Method for controlling electrosurgical instrument capable of producing cutting plasma, and corresponding electrosurgical generator

Abstract

To provide a method for controlling an electrosurgical instrument capable of producing cutting plasma for cutting or vaporizing tissue when in operation at the tissue.SOLUTION: In the method, an electrosurgical generator generates a voltage signal being basically sinusoidal; 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 capable of providing the cutting plasma; the operating current signal includes a linear current component being sinusoidal having a fundamental frequency and a nonlinear current component not having the fundamental frequency and particularly being non-sinusoidal and / or of transient nature; and the operating current signal is controlled depending on the nonlinear current component in order to control the cutting plasma.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method of controlling an electrosurgical instrument that, during operation, is capable of generating a cutting plasma at tissue for cutting or vaporizing the tissue.The present invention also relates to an electrosurgical generator that is capable of generating a cutting plasma at tissue for cutting or vaporizing the tissue.

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

[0003] Ignition of the plasma involves two steps: first, a large current heats the saline solution around the electrode, creating a gas pocket around the electrode that is electrically insulated from the saline solution, and then a high voltage across this gas pocket causes the gas to ionize, thereby igniting the plasma. [Background technology]

[0004] Currently, the electrosurgical generators used in the TURis operate primarily with voltage control. During ignition, the output current is very large because the impedance of the conductive fluid is very low. As soon as a gas pocket forms, the current is automatically reduced as the impedance rises.

[0005] The intensity of the plasma in the known system is controlled via the output voltage. This relationship is highly non-linear, and small changes in the output voltage can cause large changes in the output power. As an example, there are three voltage settings used by the known system for different stages, and these three voltage settings can be 280V, 300V, and 320V.

[0006] In the absence of tissue contact, it would be beneficial to lower the voltage, as this would result in lower output power and fewer air bubbles obscuring the view. This is problematic in two ways. First, the minimum voltage required to maintain a stable plasma state depends on environmental settings such as temperature, electrode size, electrode position, and flow rate. Second, it is difficult to distinguish between tissue contact and no tissue contact.

[0007] A solution could be to control the current instead of the voltage. However, this mode requires short bursts of high current whenever the gas layer is about to collapse, making DC control with current limiting difficult to achieve. Thus, current limiting would significantly reduce stability as the gas layer would become unstable. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to address at least one of the above problems. In particular, a solution should be provided that allows for precise control of the cutting plasma and / or precise control of the operating current signal for supplying the cutting plasma. At least an alternative solution should be provided with respect to the solutions known so far. [Means for solving the problem]

[0009] According to the present invention there is provided a method according to claim 1. Thus, there is provided a method for controlling an electrosurgical instrument which during operation is capable of generating a cutting plasma in tissue, i.e. in the so-called working element, for cutting or vaporizing said tissue. According to this method, the electrosurgical generator generates an essentially sinusoidal voltage signal and applies the voltage signal to the electrosurgical instrument, which application results in an operating current signal capable of supplying the cutting plasma.

[0010] Thus, there is an electrosurgical generator that essentially supplies and controls the power supplied to the electrosurgical instrument. This is done so that a voltage signal is applied to the electrosurgical instrument. Such a voltage signal is essentially sinusoidal. Thus, the voltage signal is an AC signal, as a DC signal could cause harm to the patient. The lowest frequency used is 200 kHz, and thus an essentially sinusoidal voltage signal has a frequency of 200 kHz or greater.

[0011] Application of such a voltage signal to the electrosurgical instrument results in the operating current, which is therefore controlled by the voltage signal applied to cause the cutting plasma to be produced.

[0012] According to the method, the operating current signal includes a linear current component that is sinusoidal with a fundamental frequency and a non-linear current component that does not have a fundamental frequency. In particular, the non-linear current component may be non-sinusoidal and / or of a transient nature. However, it is also possible that the non-linear current component is sinusoidal and has at least a sinusoidal pattern, but does not have a fundamental frequency.

