Method for controlling electrosurgical instrument, electrosurgical generator and electrosurgical apparatus

Abstract

The invention relates to a method for controlling an electrosurgical instrument, an electrosurgical generator and an electrosurgical apparatus. The invention relates to an electrosurgical instrument capable of generating a cutting plasma for cutting or vaporizing a tissue when operating at the tissue, in which an electrosurgical generator generates a substantially sinusoidal voltage signal and the voltage signal is applied to the electrosurgical instrument, the application of the voltage signal to the electrosurgical instrument results in an operating current signal, the operating current signal is capable of providing the cutting plasma, and the operating current signal comprises a linear current component having a fundamental frequency and being sinusoidal and a non-linear current component not having a fundamental frequency, the non-linear current component being particularly non-sinusoidal and / or having transient properties, wherein the operating current signal is controlled in accordance with the non-linear current component in order to control the cutting plasma.

Description

Technical Field

[0001] The present invention relates to a method for controlling an electrosurgical instrument capable of generating a cutting plasma for cutting or vaporizing tissue when operating at the tissue. The present invention also relates to an electrosurgical generator capable of generating a cutting plasma for cutting or vaporizing tissue. Background Art

[0002] The present invention relates to the generation of cutting plasma during the TURIS (Transurethral Resection in Saline) procedure. During this procedure, prostate and bladder tissue can be cut / vaporized with a plasma ignited around an electrode inserted into a so-called working element.

[0003] Ignition of the plasma involves two steps. First, a saline solution surrounding an electrode is heated with a high electric current. This creates a gas pocket around the electrode, electrically isolating it from the salt water. Then, a high voltage across this gas pocket causes the ionization of the gas, thus igniting the plasma.

[0004] Currently, electrosurgical generators for TURIS are mainly operated by voltage control. During ignition, the output current is very high because the impedance of the conductive fluid is very low. Once the air pocket is formed, the current automatically decreases as the impedance rises.

[0005] The intensity of the plasma in the known system is controlled via the output voltage. The relationship is strongly nonlinear, and a small change in the output voltage can significantly change the output power. As an example, for different phases, the known system can use three voltage settings, and these three voltage settings can be 280V, 300V and 320V.

[0006] When there is no tissue contact, reducing the voltage would be beneficial as this results in lower output power and fewer bubbles obstructing the line of sight. This is challenging in two ways. First, the minimum voltage required to maintain stable plasma conditions depends on environmental settings such as temperature, electrode size, electrode position, flow rate, etc. Second, it is difficult to distinguish between tissue contact and non-tissue contact.

[0007] A solution could be to control not the voltage but the current. However, DC control involving current limiting is not feasible because the mode requires a short high current surge every time the gas layer is about to collapse. Therefore, setting a current limit will significantly reduce stability because the gas layer will become unstable.

[0008] The object of the present invention is therefore to solve at least one of the above problems. In particular, a solution should be provided which enables a more precise control of the cutting plasma and / or a more precise control of the operating current signal for providing the cutting plasma. At least one alternative solution to the solutions known to date should be provided. Summary of the invention

[0009] According to the invention, a method for controlling an electrosurgical instrument is provided, which, when operating at tissue (i.e. in a so-called working element), is capable of generating a cutting plasma for cutting or vaporizing tissue. According to the method, an electrosurgical generator generates a substantially sinusoidal voltage signal and applies the voltage signal to the electrosurgical instrument, wherein applying the voltage signal to the electrosurgical instrument results in an operating current signal, which is capable of providing the cutting plasma.

[0010] Therefore, there is an electrosurgical generator that basically provides and controls the power supplied to the electrosurgical instrument. This is done so that a voltage signal is applied to the electrosurgical instrument. This voltage signal is essentially sinusoidal. Therefore, the voltage signal is an alternating signal, because a DC signal may harm the patient. The lowest frequency to be used is 200kHz, and therefore the essentially sinusoidal voltage signal has a frequency of 200kHz or higher.

[0011] Applying this voltage signal to the electrosurgical instrument results in the operating current. Therefore, the operating current is controlled by means of the applied voltage signal, thereby generating cutting plasma.

[0012] According to the method, the operating current signal comprises a linear current component which is sinusoidal and has a fundamental frequency and a nonlinear current component which does not have a fundamental frequency. In particular, the nonlinear current component may be non-sinusoidal and / or may have transient properties. However, the nonlinear current component may also be sinusoidal, at least have a sinusoidal part, but not have a fundamental frequency.

