Surgical generator with improved drive for surgical instruments

Abstract

The present application relates to a surgical generator with improved drive for a surgical instrument. The surgical generator is configured to output a high frequency alternating voltage to a surgical ultrasonic instrument. An oscillator generates a drive oscillation for an inverter which generates the high frequency voltage for the surgical instrument. A matching coil simulation device comprises a correction device acting on the drive oscillation. The correction device comprises a mixing unit and a feedback circuit which modifies the drive oscillation provided to the inverter. An estimator calculates a virtual current which would flow in a simulated matching coil if the simulated matching coil were present. Based on this and a measured output voltage, an artificial phase shift is determined for steering of the oscillator. Thereby, the transfer function is reshaped to mimic the transfer function of a physical matching coil. Thus, the cumbersome matching coil which has to be precisely tuned to the ultrasonic instrument and which limits the use of newer and different ultrasonic instruments is no longer required.

Description

TECHNICAL FIELD

[0001] The present invention relates to a surgical generator configured to output a high-frequency alternating voltage to a surgical instrument. BACKGROUND

[0002] In surgical procedures, surgical instruments such as ultrasonic instruments are employed in all fields of surgical procedures for cutting tissue and sealing blood vessels, even larger blood vessels. The advantage of such surgical procedures is that a minimal heat spread is generated, thereby minimizing adverse effects on adjacent tissue. Depending on the actual task at hand, various different ultrasonic instruments are used.

[0003] Surgical ultrasonic instruments comprise an ultrasonic transducer which converts the electrical energy provided by the surgical generator into ultrasonic energy which can then be used for therapy. Generally, the ultrasonic instrument is a complex load for the surgical generator. The electrical impedance is complex and depends on the frequency and, furthermore, undergoes significant resonances corresponding to mechanical resonance modes. The mechanical resonances themselves are influenced by the mechanical load actually present at the surgical instrument, which in turn depends on the kind of tissue being treated and can thus change quite dynamically during the application of the surgical instrument.

[0004] For the driving of ultrasonic instruments, the surgical generator needs an inverter or amplifier, e.g. a class-D amplifier, with an adjustable frequency. In order to adapt the output of the amplifier to the actually used ultrasonic instrument, a matching circuit is needed. The matching circuit usually consists of a parallel inductor, called matching coil, which is connected in parallel to the surgical instrument and serves to shape the impedance characteristics of the instrument such that the desired mechanical resonance mode can be excited. In Figure 6 An exemplary implementation of such a configuration is shown in. The matching coil serves two purposes usually. First, it improves the transfer function of the surgical generator, i.e. the output voltage acting on the instrument is a function of the input signal used to drive the amplifier. Second, the matching coil improves the phase measurement needed by a phase-locked loop circuit (PLL) which is usually used to follow the resonance frequency when it changes in use due to changes in the mechanical load to the instrument.

[0005] However, the matching coil is rather bulky, dedicated to the instrument and thus rather expensive. Furthermore, being dedicated to the instrument means that the matching coil has to be tuned to the specific transfer characteristics of the ultrasonic instrument. Thus, only those ultrasonic instruments are connectable which were already available at the time the surgical generator and its matching coil were developed. In other words, the surgical generator is associated with the instruments already existing at the time of its manufacture. This is a serious limitation which limits the use of newer, more advanced ultrasonic instruments.

[0006] US 10265117 B2 has proposed a different concept by alternatively converting to a static capacitance of a surgical ultrasound instrument, abolishing the concept of tuning to a resonance frequency, thereby avoiding the task of providing a matching coil. However, this requires a continuous repeated measurement of the static capacitance. SUMMARY

[0007] It is therefore an object of the present invention to provide an improved surgical generator which provides a better adaptation to the actually used ultrasound instrument.