[0013] Simply put, it may be easier to control only linear and therefore sinusoidal currents. However, the current supplying the cutting plasma changes the impedance which depends on the cutting plasma, and of course on the tissue, and / or on the surrounding saline and / or gas pockets created. This was found to be mainly reflected in a nonlinear current component.

[0014] For this reason, it is proposed to control the operating current signal in response to the nonlinear current component in order to control the cutting plasma.

[0015] It has been found that processes occurring at or near tissue, and therefore in electrosurgical instruments, are strongly dependent on the nonlinear current component. While both linear and nonlinear current components are necessary to operate the cutting plasma, only or primarily the nonlinear current component is indicative of ongoing processes. Thus, in response to the nonlinear current, controls can be driven to ensure that the cutting plasma does not become too intense and break down.

[0016] The control of the operating current is in particular carried out as a feedback control, such that there is a feedback of the nonlinear current component or a signal indicative of the nonlinear current component. Based on this feedback signal, the operating current is controlled, in particular by the applied voltage signal. The feedback signal can be compared with a set value and depending on the comparison the control can be adapted accordingly. However, as one further example, different feedback control methods may be applied, such as a state controller. The set value may be changed.

[0017] According to one aspect, it is proposed to extract the linear current component from the operating current signal such that the nonlinear current component remains to receive the nonlinear current component.

[0018] A linear current component should be understood to be a sinusoidal signal. Such a sinusoidal signal, and hence a linear current component, can thus be easily described by its amplitude, frequency, and phase angle. Such a linear current component can thus be described in a simple, time-invariant manner. At least the shape of such a signal does not change very rapidly. Such a linear current component can be understood as a quasi-stationary signal. At least such a linear signal can be understood as having these parameters constant over at least one period.

[0019] Based on that, such linear current components, i.e. such sinusoidal signals described by these parameters, can therefore also be identified quite easily. One possibility is to have a specific filter. It is also possible to use a phase-locked loop (PLL) to identify at least the frequency and the phase angle. Other filters, such as Kalman filters, can be used as well.

[0020] However, as will be explained further below, any Fourier transform may be used to best advantage.

[0021] According to one embodiment, the linear current component is determined by calculating signal coefficients that characterize a first harmonic of the operating current signal, and the linear current component is described using these signal coefficients.

[0022] The signal can then be analyzed using a Fourier transform. Such a Fourier transform can generally calculate signal coefficients that characterize the first and higher harmonics of the operating current signal. In this way, the operating signal can be generally described using these Fourier signal coefficients.

[0023] The basic idea is that the first harmonic describes the linear component and the higher harmonic components describe the non-linear part of the operating current signal.

[0024] However, it is not necessary to calculate the signal coefficients of the higher harmonic components, but instead, we calculate only the signal coefficient of the first harmonic of the operating current signal, resulting in a well-defined single sinusoidal current signal.

[0025] It was also found that the frequency of the linear current component and therefore the frequency of the entire operating current signal is known. It is therefore easy to apply a Fourier transform, as such a transform requires this frequency of the signal that needs to be transformed. In this way, therefore, the signal coefficients that characterize the first harmonics of the operating current signal can be easily calculated, and therefore the linear current component can be easily identified and therefore subtracted from the entire operating current signal.

[0026] The result of the subtraction is therefore a nonlinear current component which is used to control the operating current signal and therefore in the feedback for feedback control, if feedback control is used.

[0027] According to one embodiment, the linear current component is calculated by dividing the first harmonic Fourier trigonometric coefficient a of the operating current signal according to the following formula: 1 and b 1 is determined by calculating

number

number

[0028] Thus, the first harmonic Fourier trigonometric coefficient a, which can be understood as the signal coefficient characterizing the first harmonic of the operating current signal, 1 and b 1 There is an explicit formula for calculating

[0029] Therefore, it is only necessary to sample the operating current signal and calculate these coefficients. To obtain these samples, the signal is sampled over a time interval of one period. This period or the corresponding frequency is known since the voltage signal is generated by the electrosurgical generator. It is therefore also easy to sample accurately over a time interval of almost exactly one period. Thus, the first harmonic Fourier triangular coefficient a 1 and b 1 , i.e. good and accurate results for the signal coefficients of the first harmonic can also be calculated with high quality.

