Split Resonant Inductor for Common Mode Noise Reduction
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Solution Overview
Problem
Isolated DC/DC converters experience common mode noise due to unbalanced currents through inter-winding capacitances of the isolation transformer, particularly when a discrete resonant choke is used, which existing solutions do not adequately address.
Innovation Solution
A resonant DC/DC converter design featuring a primary and secondary circuit with a split resonant inductor and capacitor, where the split resonant inductor shares a common magnetic flux path and has an equivalent or optimized inductance ratio, and a synchronous rectifier circuit to minimize stepwise voltage changes and capacitive currents, thereby reducing common mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a discrete resonant choke is used in the converter, then the converter can achieve resonant operation and improved efficiency, but common mode noise increases due to unbalanced currents through inter-winding capacitances
Solution Approach 1:
The resonant inductor is divided into two separate windings (Lr1 and Lr2) with equal inductance values. This segmentation allows the unbalanced capacitive currents to be distributed symmetrically, causing them to cancel each other out and reduce common mode noise while maintaining resonant operation efficiency.
Solution Approach 2:
The patent uses symmetric asymmetry - by making the two inductor windings identical in inductance value and configuration, it creates a balanced structure that counteracts the inherent asymmetry in inter-winding capacitances, thereby reducing common mode noise generated during switching operation.
2Speed
If the primary center point voltage has stepwise voltage changes with high dv/dt, then the converter can respond dynamically to load changes, but capacitive currents through inter-winding capacitances increase causing oscillations
Solution Approach 1:
The primary center point voltage is divided into two equal voltage transitions through the split inductor windings. Each winding handles half of the voltage change, reducing the dv/dt across each inter-winding capacitance and minimizing the resulting capacitive currents and oscillations.
Solution Approach 2:
The patent maintains equipotential symmetry by ensuring both inductor windings have equal inductance values and are subjected to equal voltage transitions. This symmetry ensures that capacitive currents flowing through the inter-winding capacitances are equal and opposite, causing them to cancel out and prevent oscillations.
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
The solution effectively minimizes common mode noise by stabilizing the primary center point voltage and reducing capacitive currents, resulting in low common mode voltage between the primary and secondary circuits, even when a discrete resonant choke is employed.
Implementation Method 1
The inter-winding capacitances typically define a capacitive coupling between the primary and secondary circuits of the converter
Implementation Method 2
an isolation transformer with at least one primary and one secondary winding
Implementation Method 3
a resonant tank having a resonant capacitor and a split resonant inductor with two separate windings
Data Source
AI summary
A resonant DC/DC power converter is provided with isolated primary and secondary circuits. The primary circuit includes at least four switches as first and second pairs in a bridge configuration, an isolation transformer having at least one primary and at least one secondary winding, and a resonant tank including a resonant capacitor and a split resonant inductor having two separate windings. In one embodiment, the split resonant inductor windings are substantially identical. Synchronous switching of diagonally opposed switch pairs in the bridge configuration thereby produces a center point voltage of the primary transformer winding is substantially free of stepwise voltage changes.