[0008] In a surgical generator configured to output a high-frequency alternating voltage to a surgical instrument, the surgical generator comprising a main control unit, an oscillator generating a drive oscillation, and an inverter generating the high-frequency alternating voltage from the drive oscillation, the high-frequency alternating voltage being provided via a filter and a matching circuit to an output socket for connecting the surgical instrument, wherein the matching circuit is provided for matching the power output of the inverter to the surgical instrument, according to the invention the matching circuit is formed by a matching coil simulation device configured to simulate a matching coil, the matching coil simulation device comprising: (i) a correction device acting on the drive oscillation, the correction device comprising a mixing unit and a feedback circuit, an input of the feedback circuit being connected to the output socket, wherein the feedback circuit calculates a correction signal provided as input to the mixing unit, a further input of the mixing unit receiving the drive oscillation, an output of the mixing unit being provided to the inverter; and (ii) an artificial phase generator configured to provide an artificial phase signal input to the oscillator, the artificial phase generator comprising an estimator for determining a virtual current of the simulated matching coil, and being configured to determine a phase shift between the virtual current and a measured output voltage, the artificial phase as output of the artificial phase generator being different from the phase shift between the measured output voltage and current.

[0009] The present invention aims at providing a specific matching circuit, thereby replacing the physical matching coil. The present invention recognizes that it needs a combination of two different features in order to provide such a matching circuit which is able to replace the physical matching coil. First, the oscillation used by the inverter generating the output voltage has to be modified by the correction device in dependence on the state of the actual electrical parameters (e.g. voltage and current) at the output socket. The mixing unit alters the signal emitted by the oscillator in dependence on the output of the feedback circuit, e.g. subtracting (or adding) the time-varying output value of the feedback circuit from the time-varying drive oscillation, thereby providing a modified oscillation for driving the inverter. For this purpose, the mixing unit is preferably configured to provide a real-time mixing (e.g. by subtraction or addition) of time-varying signals. The core aspect is that by means of the feedback circuit and the mixing unit, it is possible to realize a shaping of the transfer function of the amplifier and the filter between the amplifier and the output, thereby employing the filter to imitate the effect of the matching coil. By this, it is possible to make use of the filter which is needed anyway, to make the matching coil superfluous.

[0010] However, this cannot work alone. Therefore, as a second key aspect, the signal needed for the correction device needs to be generated. With a physically matching coil, the actual load experienced by the surgical instrument in combination with the physically matching coil will form a complex impedance that results in a certain phase difference of the current to the output voltage. However, in the absence of a physically matching coil, this phase difference cannot be measured, as it also depends on the current through the absent matching coil. Therefore, the present invention provides an artificial phase generator that uses the measured actual voltage and a virtual current that combines the actual output with the imaginary current through the (absent) matching coil. For this, an estimator is provided that is configured to determine the virtual current that would flow as output current if a matching coil would be present. By the combination of these elements, the current that would be present if a correctly sized matching coil would be present can be determined, and from this the virtual current is calculated.

[0011] Therefore, the missing current signal can be provided for determining the phase shift between the current considering a correctly sized but absent matching coil and the actually measured voltage; and a signal for this phase shift can be used to correctly drive the calibration device to implement the transfer function of the analog (absent) matching coil. As a result, due to the reshaped transfer function by means of the correction device, the same voltage and current with the same phase shift will be received by the ultrasound instrument as if the regular, bulky and expensive matching coil would be present. Due to this electronic analog, this analog is flexible and can also correctly work for newly developed surgical ultrasound instruments with different electrical characteristics, unlike the matching coil that has to be always tuned to a specific surgical ultrasound instrument and its electrical characteristics.

[0012] Therefore, the present invention achieves a significant improvement in different key aspects, namely, more versatility in the ultrasound instruments to be used, and further reduction of the volume and cost of the surgical generator itself, while increasing the flexibility in the ultrasound instruments that can be used, even newer ultrasound instruments.

[0013] In the context of the present application, the term "high frequency" relates to frequencies in the range of the ultrasound frequencies generated by the surgical generator, typically in the range of 20 kHz to 200 kHz (ultrasound surgical generator).

[0014] The inverter is the device that provides the actual high frequency output for the surgical ultrasound instrument to be connected to the output socket. The term inverter is quite broad and includes actual inverter technology as well as transformers and amplifiers.

[0015] The filter is located between the output of the inverter and the output socket, thereby separating the load from the output of the inverter. Typically, the filter comprises an inductance in line and can also comprise a parallel capacitor (LC filter).