[0030] However, it was also found that this calculation allows the linear current components to be calculated with a quality that is actually higher than necessary.

[0031] Therefore, such linear current components need only be used to subtract from the overall operating current signal, resulting in a remaining nonlinear current component that can be used to control the operating current signal.

[0032] According to one embodiment, the operating current signal is controlled depending on the rms value of the nonlinear current component, the rms value of the nonlinear current component being 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 obtained over one period of the linear current or voltage signal, or over several such periods, in particular over 2, 3, 4, 5 or more than 5 periods and / or over less than 10 periods. It has therefore been found that, when taking into account the expected nonlinearity, it is not necessary to take into account the instantaneous value, but rather it is sufficient to take into account the rms value. As a further consequence, it is also possible to control the operating current by supplying a sinusoidal voltage signal, but it may be sufficient to adjust the amplitude of such a sinusoidal voltage signal. In other words, it is not necessary to control the instantaneous value of this voltage signal.

[0033] Furthermore, it has been found that the nonlinear current component can be calculated based on the rms value of the linear current component and the rms value of the entire operating current signal.

[0034] In this way, control of the operating current signal is sufficient, while calculation of the nonlinear current component turns out to be extremely simple, since only the rms value of the sampled signal and the nonlinear current component defined by the Fourier coefficients above are required.

[0035] In particular, such an rms value may be sufficient even if the operating current signal is controlled depending on the nonlinear current component. It has also been found that the rms value is sufficient to take into account an operating situation of the working element, even if the nonlinear part is characteristic of that operating situation. There is no need to take into account the specific shape of the nonlinear 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 it.

[0036] The sinusoidal voltage signal is adapted in response to the nonlinear current component, in particular the amplitude of the sinusoidal voltage signal is adjusted in response to the rms value of the nonlinear current component.

[0037] According to one aspect, The rms value of the nonlinear current component I nl To control the operating current signal according to the rms value I nl is calculated using the following formula:

number

[0038] Therefore, it has been found that the linear current component can be easily taken into account by using the above first harmonic Fourier trigonometric coefficients of the operating current signal. Therefore, to calculate the nonlinear current component, only the rms value of the sampled current signal and these two coefficients are needed.

[0039] In particular, this non-linear current component may be one value per period of a linear current or voltage signal.

[0040] According to one embodiment, in order to control the operating current signal, it is proposed that the rms value of the non-linear current component is controlled to a reference value, which may also be understood as a set value.

[0041] It has been found that such a reference value of the nonlinear current component allows for a convenient and effective control, however, in order to adapt the control to the particular situation and / or in particular the dynamic behavior of the cutting plasma, the reference value may be constant according to one embodiment but may also be variable according to another embodiment with particular flexibility.

[0042] According to one embodiment, it is proposed that when the rms value of the nonlinear current component falls below a reference value or falls below a first reference value, the amplitude of the voltage signal is increased, and when the rms value of the nonlinear current component exceeds the reference value or exceeds a second reference value, the amplitude of the voltage signal is decreased.

[0043] 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 judgment can be a reference value. The basic concept is as follows.

[0044] 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 that case, the voltage signal is increased so that the nonlinear current component also increases. By increasing the amplitude of the voltage signal, a situation will be reached where the high voltage ignites the plasma. As a result, the nonlinear current component automatically increases significantly. This increase results in the nonlinear current component exceeding the reference value. Therefore, the amplitude of the voltage signal is reduced.

[0045] The nonlinear current component is further observed and used for control. If the amplitude of the voltage signal is reduced, the nonlinear current component will also be reduced. The voltage signal is controlled so that the nonlinear current component does not fall to a value that is too small, which may cause the plasma to break down. In that case, the rms value of the nonlinear current component falls below the reference value, thus generating more gas phases, and therefore the amplitude of the voltage signal will be increased again to prevent the plasma from breaking down.

