voltage is not controlled during pre-charging and battery-to-grid operations, then the system operation is simplified, but the capacitor may be overcharged and damaged
Solution Approach 1:
The controller implements feedback control by continuously monitoring the bulk capacitor voltage and adjusting the bridge rectifier switch duty cycle to maintain voltage within safe operating limits. The controller determines a voltage setpoint and compares actual voltage against this setpoint, dynamically adjusting the switching duty cycle to prevent overcharging while ensuring reliable capacitor operation during pre-charging and battery-to-grid modes.
2Productivity
If the bridge rectifier switch duty cycle is rapidly increased during pre-charging, then the capacitor charges faster, but the capacitor may be damaged due to excessive voltage
Solution Approach 1:
The system employs dynamic control of the bridge rectifier switch duty cycle during pre-charging operations. Rather than using a fixed or rapidly increasing duty cycle, the controller dynamically adjusts the duty cycle based on real-time capacitor voltage measurements, ensuring the capacitor charges at an optimal rate while maintaining voltage within safe limits. This dynamic adjustment prevents both undercharging and overcharging conditions.
Solution Approach 2:
The controller performs preliminary voltage assessment before initiating full charging operations. By determining a voltage setpoint and evaluating the current capacitor state beforehand, the controller prepares appropriate control parameters that prevent excessive voltage application from the outset, ensuring safe and efficient charging from the beginning of the pre-charging sequence.
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 system effectively regulates the bulk capacitor voltage, preventing overcharging and ensuring safe operation during both pre-charging and battery-to-grid modes, thereby extending the lifespan of the capacitors and improving the overall efficiency of the on-board charger.
Implementation Method 1
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
Implementation Method 2
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
Implementation Method 3
a bridge rectifier connected to the secondary side of the one or more transformers, the bridge rectifier including a bridge rectifier switch
Data Source
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.