[0016] The matching coil simulation device is configured to simulate a matching coil that existed in the past to match the instrument to the surgical generator. As a simulation device, the matching coil simulation device does not comprise a matching coil itself; it can thus be said to be coil-less.

[0017] In the context of the present invention, an estimator is understood to be a device that aims to estimate the state of a system from measurements of the output of the system. It is configured to estimate a variable or state that cannot or at least cannot be directly estimated by using parameters of the output of the system and other measured variables. Various such estimators are known to the person skilled in the art of control systems. Non-limiting examples can be observers in state space or Wiener and Kalman filters.

[0018] In a preferred embodiment, the feedback circuit is configured as state feedback. Thereby, the benefits obtained in control engineering by implementing state space can be used in an advantageous manner.

[0019] Preferably, the feedback circuit can be configured to be provided with a signal representing the measured output voltage and / or current as input to the feedback circuit. Measuring the output voltage and / or current can be realized in a reliable manner with minimal effort, in particular, considering that sensors for voltage and current are anyway provided at the output in order to facilitate power regulation by the main control unit. Thus, by using the measured output voltage (or current) signal, which is anyway measured, for the feedback circuit, no additional costs in terms of sensors are involved.

[0020] Advantageously, the feedback circuit is configured as a negative feedback, which comprises a preselectable amplification factor that can be applied at the input of the feedback circuit. Such an amplification factor (which can also be referred to as k-factor) can be used to implement a feedback circuit that is not complex and efficient. Preferably, the amplification factor is determined depending on a ratio of the filter inductance to an inductance value of the matching coil that is matched to the surgical instrument. This inductance value is the inductance that the physical matching coil (which is to be simulated by the present invention) would have in order to be matched to the surgical instrument. Furthermore, preferably, the ratio is also modified by a ratio of the current flowing through the inductance in the line of the filter to the current that is expected to flow through the physical matching coil (if present). By taking this ratio, any influence of the transformer in the output line is also taken into account.

[0021] Advantageously, the feedback circuit, in particular its amplification factor, is set automatically depending on the type of the surgical instrument. Thereby, the user is relieved from the task of determining the amplification factor. However, this does not exclude a manual interaction for setting the amplification factor, for example, by the user manually selecting the type of the instrument and thereby setting the amplification factor, for example, by means of a look-up table.

[0022] Preferably, the feedback circuit is configured to output a wave signal having the same frequency as the drive oscillation but a different amplitude and / or phase than said drive oscillation. With such a configuration, the wave signal can be used quite directly for the correction device without the need for pre-processing. This further simplifies the correction device and its operation.

[0023] In a preferred embodiment, the oscillator comprises a frequency following circuit configured to follow the frequency of the voltage at the output socket. In view of such following, the oscillator tracks any changes in the resonant frequency experienced at the output socket due to a changing load, in particular a changing mechanical load of a surgical ultrasound instrument connected at the output socket. Preferably, the frequency following circuit comprises a phase-locked loop circuit (PLL). This allows for an efficient and reliable tracking of the frequency at the output socket. Safe and stable operating conditions can thereby be achieved.

[0024] Further, preferably, the frequency following circuit is controlled by a phase signal generated by an artificial phase generator. This enables the frequency following circuit to track the frequency and the phase shift at the output socket even if a direct measurement of the phase is not possible. This also solves the case where the actually measured phase does not represent the phase information required for a correct operation of the correction device. This is particularly useful if the phase information about the phase shift is artificially generated, e.g. by employing an estimator for the amplitude and the phase of an electric current which is not directly measurable (e.g. a virtual current).