[0013] In simple terms, it may be easier to control only a linear and therefore sinusoidal current. However, the current provided to the cutting plasma changes the impedance, which depends on the cutting plasma. This of course also depends on the tissue or the surrounding saline and / or the air pockets created. It has been found that this is mainly reflected in the nonlinear current component.

[0014] Based on this understanding, it is proposed to control the operating current signal according to the non-linear current component in order to control the cutting plasma.

[0015] It has been found that the process being performed at or near the tissue and therefore at the electrosurgical instrument is largely dependent on the nonlinear current component. Both the linear current component and the nonlinear current component are needed to operate the cutting plasma, but only the nonlinear current component or mainly the nonlinear current component is indicative of the process being performed. Therefore, depending on the nonlinear current, the control device can be driven so that the cutting plasma neither becomes too strong nor breaks down.

[0016] The control of the operating current is particularly performed as a feedback control, so that there is a feedback of the non-linear current component or a signal indicating the non-linear current component. Based on the feedback signal, the operating current is controlled, in particular by an applied voltage signal. The feedback signal can be compared with a set value, and according to the comparison, the control can be adjusted accordingly. However, different feedback control methods can be applied, such as a state controller, to give only one further example. The set value can also vary.

[0017] According to one aspect, it is proposed that in order to receive the non-linear current component, the linear current component is subtracted from the operating current signal such that the non-linear current component remains.

[0018] A linear current component is to be understood as a sinusoidal signal. Thus, such a sinusoidal signal and thus a linear current component can be easily described by its amplitude, frequency and phase angle. Thus, such a linear current component can be described in a simple and time-invariant manner. At least the shape of such a signal does not change too fast. Such a linear current component can be understood as a quasi-stationary signal. At least such a linear signal can be understood such that these parameters are constant for at least one cycle.

[0019] Based on this, such a linear current component, i.e. such a sinusoidal signal described by these parameters, can therefore also be easily identified. One possibility is to use a specific filter. A phase-locked loop (PLL) can also be used at least for identifying the frequency and phase angle. Other filters, such as a Kalman filter, can also be used.

[0020] However, as will be explained further below, the most advantageous Fourier transform may be used.

[0021] According to one aspect, the linear current component is determined by calculating signal coefficients characterizing the first harmonic of the operating current signal, and these signal coefficients are used to describe the linear current component.

[0022] Therefore, the signal can be analyzed using Fourier transform. Such Fourier transform can generally calculate the signal coefficients that characterize the first harmonic and higher harmonics of the operating current signal. In this way, these Fourier signal coefficients can be used to describe the operating signal as a whole.

[0023] The basic idea is that the first harmonic describes the linear component, while higher harmonic components will describe the nonlinear part of the operating current signal.

[0024] However, it is not necessary to calculate the signal coefficients of the higher harmonic components, but only the signal coefficients of the first harmonic of the operating current signal. The result is a clear single sinusoidal current signal.

[0025] It is also found that the frequency of the linear current component and therefore the frequency of the overall operating current signal is well known. Therefore, it is easy to apply the Fourier transform, since such a transform requires the frequency of the signal to be transformed. Therefore, in this way, the signal coefficients characterizing the first harmonic of the operating current signal can be easily calculated, and therefore the linear current component can be easily identified and therefore subtracted from the overall operating current signal.

[0026] Therefore, the result of the subtraction is a nonlinear current component, and this is used to control the operating current signal. Therefore, if such feedback control is used, this feedback is used for feedback control.

[0027] According to one aspect, the linear current component is determined by calculating the first harmonic Fourier triangular coefficients a1 and b1 of the operating current signal according to the following formula:

[0028]

[0029] and

[0030]

[0031] in

[0032] x[k] is a sample of the operating current signal, and

[0033] N is the number of samples used, and

[0034] Samples of the operating current signal are acquired at time intervals of one cycle of the linear current signal or voltage signal.

[0035] In this way, therefore, there is a clear formula for calculating the first harmonic Fourier triangular coefficients a1 and b1 , which can be understood as signal coefficients characterizing the first harmonic of the operating current signal.

