On-Board Charger Variable DC-Link Control for Low-Voltage Efficiency
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Solution Overview
Problem
Existing vehicle on-board chargers (OBCs) are inefficient when connected to low AC grid voltages due to fixed DC-Link voltage designs, leading to significant efficiency losses as they require large voltage conversions, which are not optimal for varying AC and battery voltages.
Innovation Solution
The OBC incorporates a processor-controlled system that adjusts the DC-Link voltage between a first and second setpoint based on battery voltage, optimizing voltage conversion by using a capacitor and power factor correction circuit to minimize unnecessary conversions and maximize efficiency across different input and output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fixed DC-Link voltage is used in the on-board charger, then the charger can maintain stable operation, but efficiency losses increase significantly when connected to low AC grid voltages due to large voltage conversions
Solution Approach 1:
The patent implements a dynamic DC-Link voltage adjustment mechanism where the DC-Link voltage is no longer fixed but varies according to the AC input voltage and battery charging requirements. The controller continuously monitors input voltage conditions and adjusts the DC-Link voltage accordingly, transitioning from a static to a dynamic system that adapts to different operating conditions, thereby reducing voltage conversion losses while maintaining operational stability.
Solution Approach 2:
The patent changes the operating parameter of DC-Link voltage from a constant value to a variable value that depends on the AC input voltage level. By adjusting the DC-Link voltage parameter dynamically based on input conditions, the system optimizes the voltage conversion ratio across different operating points, minimizing energy losses while maintaining adaptability to various AC grid voltages and battery charging requirements.
2Productivity
If the DC-Link voltage is adjusted dynamically based on battery voltage, then charging efficiency improves, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The patent implements a feedback control mechanism where the controller monitors the battery voltage and AC input voltage, then adjusts the DC-Link voltage accordingly. This closed-loop feedback system automatically optimizes charging efficiency by continuously adapting the DC-Link voltage to match the current operating conditions, eliminating the need for complex manual control while improving productivity through automated voltage optimization.
3Adaptability or versatility
If a fixed DC-Link voltage design is used, then the charger structure remains simple, but the charger cannot optimize voltage conversion for varying AC input voltages
Solution Approach 1:
The patent transforms the static DC-Link voltage design into a dynamic system that automatically adapts to different AC input voltage standards (such as 110V or 220V). The controller detects the input voltage level and adjusts the DC-Link voltage accordingly, enabling the charger to maintain optimal efficiency across different regional voltage standards while keeping the physical structure simple and unchanged.
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
This approach enhances efficiency by reducing voltage conversion losses, especially at low AC grid voltages, and allows for worldwide compatibility by dynamically adjusting the DC-Link voltage in response to battery conditions, thereby improving charging efficiency and adaptability.
Implementation Method 1
a rectifier for converting an alternating current (AC) voltage from an external power supply to a direct current (DC) voltage
Implementation Method 2
A capacitor is coupled to the rectifier to provide a DC-Link voltage
Implementation Method 3
A converter is coupled to the capacitor to adjust the DC-Link voltage and is adapted to couple to a battery
Data Source
AI summary
An on-board charger is provided with a first stage for converting an alternating current (AC) voltage from an external power supply to a direct current (DC) voltage. A capacitor is coupled to the first stage to receive the DC voltage and to provide a DC-Link voltage. A second stage is coupled to the capacitor to boost the DC-Link voltage and to supply the boosted DC-Link voltage to charge a battery. A processor is programmed to adjust the DC-Link voltage between a first setpoint and a second setpoint based on a battery voltage value.