Adaptive DC Link Voltage Control for EV Charging Converters
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Solution Overview
Problem
Existing two-stage power converters for electric vehicle charging face inefficiencies at low output voltages due to fixed DC link voltage, leading to increased charging time and conduction losses, as they struggle to adaptively control the DC link voltage based on output conditions.
Innovation Solution
A controller system for two-stage power converters that dynamically adjusts the DC link voltage using phase-shift modulation, allowing the first stage to generate a variable DC link voltage responsive to output conditions, thereby improving charging efficiency, especially at low output voltages, by integrating PFC and DAB converters with adaptive power control routines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed DC link voltage is used in two-stage power converters, then the control system is simpler, but charging efficiency deteriorates at low output voltages due to increased conduction losses
Solution Approach 1:
The patent implements dynamic DC link voltage adjustment by coupling the first-stage PFC controller with the second-stage DC-DC controller. The DC link reference voltage is dynamically modified based on the actual output voltage feedback, enabling the system to adapt to varying output conditions and minimize conduction losses across different operating points.
Solution Approach 2:
The system changes the DC link voltage parameter dynamically based on output conditions. By adjusting the DC link reference voltage according to the actual output voltage, the system optimizes the operating point of power devices, reducing conduction losses particularly at low output voltages where circulation currents are significant.
2Productivity
If higher charging power is used to reduce charging time, then charging speed improves, but conduction losses increase at low output voltages
Solution Approach 1:
The system dynamically adjusts the DC link voltage based on real-time output voltage feedback. This enables the power converter to maintain optimal operating conditions across different charging power levels and output voltages, reducing conduction losses while preserving charging speed capability.
Solution Approach 2:
The patent implements a feedback mechanism where the actual output voltage is continuously monitored and used to modify the DC link reference voltage. This closed-loop control enables the system to respond to output conditions and optimize efficiency without sacrificing charging power capability.
3Loss of energy
If the DC link voltage is varied to improve charging efficiency at low output voltages, then conduction losses are reduced, but the control complexity increases
Solution Approach 1:
The patent merges the control functions of the first-stage PFC and second-stage DC-DC converters by coupling their controllers. The DC link reference voltage generation is integrated with the output voltage feedback from the second stage, creating a unified control system that achieves dynamic voltage adjustment without requiring entirely separate control architectures.
Solution Approach 2:
The control system performs multiple functions: it maintains power factor correction in the first stage, regulates the DC link voltage dynamically, and controls the output voltage of the second stage. This multi-functional approach consolidates control tasks and manages complexity through integrated design.
4Device complexity
If first-stage control is isolated from the second stage output, then the control architecture is simpler, but adaptive power control capability is reduced
Solution Approach 1:
The DC link reference voltage serves as an intermediary between the first-stage PFC controller and the second-stage DC-DC controller. By modifying this intermediate parameter based on second-stage output feedback, the system achieves adaptive control capability while maintaining a relatively simple control architecture through a well-defined interface.
Solution Approach 2:
The patent applies local quality by making the DC link voltage reference adaptive based on local output conditions. The control system maintains simplicity in the overall architecture while introducing adaptability at the critical DC link interface, where the modification of reference voltage provides the necessary coupling for adaptive power control.
Data Source
AI summary
A two-stage power converter has a Power-Factor Converter (PFC) and a Dual Active Bridge (DAB) converter connected together by a DC link voltage. The DAB converter outputs a battery voltage with a battery current. A PFC controller divides a reference power constant by the battery voltage to get a battery current reference that is multiplied by a constant and compared to the DC link voltage to adjust Pulse-Width-Modulation (PWM) control signals to the PFC. The reference power constant is compared to the battery current during Constant-Power mode to cause a DAB controller to modulate duty ratio and phase difference between primary and secondary-side PWM control signals to the DAB converter. The DAB converter duty ratio and phase difference are modulated by comparing the battery current to a battery current limit during Constant-Current mode and by comparing the battery voltage to a battery voltage limit during Constant-Voltage mode.