Ripple Filter Circuit for High-Power-Density Switching Converters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional single-phase power converters suffer from low power density due to the need for large DC bus capacitance to control ripple voltage, and rely on failure-prone electrolytic capacitors.
Innovation Solution
The implementation of a ripple filter circuit with series-connected switches, an inductor, and a storage capacitor, controlled by a circuit that alternately transfers ripple energy from the DC bus capacitor to the storage capacitor and back, using hysteretic control to regulate the ripple voltage, thereby reducing the required DC bus capacitance and avoiding electrolytic capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large DC bus capacitance is used to control ripple voltage, then ripple voltage is reduced, but power density decreases
Solution Approach 1:
The patent segments the DC bus capacitance function into two parts: a small DC bus capacitor and a separate storage capacitor. The storage capacitor handles the bulk of the ripple energy storage and release, while the DC bus capacitor maintains voltage stability. This segmentation allows the DC bus capacitor to be much smaller than conventional designs while still achieving effective ripple voltage control.
Solution Approach 2:
The patent introduces an intermediary circuit consisting of the storage capacitor and associated switching elements that mediates between the rectifier/inverter and the DC bus capacitor. This intermediary absorbs and releases ripple energy, protecting the DC bus capacitor from large current transients and enabling its size to be reduced significantly.
2Object-affected harmful factors
If electrolytic capacitors are used to provide ripple voltage attenuation, then ripple voltage is reduced, but reliability decreases
Solution Approach 1:
The patent changes the type of capacitor used in the DC bus from electrolytic to film or ceramic capacitors. By altering the capacitor technology parameter, the system achieves the same ripple attenuation function with significantly improved reliability and longer service life, eliminating the inherent failures of electrolytic capacitors.
3Speed
If wide bandgap devices are used to increase switching frequency, then passive filter size is reduced, but DC bus capacitor size remains large
Solution Approach 1:
The patent segments the energy buffering function from the voltage stabilization function. The storage capacitor handles energy buffering during high-frequency switching, while the smaller DC bus capacitor focuses on voltage stabilization. This segmentation allows the DC bus capacitor volume to be dramatically reduced even at high switching frequencies enabled by wide bandgap devices.
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 significantly increases power density by minimizing DC bus capacitance, reduces the risk of capacitor failure, and provides a smooth DC bus voltage for efficient power conversion.
Implementation Method 1
an inductor connected to a switching node joining the first and second switches and a storage capacitor between the inductor and one of the DC bus nodes
Implementation Method 2
Switching power converters include switches operated to convert electrical power from one form to another, including DC to AC converters such as switching inverters, AC to DC converters referred to as active rectifiers
Implementation Method 3
the control circuit provides hysteretic control of the absolute value of the inductor current between a first value and a higher second value during transfer of ripple energy between the DC bus capacitor and the storage capacitor
Data Source
AI summary
Disclosed examples include switching power converters, control methods and ripple filter circuits in which first and second switches are connected in series across first and second DC bus nodes, with an inductor connected to a switching node joining the first and second switches and a storage capacitor between the inductor and the second DC bus node. A control circuit operates the switches to alternately transfer ripple energy from a DC bus capacitor of the DC bus circuit through the inductor to the storage capacitor, and then to transfer ripple energy from the storage capacitor through the inductor to the DC bus capacitor to regulate the ripple voltage of the DC bus circuit, and the control circuit provides hysteretic control of the absolute value of the inductor current between a first value and a higher second value during transfer of ripple energy between the DC bus capacitor and the storage capacitor.