[0036] Therefore, all that is required is to sample the operating current signal and calculate these coefficients. To obtain these samples, the signal is sampled at a time interval of one cycle. This period or the corresponding frequency is well known, because the voltage signal is generated by the electrosurgical generator. Therefore, it is also easy to accurately sample at an almost exact time interval of one cycle. Therefore, good and accurate results for the first harmonic Fourier trigonometric coefficients a1 and b1, i.e. the signal coefficients of the first harmonic, can also be calculated with high quality.

[0037] However, it has also been found that, through this calculation, the linear current component can be calculated with substantially higher quality than is necessary.

[0038] Therefore, this linear current component can only be used to be subtracted from the overall operating current signal, thereby obtaining a remaining non-linear current component, which can then be used to control the operating current signal.

[0039] According to one aspect, the operating current signal is controlled as a function of the rms value of the non-linear current component and the rms value of the non-linear current component is calculated by calculating the square root of the difference between the square of the rms value of the operating current signal and the square of the rms value of the linear current component. Such rms value is in particular taken within one period or a plurality of such periods of the linear current signal or voltage signal, in particular within 2, 3, 4, 5 or more than 5 periods and / or less than 10 periods. It has therefore been found that even taking into account the expected non-linearity, it is not necessary to take into account the instantaneous value, but that the rms value is sufficient. As a further consequence, the operating current can also be controlled by providing a sinusoidal voltage signal, while it is sufficient to adjust only the amplitude of this sinusoidal voltage signal. In other words, it is not necessary to control the instantaneous value of the voltage signal.

[0040] It has further been found that it is sufficient to calculate the non-linear current component based on the rms value of the linear current component and the rms value of the overall operating current signal.

[0041] It has been found that in this way, control of the operating current signal is sufficient, while the calculation of the non-linear current component is very simple, since all that is required is the rms value of the sampled signal and the non-linear current component defined by the Fourier coefficients.

[0042] In particular, such an rms value may be sufficient even if the operating current signal is controlled in dependence on a non-linear current component. It has also been found that even if the non-linear part is characteristic of an operating situation in the working element, the rms value is sufficient to take into account the operating situation. It is not necessary to take into account a specific shape of the non-linear current component. It has also been found that the energy used is an important characteristic of the situation and therefore the rms value is a good value to describe the situation.

[0043] The sinusoidal voltage signal is adjusted according to the nonlinear current component. In particular, the amplitude of the sinusoidal voltage signal is adjusted according to the rms value of the nonlinear current component.

[0044] According to one aspect, it is recommended that:

[0045] In order to calculate the rms value of the nonlinear current component I nl or the rms value Inl To control the operating current signal, use the following formula to calculate the rms value I nl :

[0046]

[0047] in

[0048] I rms is the rms value of the operating current signal, and

[0049] a1 and b1 are the first harmonic Fourier trigonometric coefficients of the operating current signal.

[0050] It is thus found that by using the first harmonic Fourier triangular coefficients of the operating current signal, the linear current component can be easily taken into account. Thus, only the rms value of the sampled current signal and these two coefficients are required to calculate the non-linear current component.

[0051] In particular, the non-linear current component may be one value per period of the linear current signal or voltage signal.

[0052] According to one aspect, it is suggested that in order to control the operating current signal, the rms value of the nonlinear current component is controlled as a reference value. The reference value can be understood as a set value.

[0053] It has been found that with this reference value for the nonlinear current component, a simple and effective control is possible. However, in order to adapt the control to the specific situation and / or in particular the dynamic behavior of the cutting plasma, the reference value can be constant according to one aspect, but can also be variable according to another aspect which is particularly more flexible.

[0054] According to one aspect, it is suggested that the amplitude of the voltage signal increases when the rms value of the nonlinear current component is lower than a reference value or lower than a first reference value, and the amplitude of the voltage signal decreases when the rms value of the nonlinear current component is higher than a reference value or higher than a second reference value.

[0055] Therefore, the voltage signal can be increased to increase the nonlinear current component, and the voltage signal can be decreased to decrease the nonlinear current component. The standard can be a reference value. The basic concept is as follows.

[0056] It has been found that the nonlinear current component corresponds to the intensity or amplitude of the plasma. As long as there is no gas phase, the nonlinear current component is small. Therefore, in this case, the voltage signal is increased in order to also increase the nonlinear current component. By increasing the amplitude of the voltage signal, a situation will be reached when a high voltage will cause the plasma to ignite. Therefore, the nonlinear current component will automatically increase significantly. This increase will cause the nonlinear current component to exceed a reference value. Therefore, the amplitude of the voltage signal will decrease.