[0046] Therefore, the proposed method does not allow to distinguish between the described first phase, when no plasma is yet present, and the second phase, when plasma is present. It should be noted that when the first phase changes to the second phase, i.e. when plasma is initially present, this switch from the first phase to the second phase leads to a significant increase in the nonlinear current component. This results in the nonlinear current component also exceeding the reference value. In simple terms, the nonlinear current component jumps over this reference value.

[0047] Due to this effect, it is not so important how accurate the reference value is: if the reference value is in a reasonable range, the nonlinear current components will increase beyond this reference value.

[0048] However, in order to avoid plasma breakdown and therefore to control the plasma in the second phase, the reference value can be selected such that the plasma does not break down unless the nonlinear current component falls significantly below the reference value. The reference value can therefore be selected according to what is considered to be a safe value for avoiding plasma breakdown. Such a reference value also works in the first phase, where the nonlinear current component is low and therefore below the reference value, as long as the plasma is not ignited.

[0049] Such a reference value can be determined by performing tests. Such tests can be performed by controlling the operating current in a conventional manner and observing the nonlinear current components. Such a reference value can also be determined by using a variable reference value that is adapted during such an operating process. It is also possible to perform tests in an environment similar to that which will ultimately exist when operating on real tissue. Simulations are also possible to determine suitable reference values.

[0050] However, it is also possible to use different reference values, i.e. a first reference value for controlling the first phase, i.e. for controlling the situation when the nonlinear current component falls below such a first reference value. In the second phase, a second reference value may be used, i.e. for controlling the nonlinear current component so that the plasma does not break down. When the nonlinear current component exceeds the first reference value, a switchover from the first to the second reference value can be performed. However, it is also possible to adapt a single reference value by continuously varying it.

[0051] The reference values, i.e. the first and second reference values, may each be predetermined or may be different. One possibility of how to change these reference values ​​is to change or adapt them during the control. Such control may be an adaptive control that may change the reference values ​​in response to identified changes in the environment in which the electrosurgical instrument is operating.

[0052] According to one embodiment, in a first control stage for heating the saline solution, the rms value of the nonlinear current component is controlled to a first reference value, and in a second control stage for supplying a current cutting plasma, the rms value of the nonlinear current component is controlled to a second reference value, in particular the first reference value being greater than the second reference value.

[0053] This embodiment is therefore similar to the previous embodiment, but according to this embodiment the first and second control stages are more clearly distinguished. As in the first control stage related to the first phase described above, it has been found that the first reference value must be greater than the second reference value and the voltage signal must first be increased so that the nonlinear current component also increases so that the plasma is ignited. Once the plasma is ignited, control passes to the second control stage and the nonlinear current component can be decreased again. In other words, to ignite a plasma a higher current is needed than to control an already existing plasma.

[0054] According to one aspect, an electrosurgical instrument is proposed that includes a single electrode for supplying a cutting plasma between the electrode and the saline or adjacent tissue. Thus, control of the cutting plasma depends on the interaction between the electrode and the saline or between the electrode and the adjacent tissue. However, the proposed control that depends on the nonlinear current component provides extremely fast control since the voltage signal can be adjusted each period of the linear current or voltage signal.

[0055] In other words, since the frequency of the operating current signal is 200 kHz or more, this can be the frequency of the control cycle. Any change in the interaction between the electrode and the saline or adjacent tissue will therefore result in a change in the nonlinear current component and will therefore be taken into account by the control. Therefore, the operating current signal will be adapted very quickly to compensate for any change in the interaction between the electrode and the saline or adjacent tissue.

[0056] An electrosurgical instrument may also include two electrodes that provide a cutting plasma between the two electrodes. Any change in the saline or tissue between the two electrodes will affect the plasma and therefore the operating current signal. However, it will also affect the nonlinear current components, which are also taken into account by the control as described for the single electrode.

