Systems and methods for calculating tissue impedance in electrosurgery
An electrosurgical generator and associated methods determine a real part of the impedance of treated tissue. The electrosurgical generator includes an output stage, a plurality of sensors, and a controller that controls the output stage. The controller includes a signal processor that determines an RMS voltage, an RMS current, an average power, and a real part of the impedance of the treated tissue based on measured voltage and current by using a plurality of averaging filters. The controller controls the output stage to generate electrosurgical energy based on at least the determined real part of the impedance.
1. A method for controlling an electrosurgical generator, comprising:
generating radio frequency (RF) electrosurgical energy;
sensing a voltage waveform and a current waveform of the generated electrosurgical energy;
processing the sensed voltage waveform and the sensed current waveform using a plurality of moving averaging filters, which include first, second, and third moving average filters, to determine a Root Mean Square (RMS) voltage, an RMS current, an average power, and a real part of an impedance; and
controlling the electrosurgical energy based on at least one of the RMS current, the RMS voltage, the average power, and the real part of the impedance, wherein:
the first moving average filter outputs a mean square voltage based on the voltage waveform;
the second moving average filter outputs the average power based on the voltage waveform and the current waveform;
the third moving average filter outputs a mean square current based on the current waveform; and
the real part of the impedance is calculated by dividing the average power by the RMS current.
2. The method according to claim 1 , wherein processing the voltage waveform and the current waveform includes:
squaring, by a first multiplier, the sensed voltage waveform;
squaring, by a second multiplier, the sensed current waveform;
multiplying, by a third multiplier, the sensed voltage waveform and the sensed current waveform to obtain a power waveform;
averaging, by the first moving average filter, the squared voltage waveform to obtain the mean square voltage;
averaging, by the moving third average filter, the squared current waveform to obtain the mean square current;
averaging, by the second moving average filter, the power waveform to obtain the average power;
calculating the RMS voltage based on the average voltage waveform; and
calculating the RMS current based on the average current waveform.
3. The method according to claim 2 , wherein controlling the electrosurgical energy includes:
generating a control signal based on a difference between the real part of the impedance and a desired real part of the impedance; and
controlling the generated electrosurgical energy based on the control signal.
4. The method according to claim 1 , further comprising sampling the sensed voltage waveform and the sensed current waveform to obtain a predetermined number of samples of each of the sensed voltage waveform and the sensed current waveform.
5. The method according to claim 4 , wherein the predetermined number of samples corresponds to an integer multiple of a RF frequency of the voltage waveform and the current waveform.
6. The method according to claim 1 , wherein the moving averaging filters are selected from the group consisting of Cascaded Integrator Comb (CIC) filters, boxcar averaging filters, finite impulse response filters, infinite impulse response filters, and any combination of these averaging filters.
7. The method according to claim 1 , wherein plurality of moving averaging filters are identical to each other.
8. The method according to claim 1 , wherein the plurality of moving averaging filters are low pass filters.
9. The method according to claim 4 , further comprising synchronously operating the plurality of moving averaging filters over the same predetermined number of samples of each of the voltage waveform and the current waveform.
10. The method according to claim 1 , further comprising calculating phase information between the voltage waveform and the current waveform by dividing the average power by a product of the RMS voltage and the RMS current.