[0057] The nonlinear current component will be further observed and used for control. When the amplitude of the voltage signal decreases, the nonlinear current component will also decrease. The voltage signal will be controlled so that the nonlinear current component does not drop to too small a value, because at too small a value, the plasma may break down. In this case, the rms value of the nonlinear current component will be lower than the reference value, and therefore the amplitude of the voltage signal will be increased again in order to generate more gas phase, thereby preventing the breakdown of the plasma.

[0058] Thus, by the proposed method, it is possible not to distinguish between the above-mentioned first stage when there is no plasma and the second stage when there is plasma. It should be noted that once the first stage becomes the second stage, i.e., when the plasma is present for the first time, this switch from the first stage to the second stage will result in a significant increase of the nonlinear current component. This will also result in the nonlinear current component exceeding the reference value. In short, the nonlinear current component will jump over the reference value.

[0059] For this effect, it is not so important which exact value the reference value has. If the reference value is within a reasonable range, the non-linear current component will increase above the reference value.

[0060] However, in order to avoid breakdown of the plasma, and therefore in order to control the plasma in the second stage, the reference value can be selected so that the plasma does not break down as long as the non-linear current component does not drop significantly below the reference value. Therefore, the reference value can be selected according to the above-mentioned value, which is considered to be a safe value for avoiding plasma breakdown. As long as there is no plasma ignition, this reference value will also work for the first stage, in which the non-linear current component is low and therefore below the reference value.

[0061] Such reference values ​​can be found by conducting tests. Such tests can be done by controlling the operating current in a conventional manner and observing the nonlinear current component. The above reference values ​​can also be found by using a variable reference value that is applicable during such an operating process. It is also possible to conduct tests in an environment similar to the environment that will eventually exist when operating on real tissue. Simulations can also find sufficient reference values.

[0062] However, it is also possible to use different reference values, i.e. a first reference value for controlling the first stage, i.e. for controlling the nonlinear current component below the first reference value. For the second stage, a second reference value can be used, i.e. controlling the nonlinear current component so that the plasma does not break down. As soon as the nonlinear current component exceeds the first reference value, a switch from the first reference value to the second reference value can be made. However, it is also possible to adjust the single reference value by continuously changing the single reference value.

[0063] The reference value or the first reference value and the second reference value may each be predetermined or may vary. One possibility of how to vary these reference values ​​is to vary or adapt these reference values ​​during control. Such control may be an adaptive control which may vary the reference values ​​according to identified changes in the environment in which the electrosurgical instrument is operating.

[0064] According to one aspect, it is suggested that in a first control stage for heating brine, the rms value of the nonlinear current component is controlled to a first reference value or said first reference value, and in a second control stage for providing current cutting plasma, the rms value of the nonlinear current component is controlled to a second reference value, wherein in particular, the first reference value is greater than the second reference value.

[0065] Thus, this aspect is similar to the previous aspect, and according to this aspect, the first control stage and the second control stage are more clearly identified. It has been found that the first reference value should be greater than the second reference value, as in the first control stage, which relates to the first stage described above, the voltage signal first needs to increase so that the nonlinear current component also increases so that the plasma is ignited. Once the plasma is ignited, control is transferred to the second control stage, and the nonlinear current component can be reduced again. In other words, in order to ignite the plasma, a higher current is required than to control the already existing plasma.

[0066] According to one aspect, the proposed electrosurgical instrument comprises a single electrode for providing a cutting plasma between the electrode and saline or adjacent tissue. Thus, the control of the cutting plasma depends on the interaction between the electrode and the saline or between the electrode and adjacent tissue. However, the proposed control depending on the non-linear current component provides very fast control, since the voltage signal can be adjusted at each cycle of the linear current signal or voltage signal.

[0067] In other words, since the frequency of the operating current signal is 200 kHz or higher, it can also be the frequency of the control cycle. Therefore, any changes in the interaction between the electrode and the saline or adjacent tissue will result in changes in the non-linear current component and will therefore be taken into account by the control. Therefore, the operating current signal will be adapted to compensate for any changes in the interaction between the electrode and the saline or adjacent tissue fairly quickly.

[0068] It is also possible that the electrosurgical instrument comprises two electrodes to provide the cutting plasma between the two electrodes. Any changes in the saline or tissue between the two electrodes will have an effect on the plasma and therefore on the operating current signal. However, it will also affect the non-linear current component and will also be taken into account by the control as described for a single electrode.

