DC Link Current Ripple Reduction via Phase Shifted Converter Control
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Solution Overview
Problem
Current DC-DC and DC-AC power conversion systems in electric and hybrid vehicles face challenges in reducing DC link current ripple, leading to larger and less efficient DC link capacitors, particularly in high-temperature automotive applications.
Innovation Solution
A drive system with a DC-DC converter and DC-AC converter is controlled using a control system that adjusts operational parameters such as modulation methods, phase shifts, switching frequencies, and duty cycles to minimize current ripple across the DC link capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC link capacitor is used to absorb current ripple in DC-DC and DC-AC power conversion systems, then the system can operate reliably, but the capacitor becomes bulky and its life is reduced due to high ripple current
Solution Approach 1:
The patent converts the harmful ripple current into a beneficial effect by using the DC-DC converter to generate ripple current that is intentionally out of phase with the inverter's ripple current. This harmful ripple is transformed into a useful cancellation mechanism, where the converter's ripple current neutralizes the inverter's ripple current, thereby reducing the net ripple current through the capacitor and extending its life while maintaining system reliability
Solution Approach 2:
The patent changes the operating parameters of the DC-DC converter, specifically adjusting its duty cycle and switching frequency, to optimize the ripple current cancellation effect. By dynamically adjusting these parameters, the system maintains effective ripple reduction across varying operating conditions, thereby reducing capacitor stress without compromising system reliability
2Reliability
If the DC link capacitor is sized for maximum ripple current, then it can handle peak conditions, but its life is reduced due to continuous high ripple current exposure
Solution Approach 1:
The patent transforms the problematic ripple current that would normally degrade the capacitor into a beneficial cancellation mechanism. The DC-DC converter is controlled to produce ripple current that opposes and reduces the net ripple current through the capacitor, converting what would be harmful continuous stress into a protective effect that extends capacitor life while maintaining peak current handling capability
3Weight of stationary object
If prior art methods use bang-bang controller to reduce ripple current, then capacitor size is reduced, but DC voltage ripple increases
Solution Approach 1:
The patent employs feedback control mechanisms to monitor and adjust the DC-DC converter's operation, optimizing the ripple current cancellation while maintaining DC voltage stability. The control system continuously adjusts the converter's duty cycle and switching frequency based on measured ripple current and DC voltage levels, ensuring that capacitor size is reduced without causing excessive DC voltage ripple
Solution Approach 2:
The patent dynamically adjusts the DC-DC converter's operating parameters, including duty cycle and switching frequency, to optimize the balance between ripple current reduction and DC voltage stability. By continuously tuning these parameters based on system conditions, the system achieves capacitor minimization while preventing excessive DC voltage ripple
4Weight of stationary object
If two inverters are used to cancel current ripple, then DC link current ripple is reduced, but the system requires motor with segmented windings or two separate motors
Solution Approach 1:
The patent extracts the ripple current cancellation function from the inverter system and implements it in the DC-DC converter. Instead of requiring two inverters or modified motor windings, the solution places the active ripple compensation functionality in the DC-DC converter, which already exists in the system for voltage boosting. This reduces system complexity while achieving the same ripple reduction effect
Solution Approach 2:
The patent makes the DC-DC converter perform multiple functions: voltage boosting and ripple current cancellation. By utilizing the existing DC-DC converter for dual purposes, the system avoids the complexity of adding specialized ripple cancellation hardware or modifying the motor structure, achieving ripple reduction through a multi-functional approach
Data Source
AI summary
A system and method for operating a drive system coupleable to one or more DC and AC electrical ports is disclosed. The drive system includes a DC link, at least one DC-DC converter, at least one DC-AC converter, a DC link capacitor, and a control system configured to control operation of one or more of the at least one DC-DC converter and the at least one DC-AC converter relative to one another based on operational parameters thereof. In controlling operation of one or more of the at least one DC-DC converter and the at least one DC-AC converter, the control system controls at least one of a switching frequency of the at least one DC-DC converter, a switching frequency of the at least one DC-AC converter, a DC-DC converter carrier signal phase, a DC-AC converter carrier signal phase, and a duty cycle of the at least one DC-DC converter.