Electrosurgical Inverter Current Sensing for Fast Waveform Control
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Solution Overview
Problem
Electrosurgical generators face challenges in controlling high-frequency AC voltage output due to rapidly changing tissue impedance, requiring precise regulation and fast measurement to prevent overload and resonance, especially in environments with high voltages and frequencies, which existing inverters struggle to manage effectively.
Innovation Solution
A measuring sensor circuit with a capacitive coupling and series-connected shunt is used to indirectly measure current and voltage, employing a current divider with passive components to achieve fast and interference-free signal conversion, enabling precise regulation without amplifiers or buffers, and an active damping device for feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a freely oscillating single-ended generator with LC resonant circuit is used, then the structure is proven and simple, but the waveform output is difficult to control
Solution Approach 1:
The patent implements a feedback system where the actual output waveform is measured and used to adjust the inverter control, enabling precise waveform control while maintaining the simplicity of the single-ended generator structure
Solution Approach 2:
The patent replaces complex mechanical waveform control mechanisms with electronic feedback control, using measurement and signal processing to achieve waveform precision without increasing structural complexity
2Measurement precision
If class D amplifiers or multilevel inverters are used, then precise regulation and freely definable output waveforms are achieved, but power loss in power semiconductors increases at high switching frequency and voltage
Solution Approach 1:
The patent uses a measurement sensor circuit to create an electrical copy of the output signal, allowing precise regulation through feedback without requiring complex power semiconductor circuits that would generate excessive heat
Solution Approach 2:
The patent changes the measurement approach from direct power measurement to indirect voltage/proportional current measurement, enabling precise regulation while avoiding the power loss associated with high-frequency switching semiconductors
3Reliability
If an LC filter is used to isolate useful frequency from switching frequency, then frequency isolation is achieved, but undesirable resonance occurs at low load output
Solution Approach 1:
The patent introduces an intermediary measurement sensor circuit that indirectly measures output parameters through proportional relationships, avoiding the need for LC filters that cause resonance while maintaining frequency isolation through feedback control
Solution Approach 2:
The patent replaces the physical LC filter mechanism with electronic feedback control based on proportional measurement, achieving frequency isolation without the resonance problems inherent in passive filter circuits
4Speed
If direct measurement of high-frequency output is implemented, then fast measurement is achieved, but measurement complexity and interference increase in high-voltage high-frequency environment
Solution Approach 1:
The patent creates simplified electrical copies of the high-frequency output signal through capacitive coupling and proportional current measurement, enabling fast measurement without directly measuring the complex high-voltage waveform
Solution Approach 2:
The patent introduces intermediary measurement elements (capacitive coupling, shunt resistors) that translate high-voltage high-frequency signals into measurable proportional signals, reducing measurement circuit complexity while maintaining measurement speed
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 allows for accurate, low-latency measurement and control of high-frequency AC voltage output, minimizing interference and resonance risks, while reducing component complexity and cost, and enhancing system stability.
Implementation Method 1
a capacitive, preferably bipolar, coupling to a series-connected shunt as bypass with respect to the parallel capacitor
Implementation Method 2
a measuring sensor circuit having a current divider that has a capacitive, preferably bipolar, coupling to a series-connected shunt
Implementation Method 3
the shunt has a considerably lower impedance than the capacitive coupling
Data Source
AI summary
An electrosurgical generator for generating a high-frequency AC voltage for an electrosurgical instrument, having a high-voltage inverter that generates and outputs a high-frequency AC voltage. A filter having a parallel capacitor is on an output line. A measuring sensor circuit having a current divider, which has a capacitive coupling to a series-connected shunt as bypass with respect to the parallel capacitor, and having a voltage detection circuit connected to the shunt. The shunt has a considerably lower impedance than the capacitive coupling. This gives rise to a proportional ratio between the current flowing through the parallel capacitor on the output line of the electrosurgical generator and the current through the shunt. This current is converted into a voltage, which is detected. The current at the output of the inverter is determined quickly and accurately thanks to the proportional relationship. This may be used for feedback and improved monitoring and regulation.