[0069] According to the present invention, there is also provided an electrosurgical generator for controlling an electrosurgical instrument, which, when operating at tissue, is capable of generating cutting plasma for cutting or vaporizing tissue, wherein the electrosurgical generator is adapted to perform the following method, according to which:

[0070] - an electrosurgical generator generates a substantially sinusoidal voltage signal, and the voltage signal is applied to an electrosurgical instrument, wherein

[0071] - applying a voltage signal to the electrosurgical instrument to obtain an operating current signal, the operating current signal being capable of providing a cutting plasma, and

[0072] -Operation current signals include:

[0073] a linear current component that has a fundamental frequency and is sinusoidal, and

[0074] A non-linear current component having no fundamental frequency and, in particular, being non-sinusoidal and / or having a transient nature, wherein

[0075] - controlling the operating current signal based on the non-linear current component to control the cutting plasma.

[0076] In particular, such an electrosurgical generator is suitable for carrying out the method as described above. The electrosurgical instrument used can be designed as described above. The electrosurgical generator can be suitable for carrying out the method, in particular the corresponding procedure, on the electrosurgical generator.

[0077] According to one aspect, it is proposed that an electrosurgical generator comprises a control device adapted to control the electrosurgical generator, wherein the electrosurgical generator and in particular the control device are adapted to perform a method according to any of the above-mentioned aspects.

[0078] Therefore, a control device is provided, which may be a processor adapted to control a frequency converter. The frequency converter may be part of an electrosurgical generator and is capable of generating a voltage signal, in particular a substantially sinusoidal voltage signal. Therefore, the method may be implemented on the processor, and the processor is adapted to control the frequency converter, and the frequency converter is adapted to provide the voltage signal as an output voltage signal to an electrosurgical instrument connected to the electrosurgical generator.

[0079] According to one aspect, the electrosurgical generator includes a frequency converter for providing a voltage signal, which is coupled to a control device and / or includes an output port for connecting an electrosurgical instrument, which is capable of generating a cutting plasma for cutting or vaporizing tissue when controlled by the generator and operated at tissue, and / or the frequency converter includes a current sensor for measuring the operating current and is coupled to the frequency converter or the control device.

[0080] The frequency converter can thus provide the voltage signal and the frequency converter is thus coupled to the control device. The control device can thus control the frequency converter and thereby the voltage signal.

[0081] An electrosurgical instrument can be coupled to the output port and in this way the voltage signal generated by the frequency converter is provided to the connected electrosurgical instrument via the output port.

[0082] In this way, the electrosurgical instrument is controlled by a frequency converter which is controlled by the control device.

[0083] The generator may comprise a current sensor for measuring an operating current. This operating current is the result of providing a voltage signal to the electrosurgical instrument when operating in or at the tissue, i.e. when operating at the working element. The current sensor is thus coupled to the frequency converter or the control device or to both. Thus, the current sensor can be used to sample the operating current, and the sampled values ​​can further be used to calculate linear current components, in particular first harmonic Fourier trigonometric coefficients, based on these sampled values. Based on this, the sampled values ​​can further be used to calculate nonlinear current components, as described above.

[0084] According to the present invention, there is provided an electrosurgical apparatus comprising an electrosurgical generator according to any one of the above aspects and an electrosurgical instrument connected to the electrosurgical generator.

[0085] Therefore, the electrosurgical instrument can be designed as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The present invention will now be described by way of examples based on the accompanying drawings.

[0087] Figure 1 An electrosurgical generator is shown.

[0088] Figure 2 A simplified control structure is shown.

[0089] Figure 3 The voltage and current signals are shown. DETAILED DESCRIPTION

[0090] Figure 1 An electrosurgical generator 100 is shown to which an electrosurgical instrument 102 is connected, operating on tissue 104 (ie, a working element), shown schematically only.

[0091] The electrosurgical generator 100 includes a frequency converter 106 that is controlled by a control device 108. When operating, the frequency converter 106 provides a voltage signal at its output 110 that is applied to an attached electrosurgical instrument 102, thereby generating an operating current.

[0092] There is a voltage sensor 112 for measuring a voltage signal and a current sensor 114 for measuring an operating current. For further considerations, these sensors 112, 114 are connected to the control device 108.