[0057] In accordance with the present invention there is provided an electrosurgical generator for controlling an electrosurgical instrument which, in operation, is capable of generating a cutting plasma at tissue for cutting or vaporizing the tissue, the electrosurgical generator comprising: An electrosurgical generator generates a voltage signal that is essentially a sine wave, the voltage signal being applied to an electrosurgical instrument; Application of a voltage signal to the electrosurgical instrument results in an operating current signal capable of supplying a cutting plasma; The operating current signal is a linear current component that is a sine wave having a fundamental frequency; Nonlinear current components that do not have a fundamental frequency, in particular non-sinusoidal and / or transient in nature; Including, The operating current signal is controlled in response to the nonlinear current component to control the cutting plasma. The present invention is adapted to carry out a method such as

[0058] In particular, such an electrosurgical generator is adapted to carry out the method described above. The electrosurgical instrument used may be of the design described above. The electrosurgical generator may be adapted such that the method, in particular the corresponding program, is implemented in the electrosurgical generator.

[0059] According to one aspect, it is proposed that the electrosurgical generator comprises a control device adapted to control the electrosurgical generator, and that the electrosurgical generator, and in particular the control device, is adapted to perform the method according to any of the aspects described above.

[0060] Thus, there is provided a control device, which may be a processor adapted to control a frequency converter, which may be part of an electrosurgical generator and which may be capable of generating a voltage signal, in particular an essentially sinusoidal voltage signal. Hence, the method is implemented on such a processor, the processor adapted to control the frequency converter, which in turn is adapted to provide the voltage signal as an output voltage signal to an electrosurgical instrument connected to the electrosurgical generator.

[0061] According to one aspect, the electrosurgical generator includes a frequency converter connected to a control device for supplying a voltage signal, and / or an output port for connecting an electrosurgical instrument that, when controlled by the generator and during operation, can generate a cutting plasma at tissue for cutting or vaporizing the tissue, and / or a current sensor that measures the operating current and is connected to the frequency converter or control device.

[0062] The frequency converter can thus provide a voltage signal and is therefore connected to the control device, which can thus control the frequency converter and thus the voltage signal.

[0063] An electrosurgical instrument may be connected to the output port such that the voltage signal generated by the frequency converter is supplied to the connected electrosurgical instrument via the output port.

[0064] In this manner, the electrosurgical instrument is controlled by a frequency converter which is controlled by a control device.

[0065] The generator may be equipped with a current sensor for measuring the operating current. Such an operating current is provided by supplying a voltage signal to the electrosurgical instrument when it is operating in or on tissue, i.e. when it is operating with a working element. The current sensor is therefore connected to the frequency converter or the control device or both. This current sensor can therefore be used to sample the operating current, and the sampled values ​​can further be used to calculate the linear current components, in particular the first harmonic Fourier triangular coefficients based on these sampled values. On that basis, the sampled values ​​can further be used to calculate the nonlinear current components explained above.

[0066] In accordance with the present invention there is provided electrosurgical equipment comprising an electrosurgical generator according to any of the aspects described above and further comprising an electrosurgical instrument connected to the electrosurgical generator.

[0067] Such an electrosurgical instrument may therefore be of the design described above.

[0068] The invention will now be described by way of example in the accompanying drawings. [Brief description of the drawings]

[0069] [Figure 1] FIG. 1 illustrates an electrosurgical generator. [Diagram 2] FIG. 13 illustrates a simplified control structure. [Diagram 3] FIG. 2 illustrates a voltage signal and a current signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] FIG. 1 shows, merely diagrammatically, an electrosurgical generator 100 having an electrosurgical instrument 102 connected thereto and operating on tissue 104, i.e., the working element.

[0071] The electrosurgical generator 100 includes a frequency converter 106 that is controlled by a control device 108. The frequency converter 106, in operation, provides a voltage signal at its output 110 that is applied to the attached electrosurgical instrument 102, resulting in an operating current.

[0072] There is a voltage sensor 112 that measures the voltage signal and a current sensor 114 that measures the operating current. These sensors 112, 114 are connected to the control device 108 for further consideration.

[0073] The control device 108 calculates the nonlinear 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. Thus, at the frequency converter output, a voltage signal is generated which is dependent on the calculated nonlinear current component.

[0074] The voltage sensor 112 may not be necessary since it is known what voltage the frequency converter 106 will generate. It is also possible that the voltage sensor 112 is directly connected to the frequency converter 106. It is also possible that the control device 108 is part of the frequency converter 106.