[0025] Advantageously, the estimator for the virtual current comprises a parameter representing the inductance of the matching coil to be emulated. By employing such a parameter, a more precise estimation of the virtual current which would flow as output current if the matching coil was present and connected in parallel to the surgical instrument can be achieved. The parameter is preferably set in dependence of the type of surgical ultrasound instrument connected to the output socket. This can be done manually or automatically. Preferably, the main control unit is configured to set this parameter. This includes that the main control unit is configured to determine the type of surgical instrument by means of a user input device and / or to determine the type of surgical instrument automatically, e.g. by reading out instrument data of the surgical ultrasound instrument. Thereby, an efficient and easy to use way for setting the inductance parameter is achieved which eliminates any risk of user errors in case of an automatic determination by the main control unit. This further enhances reliability and finally improves the safety of the patient. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A surgical generator with an electric surgical instrument attached is shown according to an exemplary embodiment;

[0027] Figure 2 A surgical generator with an electric surgical instrument attached is shown according to an exemplary embodiment; Figure 1a block diagram of a surgical generator as shown;

[0028] Figure 3a , Figure 3b is a transmission function showing the gain and phase of the system for no matching coil, physical matching coil and simulated matching coil according to the invention;

[0029] Figure 4a , Figure 4b is the instrument output impedance for no matching coil, physical matching coil and simulated matching coil according to the invention;

[0030] Figure 5 is the drive oscillation without modification by the correction device and after modification by the correction device; and

[0031] Figure 6 a block diagram of a power section from an inverter to an ultrasonic instrument connected at an output socket according to the prior art is shown. DETAILED DESCRIPTION

[0032] The invention is explained by means of an exemplary embodiment of a surgical generator according to the invention. This exemplary embodiment is a surgical ultrasonic generator as a whole identified by reference numeral 1. The surgical ultrasonic generator 1 comprises a housing 11 provided with a general user interface 14, a power selector knob 12 and an instrument type selector knob 13 and an output socket 15 for a surgical ultrasonic instrument 16. The surgical ultrasonic instrument 16 is connected via a cable to the output socket 15 of the surgical ultrasonic generator 1.

[0033] The surgical ultrasonic generator 1 is powered by a mains cable 21 which can be connected at its end by means of a plug 20 to a public power grid (not shown) or other suitable power source. Thereby, electrical power is provided to the surgical ultrasonic generator 1.

[0034] A schematic functional diagram of the electrosurgical generator 1 is exemplarily illustrated in Figure 2 . It comprises in the housing 11 a power supply unit 22 which is provided with electrical power by means of the mains connection cable 21 (see Figure 1 ). The power supply unit 22 comprises a rectifier and feeds a direct voltage to a DC link 23 which feeds an inverter 24. In the exemplary embodiment, the inverter 24 is an amplifier, preferably of the class D type. Based on a high frequency drive oscillation 43 provided by a drive oscillator 3, the inverter 24 amplifies the provided high frequency oscillation and generates a corresponding high frequency alternating voltage of about 10 to 100 volts, typically about 50 volts. The high frequency is variable and in the ultrasonic range between 20 kHz and 60 kHz, typically in the range between 40 kHz and 55 kHz.

[0035] The high frequency voltage generated by the inverter 24 is fed to the output lines 25. Following the inverter 24, a filter 26 is provided, which is an LC type filter having an in-line inductance 26* in either of the lines of the output lines 25 and a capacitor connecting the two in-line inductances. Following the filter 26 and an optional DC blocking capacitor 28, an isolation transformer 29 is arranged, which provides isolation and step-up of the output voltage, the output transformer having a transmission ratio of e.g. 11. The resulting output voltage and current are sensed by current measuring means 17 and voltage measuring means 18 and are delivered to the output socket 15 into which a surgical ultrasound instrument 16 can be plugged. The configuration from the inverter 24 to the output socket 15 forms the power section of the surgical ultrasound generator 1.

[0036] The operation of the surgical ultrasound generator 1 is controlled by the main control unit 10. It is connected to the power supply unit 22 and the inverter 24 by means of signaling lines. Furthermore, a power feedback circuit 19 is provided to which the current measuring means 17 and the voltage measuring means 18 are connected as inputs. The power feedback circuit 19 determines the output power based on these inputs and outputs a signal representing the actual output power to the main control unit 10, which in turn provides control signals to the inverter 24 according to the function and mode set by the user through the user interface 14 and / or the power selection knob 12. It also controls the initial frequency f of the driving oscillator 3. This configuration described so far is well known in the art and will not be further explained for the sake of brevity.

