Electrosurgical generator with dual output

Abstract

An electrosurgical generator for outputting a high-frequency alternating voltage to electrosurgical instruments, comprising a first / second RF generating unit (4, 4') that supplies a first / second high-frequency alternating voltage with a first / second frequency to a first / second output (16, 16'), configured for connecting a first / second electrosurgical instrument (19, 19'). Upon activation, a first current flows through the first electrosurgical instrument and simultaneously a second current flows through the second electrosurgical instrument. The actual operating currents (Iw1, Iw2) delivered by the electrosurgical instruments to the tissue being treated are important for proper and safe operation but cannot be measured directly. The invention provides an observer unit (6) configured for the indirect determination of the first and second operating currents (Iw1, Iw2) based on measured values.The observer unit, designed to indirectly determine the operating currents, can use these as input signals for an inverter control (3) which is designed to receive calculated operating currents, thereby achieving improved control of the electrosurgical generator.

Description

[0001] The invention relates to an electrosurgical generator designed to output a high-frequency alternating voltage to electrosurgical instruments. The electrosurgical generator comprises a generating unit that produces high-frequency (HF) alternating voltages, which are supplied to at least two output sockets designed for the simultaneous connection and activation of electrosurgical instruments.

[0002] In electrosurgery, also known as radiofrequency surgery, an electrosurgical instrument, such as an electrosurgical scalpel, is used to apply high-frequency alternating current to tissue in the human body. Typically, radio frequencies in the range of approximately 200 kHz to 4,000 kHz are used. This results in localized heating of the tissue. The tissue is then cut or severed by heating and removed through thermal resection. A major advantage is that bleeding can be stopped simultaneously with the incision by occluding the affected vessels, and that electrosurgical instruments can also be used for other applications, such as coagulation. Different applications require different electrosurgical instruments.

[0003] In some applications, it may be necessary to perform surgical procedures with more than one, especially two, electrosurgical instruments simultaneously (dual activation). To enable this, separate electrosurgical generators can be used, one for each instrument. A typical problem is that interference can occur between the outputs of the high voltages generated by the generators. This interference can include an undesirable low-frequency oscillation, similar to the phenomenon that occurs in acoustics when two frequencies are close to each other but not exactly the same. Furthermore, cross-currents are generated within the body, flowing from one electrosurgical instrument to another.Such cross-currents impede the proper control of the currents / power delivered to the two electrosurgical instruments, thus compromising operational safety. A further costly complication is the need to provide two electrosurgical generators.

[0004] A similar situation arises when a single electrosurgical generator with two inverters and power stages is used, allowing for dual activation of the electrosurgical instruments. However, avoiding unwanted interference remains challenging. This can be mitigated by using a single inverter that alternately powers the two outputs. However, this limits its use to modulated modes with a duty cycle of less than 50%, which is a significant limitation.

[0005] Furthermore, it had been suggested to perform a power measurement for both outputs. However, this has the disadvantage that it is only possible for outputs with the same settings and the same mode. Moreover, the actual power distribution between these two outputs is unknown.

[0006] Another approach involves supplying the two outputs with voltages having two different fundamental frequencies and performing a discrete Fourier transform (DFT) on the measurements at both outputs using a Goertzel-type filter (EP 3 912 580 A1). If the fundamental frequencies are not perfectly orthogonal, overlaps occur between them, resulting in discontinuities in a Goertzel array diagram. This is used to determine whether a significant transverse conductance is present. If a certain threshold is exceeded, the RF generation and output are shut down as a safety measure. Alternatively, based on this approach, a beat frequency amplitude can be measured to determine a measure of the impedance.However, this at best allows for an estimation of the cross-current and not a precise determination of the operating current actually delivered into the treated tissue by the respective electrosurgical instrument connected to one of the outputs. Although this is a feasible safety device, the control of the energy delivered by the respective electrosurgical instrument still needs improvement.

[0007] It is therefore an object of the invention to provide an improved electrosurgical generator with two outputs that reduces this disadvantage.

[0008] The solution according to the invention lies in the features of the independent claim. Advantageous embodiments are the subject of the dependent claims.

[0009] An electrosurgical generator configured to output a high-frequency alternating voltage to electrosurgical instruments, comprising a first RF generating unit that supplies a first high-frequency alternating voltage with a first frequency to a first output, a second RF generating unit that supplies a second high-frequency alternating voltage with a second frequency different from the first frequency to a second output, wherein the first and second outputs are configured to connect a first and a second electrosurgical instrument such that, in an activated state, a first current flows through the first electrosurgical instrument and simultaneously a second current flows through the second electrosurgical instrument, and a central control unit configured to control the operation of the electrosurgical generator, including the simultaneous operation of the first and second RF generating units.According to the invention, the inverter control is configured such that it receives calculated operating currents as an input signal, wherein the operating currents are obtained by an operating current calculation device which is communicatively connected to the inverter control, wherein the operating current calculation device comprises an observer unit which is configured for an indirect determination of the first and the second operating current based on measured values ​​obtained by a dual measurement of the actual output currents at the first and the second output.