[0075] FIG. 2 shows a schematic control structure 200. The control structure 200 is configured to control a nonlinear current component I nl and the reference current I ref These values ​​are subtracted in a first summing element 202 to yield a control error e. This control error e is passed to a control block 204, resulting in a voltage signal V set The set value of the voltage signal V set This set value of is fed to a frequency converter 206 which may be identical to the frequency converter 106 according to FIG.

[0076] The result of the frequency converter 206 is a voltage signal V sigThis voltage signal is passed to an electrosurgical instrument 208, which may be identical to the electrosurgical instrument 102 according to Figure 1. The electrosurgical instrument 208 also operates on tissue 210, i.e., the working element, which is shown diagrammatically.

[0077] Voltage signal V sig is applied to the electrosurgical instrument 208, an operating current i OP This operating current i OP is measured by the current sensor 214. Therefore, this operating current i OP is the sampled current sampled by the current sensor 214. This sampled current is provided to a Fourier transform block 216 and to an rms block 218. The Fourier transform block 216 calculates the first harmonic Fourier trigonometric coefficients, thus determining the linear current component I lin The rms block 218 identifies the root mean square value I rms , hence the sampling current i op In the second summing element 220, the rms value of the operating current I rms and the linear current component I lin The difference between the nonlinear current component I nl Therefore, the nonlinear current component I nl However, the nonlinear current component I nl This calculation of the current component I is just a simplified diagram of FIG. 2 which does not show all the calculation steps, and preferably nl is the rms value of the operating current I rms and the linear current component I lin That is, the second summation element 220 calculates the square root of the difference between I nl =sqrt(I rms 2 -I lin 2 ) is a simplified diagram of

[0078] However, in this way, the nonlinear current component I nl is calculated and provided to the first summation element 202 described above.

[0079] The control block 204 determines, in response to the error signal e, the reference value I ref and the nonlinear current component I nl Depending on the result of the comparison with set can be designed to increase or decrease the voltage setpoint e. The behavior may be similar to a PI control. However, preferably, it can also be realized digitally, so that in each control cycle, if the error signal e is positive, the voltage setpoint is increased by a certain increment, or when the error signal is negative, it is decreased by a certain increment, which may be the same as the described increase. This may therefore differ from the I behavior, since according to one embodiment, the amplitude of the error signal is not taken into account, but only whether it is negative or positive. However, taking into account a certain value of the error signal may also be an option.

[0080] It should be noted that the possibility of increasing the voltage setpoint by a fixed increment every control cycle results in an almost continuous behavior, since the cycle frequency can be 200 kHz or more.

[0081] Figure 3 shows the recorded voltage and current data during TURis operation. The voltage is approximately sinusoidal, while the current consists of linear and nonlinear parts corresponding to the plasma breakthrough. The nonlinear current component, which can also be understood as the "plasma current", cannot be measured directly. The idea is therefore to separate the linear current component from the nonlinear current component, i.e. from the "plasma current", and to control only the "plasma current".

[0082] One way to separate the currents 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 total measured current gives an estimate of the nonlinear current component, i.e., the "plasma current", which can be used for control. Since only the rms value of the "plasma current" is relevant, it can be calculated by subtracting it from the rms value of the total current, as well as the calculated Fourier coefficient a, according to the following equation: 1 and b 1It can be calculated from:

number

[0083] Figure 3: The solid line shows the measured voltage V during TURis operation of the electrosurgical generator. sig and current i op The data shows the current is a combination of a capacitive current that is 90° phase shifted with respect to the voltage, and a current peak in phase with the voltage. During ignition, there is a very high current in phase with the voltage. The dashed line shows the sampled current i op The first harmonic component I lin Shows.

