Full Bridge LLC Converter CM EMI Noise Reduction
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Solution Overview
Problem
LLC resonant converters generate significant common mode (CM) electromagnetic interference (EMI), which is a drawback in various applications, including photovoltaic systems and solar microinverters.
Innovation Solution
A full bridge LLC resonant converter design that includes a capacitor connecting the input node of the full bridge circuit with respect to the resonant tank circuit to the output node of the transformer, creating an additional noise loop that cancels out the CM noise by adjusting the loop impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a full bridge resonant converter is used to achieve high power and high power density, then the converter can handle high primary currents, but it generates large common mode electromagnetic interference
Solution Approach 1:
The patent utilizes the harmful common mode electromagnetic interference generated by the full bridge resonant converter to create a beneficial effect. By intentionally designing a secondary noise loop that replicates the characteristics of the original noise loop, the converter transforms the harmful EMI into a useful noise cancellation mechanism, reducing the overall electromagnetic interference by more than 20 dBs at the switching frequency
Solution Approach 2:
The patent introduces asymmetry in the circuit configuration by adding a capacitor connecting the input node of the full bridge circuit to the output node of the transformer. This asymmetric modification creates an additional noise loop with specific impedance characteristics that are different from the original symmetric full bridge configuration, enabling effective noise cancellation
2Device complexity
If a half bridge resonant converter is used to reduce the number of switches, then the switch count is halved, but the current requirement doubles
Solution Approach 1:
Instead of accepting the high current requirement as a necessary trade-off for using a half bridge converter, the patent inverts the approach by using a full bridge configuration and adding the capacitor-based noise cancellation circuit. This inversion allows the system to maintain lower primary currents while still achieving the desired reduction in switch count through the EMI reduction technique
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 design effectively reduces CM EMI noise by more than 20 dBs at the switching frequency, improving the converter's performance and reducing electromagnetic interference.
Implementation Method 1
a capacitor connecting an input node of the full bridge circuit with respect to the resonant tank circuit to an output node of the transformer
Data Source
AI summary
A full bridge LLC resonant converter can include: a full bridge circuit including a first input node and a second input node; a LLC resonant tank circuit connected to the first input node and the second input node; a transformer winding part connected to the LLC resonant tank circuit; a rectifier circuit connected to the transformer through a first output node and a second output node; and a capacitor connected between the first input node and the first output node. The LLC resonant tank circuit can include a resonant capacitor connected to the first input node, a resonant inductor connected to the resonant capacitor, and a magnetizing inductance connected between the resonant inductor and the second input node.