[0093] The control device 108 calculates the non-linear current component from the current sample values ​​provided by the current sensor 114. Based on this, the control device 108 controls the frequency converter 106. Therefore, at the frequency converter output, a voltage signal is generated according to the calculated non-linear current component.

[0094] The voltage sensor 112 may not be necessary, since it is known what voltage the frequency converter 106 produces. The voltage sensor 112 may also be connected directly to the frequency converter 106. The control device 108 may also be part of the frequency converter 106.

[0095] Figure 2 A schematic control structure 200 is shown. The control structure 200 shows that the control is based on the nonlinear current component I nl and reference current I ref These values ​​are subtracted in the first summing element 202 to obtain the control error e. The control error e is passed to the control block 204, thereby generating the set value V of the voltage signal set The voltage signal is set to V set is given to the frequency converter 206, which can be connected with the frequency converter according to Figure 1 The same as the frequency converter 106.

[0096] The result of the frequency converter 206 is a voltage signal V sig The voltage signal is transmitted to the electrosurgical instrument 208, which can be used in accordance with Figure 1 The electrosurgical instrument 208 is the same as the electrosurgical instrument 102. The electrosurgical instrument 208 also operates on the schematically shown tissue 210, ie, operates on a working element.

[0097] The voltage signal V sig Applied to the electrosurgical instrument 208, the operating current i OP The operating current i is measured by the current sensor 214. OP Therefore, the operating current i OP is the sampled current sampled by the current sensor 214. The sampled current is provided to the Fourier transform block 216 and the rms block 218. The Fourier transform block 216 calculates the first harmonic Fourier trigonometric coefficients and identifies the linear current component I in this way. lin rms block 218 calculates the root mean square value I rms , so that the sampling current i OP In the second summing element 220, the rms value of the operating current I is calculated. rmsWith the linear current component I lin The difference between the nonlinear current component I nl Therefore, the nonlinear current component I nl is also an rms value. However, the nonlinear current component I nl This calculation is just Figure 2 The simplified diagram in FIG. 1 does not show all the calculation steps, and preferably, the current component I nl By taking the current I rms The square of the rms value and the linear current component I lin The second summing element 220 is I nl =sqrt(I rms 2 -I lin 2 ) is a simplified diagram of the

[0098] However, in this way, the nonlinear current component I nl is calculated and provided to the first summing element 202 as described above.

[0099] The control block 204 can be designed so that, depending on the error signal e, the reference value I ref With the nonlinear current component I nl The comparison result sets the voltage setting value V set Increase or decrease. This behavior may be similar to a PI control. However, preferably, this may also be implemented digitally so that in each control cycle, if the error signal e is positive, the voltage setpoint may be increased by a certain increment, or, when the error signal is negative, it may be decreased by a specific increment, which may be the same as the increase described. Thus, this may differ from the I behavior, since according to one aspect, the amplitude of the error signal may not be considered, but only whether it is negative or positive. However, considering a specific value of the error signal may also be an option.

[0100] It should be noted that the possibility to increase the voltage setpoint by a constant increment every control cycle will result in an almost continuous behavior since the cycle frequency can be 200 kHz or higher.

[0101] Figure 3 Voltage and current data recorded during TURis operation are shown. The voltage is approximately sinusoidal, while the current consists of a linear part and a nonlinear part corresponding to plasma breakdown. The nonlinear current component can also be denoted as "plasma current" and cannot be measured directly. Therefore, the idea is to separate the linear current component from the nonlinear current component, i.e. from the "plasma current", and control only the "plasma current".

[0102] One way to separate the current is to use a Fourier transform to calculate the first harmonic of the measured current. This includes any capacitive and ohmic currents. Subtracting this measured current from the overall measured current gives an estimate of the nonlinear current component, the "plasma current", which can then be used for control. Since only the rms value of the "plasma current" is relevant, it can be calculated from the rms value of the total current and the calculated Fourier coefficients a1 and b1 according to the following formula:

[0103]

[0104] Figure 3 : The solid line shows the voltage V measured during TURis operation of the electrosurgical generator sig and current i OP The current is a combination of a capacitive curve that is 90° phase-shifted relative to the voltage and a current peak that is in phase with the voltage. During ignition, there is a very high current that is in phase with the voltage. The dashed line shows the sampled current i OP The first harmonic component I lin .