Claims

1. 1. A method for controlling an electrosurgical instrument capable of generating, during operation, a cutting plasma at tissue for cutting or vaporizing said tissue, comprising: an electrosurgical generator generating an essentially sinusoidal voltage signal, said voltage signal being applied to said electrosurgical instrument; application of the voltage signal to the electrosurgical instrument results in an operating current signal capable of supplying the cutting plasma; The operating current signal is a linear current component that is a sine wave having a fundamental frequency; non-linear current components that do not have the fundamental frequency, in particular non-sinusoidal and / or transient in nature; Including, the operating current signal is controlled in response to the nonlinear current component to control the cutting plasma. method.

2. the linear current component is extracted from the operating current signal such that the nonlinear current component remains to receive the nonlinear current component.

2. The method according to claim 1 .

3. the linear current component is determined by calculating a signal coefficient characterizing a first harmonic of the operating current signal; The linear current components are described using these signal coefficients:

3. The method according to claim 1 or 2.

4. The linear current component is a first harmonic Fourier trigonometric function coefficient a of the operating current signal according to the following equation: １ and b １ is determined by calculating [0010] and [0025] Where: x[k] is a sample of the operating current signal; N is the number of samples used, a sample of the operational current signal is taken over a time interval of one period of the linear current signal or the voltage signal; 4. The method according to claim 1, wherein the

5. The operating current signal is controlled in response to the rms value of the nonlinear current component; 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.

5. The method according to claim 1, wherein the

6. The rms value of the nonlinear current component or the rms value I ｎｌ to control the operating current signal in response to the rms value I ｎｌ is calculated using the following formula: [0030] Where: I ｒｍｓ is the rms value of the operating current signal, a １ and b １ is the first harmonic Fourier trigonometric function coefficient of the operating current signal; 6. The method according to claim 1 , characterized in that

7. and / or the rms value of the non-linear current component or the rms value is controlled to a reference value in order to control the operating current signal; when the rms value of the nonlinear current component falls below the reference value or falls below a first reference value, the amplitude of the voltage signal is increased; and when the rms value of the nonlinear current component exceeds the reference value or exceeds a second reference value, the amplitude of the voltage signal is decreased.

7. The method according to claim 1, wherein the

8. In a first control step for heating the saline solution, the rms value of the nonlinear current component or the rms value is controlled to a first reference value or the first reference value; In a second control stage for supplying the cutting plasma, the rms value of the nonlinear current component is controlled to a second reference value; The first reference value is greater than the second reference value.

8. The method according to claim 1 , characterized in that

9. the electrosurgical instrument comprises a single electrode for delivering the cutting plasma between the electrode and saline or adjacent tissue; or the electrosurgical instrument comprises two electrodes supplying the cutting plasma between the two electrodes; 9. The method according to any one of claims 1 to 8, characterized in that

10. 1. An electrosurgical generator for controlling an electrosurgical instrument capable of generating, during operation, a cutting plasma at tissue for cutting or vaporizing said tissue, said electrosurgical generator comprising: the electrosurgical generator generating an essentially sinusoidal voltage signal, the voltage signal being applied to the electrosurgical instrument; application of the voltage signal to the electrosurgical instrument results in an operating current signal capable of supplying the cutting plasma; The operating current signal is a linear current component that is a sine wave having a fundamental frequency; Nonlinear current components that do not have a fundamental frequency, in particular non-sinusoidal and / or transient in nature; Including, The operating current signal is controlled in response to the nonlinear current component to control the cutting plasma. An electrosurgical generator adapted to carry out a method such as

11. a control device adapted to control the surgical generator; The electrosurgical generator, in particular the control device, is adapted to carry out the method according to any one of claims 1 to 9, 11. An electrosurgical generator according to claim 10.

12. a control device or a frequency converter connected to said control device for generating said voltage signal; and / or an output port for connecting an electrosurgical instrument capable of generating a cutting plasma at tissue for cutting or vaporizing said tissue when controlled by said generator and during operation; and / or a current sensor, measuring an operating current and connected to the frequency converter and / or the control device; 12. An electrosurgical generator according to claim 10 or 11, comprising:

13. 1. An electrosurgical system comprising: An electrosurgical generator according to any one of claims 10 to 12; an electrosurgical instrument connected to said electrosurgical generator; Electrosurgery equipment comprising:

Images