[0037] The surgical ultrasound instrument 16 comprises an ultrasound transducer (not shown) which converts electrical energy into ultrasound energy. The electrical impedance of the surgical ultrasound instrument 16 corresponds to a mechanical resonance mode of the surgical ultrasound instrument 16. This mechanical resonance is influenced by the mechanical load on the ultrasound instrument, which is variable, e.g. depending on the tissue the ultrasound instrument is to work on.

[0038] By way of reference, the power section starting with an amplifier serving as inverter 104 according to the prior art is shown in Figure 6 Following the LC filter 106, the DC blocking capacitor 108, the isolation transformer 109, the current and voltage measuring means 117 and 118 and the matching coil 9 and finally the output socket into which the surgical ultrasound instrument 16 is to be plugged. In order to drive the surgical ultrasound instrument 16 correctly, it is necessary to have the output voltage and current of the matching coil 9 to be known. This is achieved by the current and voltage measuring means 117 and 118, which are connected to the power feedback circuit 19. Figure 6The matching circuit, which consists of a parallel inductor identified by reference 9. The matching coil 9 is used to shape the impedance characteristics of the surgical ultrasound instrument 16 so that the desired mechanical resonance mode can be excited. The matching coil 9, which is usually part of the surgical ultrasound generator, must therefore be matched to the actual surgical ultrasound instrument 16. If another surgical ultrasound instrument 16 should be connected to the ultrasound surgical generator, a second matching coil is required, or the matching coil 9 must be a switchable matching coil that can be reconfigured to match the other surgical ultrasound instrument.

[0039] The present application aims to eliminate the matching coil 9. The matching coil 9 is therefore not present in the exemplary embodiment shown in the figures, and in particular, in the Figure 2 In the present case, the eliminated matching coil 9 is shown in dashed lines. According to the present application, the eliminated matching coil 9 is replaced by a matching coil simulation device which is configured to simulate the eliminated matching coil 9. To this end, the matching coil simulation device comprises a correction device 4 which is configured to perform a correction to the drive oscillation formed by the oscillator 3 and an artificial phase generator 6 which comprises an estimator 61 for determining a virtual current of the simulated matching coil.

[0040] The estimator 61 is configured to determine the virtual current as the output current, and on the basis thereof, the artificial phase generator 6 calculates the phase shift between the virtual current and the measured output voltage. To this end, the actual voltage measured by the voltage sensor 18 is provided to a first input 62 of the estimator 61. Furthermore, the actual current measured by the current sensor 17 is provided to a second input 63 of the estimator 61. In addition, as an additional input, there is provided a parameter 60 which represents the inductance value "L" of the non-existent matching coil. On the basis thereof, the estimator 61 is configured to determine the (complex) virtual current I virt. :

[0041]

[0042] where I meas. is the current measured by the current sensor 17 and U meas. is the voltage measured by the voltage sensor 18. The value of the virtual current I virt. is provided at the output 64 and to an input 67 of a phase shift calculator 65, and the measured voltage signal measured by the voltage sensor 18 is provided to a further input 66 of the phase shift calculator 65. On the basis of these inputs there, the phase shift calculator 65 determines the phase shift between the voltage and the current, i.e. the measured voltage U meas. and the virtual current I virt. . The signal for this phase shift is output from the artificial phase generator 6 at a line 68. The signal for the artificial phase difference This signal is provided to the input of the PLL 33 of the oscillator 3 for frequency following.

[0043] It is worth noting that this phase shift calculated by the artificial phase generator 6 is and must be different from the actual phase shift defined by the actual voltage and current measured by the current sensor 17 and the voltage sensor 18, due to the additional consideration of the imaginary current of the matching coil by simulation.

[0044] In the depicted embodiment, the oscillator 3 comprises a basic generating unit 30 generating a sinusoidal oscillation. The frequency of the generated oscillation is determined by a frequency following circuit 32, to which an initial frequency f is provided by the main control unit 10 as a control signal. Based on this initial frequency, the oscillator 3 emits a drive oscillation at its output, which is provided via the correction device 4 to the inverter 24 acting as an amplifier. The frequency following circuit 32 further comprises a phase-locked loop (PLL) circuit 33. It receives the phase difference In view thereof, the PLL circuit 33 keeps the oscillator 3 at a constant phase shift between the measured output voltage and current, and further, the oscillator 3 tracks any changes in the resonance frequency as they occur over the course of using the surgical ultrasound instrument 16 due to varying load conditions.