Claims

1. A method for controlling an electrosurgical instrument capable of generating a cutting plasma for cutting or vaporizing tissue when the electrosurgical instrument is operated at the tissue, wherein: An electrosurgical generator generates a substantially sinusoidal voltage signal, and the voltage signal is applied to the electrosurgical instrument, applying the voltage signal to the electrosurgical instrument to obtain an operating current signal, the operating current signal being capable of providing the cutting plasma, and The operating current signal includes: a linear current component that has a fundamental frequency and is sinusoidal, and Non-linear current components without fundamental frequency, in particular non-sinusoidal and / or of transient nature, wherein The operating current signal is controlled based on the non-linear current component to control the cutting plasma.

2. The method according to claim 1, wherein: To receive the non-linear current component, the linear current component is subtracted from the operating current signal such that the non-linear current component remains.

3. The method according to claim 1 or 2, wherein: The linear current component is determined by calculating a signal coefficient characterizing a first harmonic of the operating current signal, and These signal coefficients are used to describe the linear current component.

4. A method according to any one of the preceding claims, wherein: The linear current component is determined by calculating the first harmonic Fourier triangular coefficients a1 and b1 of the operating current signal according to the following formula: and in, x[k] is a sample of the operating current signal, and N is the number of samples used, and where A sample of the operating current signal is acquired within a time interval of one cycle of the operating current signal or the voltage signal.

5. A method according to any one of the preceding claims, wherein: controlling the operating current signal according to the rms value of the nonlinear current component, and The rms value of the nonlinear current component is calculated by calculating a square root of a difference between a square of an rms value of the operating current signal and a square of an rms value of the linear current component.

6. A method according to any one of the preceding claims, wherein: In order to calculate the rms value of the nonlinear current component I nl or the rms value I nl To control the operating current signal, the following formula is used to calculate the rms value I nl : in, I rms is the rms value of the operating current signal, and a1 and b1 are the first harmonic Fourier trigonometric coefficients of the operating current signal.

7. A method according to any one of the preceding claims, wherein: In order to control the operating current signal, the rms value of the nonlinear current component or the rms value is controlled to be a reference value, and / or When the rms value of the nonlinear current component is lower than the reference value or lower than the first reference value, the amplitude of the voltage signal increases, and When the rms value of the nonlinear current component is higher than the reference value or higher than a second reference value, the amplitude of the voltage signal decreases.

8. A method according to any one of the preceding claims, wherein: In a first control stage for heating brine, the rms value of the nonlinear current component or the rms value is controlled to a first reference value or the first reference value, and In a second control stage for providing the cutting plasma, the rms value of the nonlinear current component is controlled to be a second reference value, wherein, The first reference value is greater than the second reference value.

9. A method according to any one of the preceding claims, wherein: The electrosurgical instrument comprises a single electrode for providing the cutting plasma between the electrode and saline or between the electrode and adjacent tissue, or The electrosurgical instrument includes two electrodes to provide the cutting plasma between the two electrodes.

10. An electrosurgical generator for controlling an electrosurgical instrument capable of generating a cutting plasma for cutting or vaporizing tissue when the electrosurgical instrument is operated at the tissue, wherein: The electrosurgical generator is suitable for performing the following method, according to which: The electrosurgical generator generates a substantially sinusoidal voltage signal, and the voltage signal is applied to the electrosurgical instrument, wherein applying the voltage signal to the electrosurgical instrument to obtain an operating current signal, the operating current signal being capable of providing the cutting plasma, and The operating current signal includes: a linear current component that has a fundamental frequency and is sinusoidal, and Non-linear current components without fundamental frequency, in particular non-sinusoidal and / or of transient nature, wherein The operating current signal is controlled based on the non-linear current component to control the cutting plasma.

11. The electrosurgical generator of claim 10, comprising: A control device adapted to control the electrosurgical generator, wherein: The electrosurgical generator, in particular the control device, is adapted to perform a method according to any one of claims 1 to 9.

12. The electrosurgical generator according to claim 10 or 11, comprising: a frequency converter for generating the voltage signal, the frequency converter being coupled to the control device or coupled to the control device, and / or an output port for connecting an electrosurgical instrument capable of generating a cutting plasma for cutting or vaporizing the tissue when controlled by the electrosurgical generator and operating at the tissue, and / or A current sensor is used to measure the operating current and is coupled to the frequency converter and / or the control device.

13. An electrosurgical device, comprising: An electrosurgical generator according to any one of claims 10 to 12, and An electrosurgical instrument is connected to the electrosurgical generator.

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