Common Mode Choke for Electrosurgical Resonant Inverter EMC
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Solution Overview
Problem
Existing electrosurgical generators using phase-shifted full bridge resonant inverters face challenges with electromagnetic compatibility (EMC) due to common mode currents generated by FET transitions, leading to increased complexity and cost.
Innovation Solution
Incorporating a common mode choke with a ferrite core and adjustable leakage inductance to impede common mode currents while allowing differential currents to pass, reducing the number of components and improving performance by using an LCLC tank topology and H-bridge configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase-shifted full bridge resonant inverter is used to generate electrosurgical energy, then the electrosurgical procedure can be performed, but common mode currents are generated causing electromagnetic compatibility problems
Solution Approach 1:
A common mode choke is introduced as an intermediary component between the H-bridge and the load. The choke's common mode windings present high impedance to common mode currents generated by FET transitions, effectively blocking these harmful currents while allowing differential mode signal transmission. This mediator resolves the electromagnetic compatibility issue without altering the fundamental resonant inverter operation.
Solution Approach 2:
The leakage inductance of the common mode choke, which initially appears as a parasitic effect, is utilized beneficially as the series inductance component (Ls) of the resonant circuit. By properly designing the choke's winding structure and spacing, the harmful common mode current generation is converted into a useful resonant inductance that enables the electrosurgical generator operation.
2Reliability
If common mode currents are blocked to improve electromagnetic compatibility, then EMC problems are reduced, but the complexity and cost of the generator increase
Solution Approach 1:
The common mode choke is designed to perform multiple functions simultaneously: (1) blocking common mode currents to improve EMC, (2) providing the series inductance Ls for the resonant circuit operation, and (3) enabling adjustable leakage inductance through movable core halves. By making the choke multi-functional, additional EMC protection components are eliminated, reducing overall system complexity despite adding the choke itself.
3Reliability
If the leakage inductance of the choke is increased to improve common mode current blocking, then EMC performance improves, but the ability to pass differential currents may be affected
Solution Approach 1:
The choke incorporates movable core halves that allow dynamic adjustment of the magnetic coupling between primary and secondary windings. By changing the spacing between core halves, the leakage inductance can be adjusted: larger spacing increases leakage inductance for better common mode blocking, while smaller spacing reduces leakage inductance to improve differential current transmission. This dynamic adjustability resolves the contradiction between the two opposing requirements.
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 impedes common mode currents, reducing electromagnetic compatibility issues and simplifying the generator design, thereby enhancing performance and reducing costs.
Implementation Method 1
The resonant inverter includes a common mode choke that impedes common mode currents
Implementation Method 2
Incorporating a common mode choke with a ferrite core
Data Source
AI summary
The present disclosure is directed to an electrosurgical generator including a tank configured to output energy and an H-bridge configured to drive the tank. The generator also includes a choke. The choke impedes a common mode current generated by the H-bridge and provides a leakage inductance for the tank.