[0045] Furthermore, the transfer function of the power section starting from the inverter 24 acting as an amplifier is shaped by using the correction device 4. For this purpose, a feedback circuit 5 is provided having an input 50 to which the voltage signal V meas. measured by the voltage sensor 18 is provided. In addition, as an additional input 51, the parameter "k" is provided at the feedback circuit 5.

[0046] The "k" parameter can be determined by the inverse of the inductance L that the matching coil 9 would have (if it were present) multiplied by the line inductance 26* (since such a line inductance 26* exists in both lines, it is doubled in this case). Furthermore, taking into account the isolation transformer 29, the ratio between the current in the line in filter inductance 26* and the current flowing through the matching coil 9 (if it is present) can be determined, and in the present case, the ratio is N = 11. Assuming an inductance L of the matching coil 9 of 3.3 mH and a line in inductance 26* of 6.25 μH each, the "k" parameter can be determined as:

[0047]

[0048] Based on this, the feedback circuit 5 determines the signal at the output 52 as a function of -k · V meas. to determine a correction value at the output 52 of the feedback circuit 5. This is provided to the second input 42 of the mixing unit 40 of the correction device 4. At the first input 43 of the mixing unit 40, the drive oscillation output by the oscillator 3 is provided. Thus, the drive oscillation output by the oscillator 3 is corrected by the output of the feedback circuit 5, and the resulting signal is provided via the line 44 to the input of the inverter 24 for amplification and output to the output line 25.

[0049] As a result, therefore, the transfer function is shaped by the correction device 4, and the phase shift between voltage and current at the output socket 15 is modified by the artificial phase generator 6. The resulting corrected oscillation provided by the line 44 differs in amplitude and phase from the original drive oscillation output by the oscillator 3. This is shown in Figure 5 , where the dashed line represents the original drive oscillation, and the solid line represents the corrected oscillation shaped according to the present application and provided via the line 44 to the inverter 24 for amplification.

[0050] The effect of the correction device 4 and the artificial phase generator 6 is shown in Figure 3a , Figure 3b and Figure 4a , Figure 4b . Figure 3a The gain depending on the frequency f at the output socket 15 is shown, and Figure 3b the phase shift depending on the frequency f at the output socket 15. The dashed line shows the transfer function of the power section according to the prior art, in which the physical matching coil 9 is present. By removing the matching coil only, the transfer function would be as shown by the dotted line, which differs significantly in terms of gain and even more so in terms of phase. By providing the matching coil simulation device comprising the correction device 4 and the artificial phase generator 6 as described before, the transfer function would be as shown by the solid line. It can be easily recognized that the solid line closely tracks and overlaps to a large extent the dashed line of the physical matching coil.

[0051] Similarly, in Figure 4a and Figure 4b , the amplitude and phase of the output impedance of the surgical ultrasound instrument 16 are shown. The output impedance according to the prior art, in which the physical matching coil 9 is present, is shown by the dashed line. The scenario of removing the matching coil 9 only is plotted by the dotted line. It can be easily recognized that this line is completely different and, in particular, provides a significant deviation in phase, resulting in a second root at frequencies above the resonance frequency of 47 kHz, which is detrimental to stability. By providing the output impedance according to the present application, resulting in the output impedance as shown by the solid line, in particular, near the critical resonance frequency around 47 kHz, more closely approaching the dashed line of the physical matching coil, these problems are solved. Thus, it can be easily recognized that the matching coil simulation device produces superior results in replacing the physical matching coil 9.

[0052] Thus, in view of the combination of the correction device 4 and the artificial phase generator 6, the desired effect of emulating (physically non-existing) matching coils 9 in order to correctly drive the surgical ultrasound instrument 16 is achieved.

