Series-Parallel DC/DC Converter Control for Input Capacitor Ripple
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High power DC/DC converters in EV charging stations face increased voltage ripple and RMS current requirements for input capacitors due to pulsating power delivery from 1-phase AC supply, necessitating higher capacitance, which is not required in 3-phase operation.
Innovation Solution
A DC/DC converter system with a capacitor bank and a controller that modulates power conversion in two branches oppositely synchronized with AC supply frequency, reducing voltage ripple and RMS current by pulsating power flow through series or parallel connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If 1-phase AC supply is used for front-end converter stage, then the system can operate with single-phase AC voltage supply, but the power delivery to back-end converter stage becomes pulsating at grid frequency, increasing voltage ripple and RMS current requirements for bulk capacitor
Solution Approach 1:
The back-end converter stage is divided into two separate DC/DC converter branches (first branch and second branch). Each branch processes power from one of the two bulk capacitors (C1 and C2) independently. This segmentation allows the pulsating power from 1-phase AC supply to be distributed across two parallel processing paths, reducing the ripple current burden on each individual capacitor while maintaining overall power conversion functionality.
Solution Approach 2:
The patent combines two DC/DC converter branches in parallel configuration, where both branches work simultaneously to convert power from the bulk capacitors to the output. By merging the output of both branches, the system achieves continuous power delivery to the load while the bulk capacitors experience reduced RMS current stress due to the complementary pulsating power distribution between the two branches.
2Reliability
If higher capacitance bulk capacitor is used to handle pulsating power from 1-phase supply, then voltage ripple and RMS current requirements are met, but the capacitor bank size and cost increase
Solution Approach 1:
The bulk capacitor bank is segmented into two separate capacitors (C1 and C2) that are charged during different half-cycles of the AC supply. Each capacitor handles only half of the total power processing duty, which reduces the RMS current and voltage ripple requirements for each individual capacitor compared to using a single large capacitor for the entire pulsating power handling.
Solution Approach 2:
The system utilizes the periodic nature of the AC supply by charging capacitor C1 during positive half-cycles and capacitor C2 during negative half-cycles. This periodic action distributes the power processing burden over time and across two capacitors, allowing each capacitor to be smaller while collectively handling the same average power as a single larger capacitor would require.
3Reliability
If 3-phase AC supply is used for front-end converter stage, then power delivery to back-end converter stage is substantially constant with no significant voltage ripple, but the system cannot operate with single-phase AC voltage supply
Solution Approach 1:
The back-end converter stage is designed with universal functionality to operate with both 1-phase and 3-phase AC supply configurations. The two-branch DC/DC converter architecture with complementary pulsating power processing enables the system to achieve constant power delivery characteristics similar to 3-phase operation when fed from 1-phase supply, while also being capable of direct connection to 3-phase supplies without modification.
Data Source
Figure 1~2
Figure 3(a)~4
Figure 5(a)~6(b)
AI summary
A power conversion system and a respective method are described herein. In one embodiment, the system comprises a capacitor bank including at least a first capacitor and a second capacitor coupled in series, wherein the capacitor bank is connected between a first input terminal and a second input terminal and wherein the first and second capacitors are connected at a center node. The system further comprises an AC/DC converter configured to provide a DC input voltage to the capacitor bank based on an AC voltage provided by the AC supply, and a DC/DC switching converter including a first branch, a second branch, and a switching circuit. The first branch is configured to convert a first voltage buffered by the first capacitor into an first output voltage, and the second branch is configured to convert a second voltage buffered by the second capacitor into a second output voltage. The switching circuit is configured to provide an output voltage based on the first output voltage and the second output voltage. Furthermore, the system comprises a controller configured to generate a plurality of switching signals for the DC/DC switching converter to control the switching operation of the first branch and the second branch of the DC/DC switching converter, such that the power converted by the first branch and the power converted by the second branch are modulated oppositely to each other in synchronization with a frequency of the AC supply.