[0053] Furthermore, in order to be able to correctly drive other types of surgical ultrasound instruments 16 which require different emulated matching coils 9, the parameter "L" can be pre-selected to different values by means of the main control unit 10 via the line 69. The type of surgical ultrasound instrument 16 used can be selected by the user by means of the rotary knob 13 attached to the main control unit 10. Alternatively, the main control unit can be arranged to read out the type directly from the surgical ultrasound instrument 16 by means of a communication interface (not shown) at the output socket 15. In any case, thus, it is achieved that the surgical ultrasound generator 1 is easily adaptable to different types of surgical ultrasound instruments 16, even if such instruments are released after the ultrasound surgical generator has already been manufactured. This greatly improves the versatility.

[0054] Furthermore, the present application is described above by way of example with surgical ultrasound instruments and surgical ultrasound generators, but the present application is not limited thereto. Other systems in which the generator outputs a high-frequency electrical signal which is matched to the instrument can be readily thought of by the skilled person, and the present application can be applied thereto as well.

Claims

1. A surgical generator configured to output a high-frequency alternating voltage to a surgical instrument (16), the surgical generator comprising a main control unit (10), an oscillator (3) generating a drive oscillation, and an inverter (24) generating a high-frequency alternating voltage from the drive oscillation, the high-frequency alternating voltage being supplied via a filter and a matching circuit to an output socket (15) for connecting the surgical instrument (16), wherein, A matching circuit is provided to match the power output of the inverter (24) with the surgical instrument (16). Its features are, The matching circuit is formed by a matching coil simulation device configured to simulate a matching coil, the matching coil simulation device comprising: A correction device (4) is applied to the drive oscillation. The correction device (4) includes a mixing unit (40) and a feedback circuit (5). The input (50) of the feedback circuit (5) is connected to the output socket (15). The feedback circuit (5) calculates a correction signal provided as input (42) to the mixing unit (40). Another input (43) of the mixing unit (40) receives the drive oscillation. The output (44) of the mixing unit (40) is provided to the inverter (24). An artificial phase generator (6) is configured to provide an artificial phase signal as an input to the oscillator (3). The artificial phase generator includes an estimator (61) for determining a virtual current of a simulated matching coil and is configured to determine the phase shift between the virtual current and the measured output voltage. The artificial phase output of the artificial phase generator (6) is different from the phase shift between the measured output voltage and the current.

2. The surgical generator of claim 1, wherein, The feedback circuit (5) is configured for status feedback.

3. The surgical generator of either of Claims 1 or 2, wherein, A signal representing the measured output voltage and / or output current is provided at the input (50) to the feedback circuit (5).

4. The surgical generator according to claim 1 or 2, characterized in that, The feedback circuit (5) is configured as negative feedback and includes a pre-selectable amplification factor.

5. The surgical generator according to claim 4, characterized in that, The amplification factor is determined based on the ratio of the filter inductance (26*) to the inductance of the matching coil (9) matched to the surgical instrument (16).

6. The surgical generator according to claim 1, 2, or 5, characterized in that, The feedback circuit (5) is automatically configured according to the type of the surgical instrument (16).

7. The surgical generator according to claim 1, 2, or 5, characterized in that, The mixing unit (40) is configured to output a wave signal having the same frequency as the driving oscillation but a different amplitude and / or phase.

8. The surgical generator according to claim 1, 2, or 5, characterized in that, The oscillator (3) includes a frequency follower circuit (32) configured to follow the frequency of the voltage at the output socket (15).

9. The surgical generator according to claim 8, characterized in that, The frequency follower circuit (32) includes a phase-locked loop circuit (33).

10. The surgical generator according to claim 8, characterized in that, The frequency follower circuit (32) is controlled by the artificial phase signal generated by the artificial phase generator (6).

11. The surgical generator according to claim 1, 2, 5, 9 or 10, characterized in that, The estimator (61) for the virtual current includes a parameter representing the inductance L of the matching coil (9) to be simulated.

12. The surgical generator according to claim 11, characterized in that, This indicates that the parameters of the inductor L can be selected in advance.

13. The surgical generator according to claim 11, characterized in that, The main control unit (10) is configured to set the parameters representing the inductance according to the type of the surgical instrument (16) connected to the output port (15).

14. The surgical generator according to claim 1, 2, 5, 9, 10, 12 or 13, characterized in that, The main control unit (10) is configured to determine the type of the surgical instrument (16) by means of a user input device (13) and / or automatically by reading the instrument data of the surgical instrument (16).

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