[0010] The following are some terms used in connection with the invention: In the field of electrosurgical generators, the term "high frequency" refers to frequencies that are typically in the range between 200 kHz and 4000 kHz and are also known as radio frequency (RF).

[0011] The term "high voltage" generally refers to voltages up to 10 kV, preferably up to 4000 V, preferably at least 10 V.

[0012] Within the scope of the present invention, an observer unit is understood to be a device that serves to determine the state of a system from measurements of its outputs. It is configured to determine a variable or a state that is not, or at least not directly, accessible by using parameters and other measured quantities output by the system. Various such observers are known to those skilled in the art of control systems.

[0013] The inverter unit is a device that provides the actual high-frequency alternating voltage for the surgical instrument to be connected to the output socket. This term is quite broad and encompasses inverter technology as well as converters and amplifiers.

[0014] A cross current is a portion of the total current delivered by one output that flows to the other output when the RF generator is activated. A working current is the other portion of the total current, with this working current actually flowing from the output through the electrosurgical electrode to the tissue being treated (and back to the same output in the case of a bipolar configuration, or to a separate neutral electrode in the case of a monopolar configuration). The working current and the cross current together constitute the (total) current of each output. These (total) currents are measured by sensors located at the outputs and / or the output leads.

[0015] The underlying problem is that the operating current actually delivered by the electrosurgical instruments to the tissue being treated cannot be measured directly. This is primarily due to the presence of a cross-current between the two outputs.

[0016] The invention recognizes that improved control of the outputs and the electrosurgical instruments they supply can be achieved by using the operating current (or the resulting power) as a control signal, even though the operating current cannot be directly measured. Although this may seem paradoxical at first glance, the invention recognizes that the difficulties encountered with known concepts can be overcome in this way.

[0017] The core of the invention is to use an operating current that is not measured but calculated – since direct measurement is not possible – and to create an observer unit designed for the indirect determination of the operating current based on measured values, in particular the directly measurable (total) output current of both outputs. These operating currents determined in this way for both outputs are then used as input signals for the inverter control.

[0018] The invention takes advantage of the fact that, due to the first and second RF generation units, a voltage with a first frequency is present at the first output and a voltage with a second frequency is present at the second output, resulting in a beat frequency and a cross-current. However, as soon as a cross-current occurs, the measured current at either output is a combination of the currents from both frequencies. Within the scope of the invention, it was recognized that this allows not only the detection of the presence of cross-currents, but also that the dual-frequency characteristic can be used to determine the current component supplied by the output, which is the actual operating current.

[0019] The invention thus enables the direct determination of the individual operating currents for both outputs. This allows for significantly improved control of the energy delivered by the respective electrosurgical instruments. Furthermore, the uncertainties inherent in prior art methods involving mere estimation can be effectively avoided. The quality of the control can be increased, the operational reliability of the electrosurgical generator enhanced, and the risks to the patient resulting from undetected or misjudged overcurrents and / or crosscurrents effectively reduced.Preferably, the observer unit comprises a Fourier series approximation device and an automatic coefficient determination device, wherein the Fourier series approximation device is configured to actually calculate an approximation by dual Fourier series, one for the first operating current and one for the second operating current, and the automatic coefficient determination device is configured to calculate coefficients of the dual Fourier series approximation based on the measured values ​​of the dual output currents and transmit the coefficients to the Fourier series approximation device. As is known to those skilled in the art, the quality of the approximation can be determined by choosing the order in which the Fourier series is to be formed. Higher orders provide more accurate results, but this is often unnecessary. In a preferred embodiment, the first-order approximation, i.e.,With regard to the fundamental frequency, an optimum between sufficiently accurate results and the required computational effort / required computing power.

[0020] The automatic coefficient determination is first explained using a simplified Fourier series, which represents a first-order approximation (fundamental frequency). It uses K measured samples of the measurable (total) current of the first output I1 to determine an offset coefficient for a Fourier series around the first frequency f1. a1,0(k)=2K∑k−KkI1(k) as well as two first-order coefficients: a1,1(k)=2K∑k−KkI1(k)⋅cos(2⋅π⋅f1⋅k⋅Δ) b1,1(k)=2K∑k−KkI1(k)⋅cos(2⋅π⋅f1⋅k⋅Δ) with a Δ as the sampling time.

[0021] Similarly, an offset coefficient is determined based on the measurable (total) current of the second output I2. a2,0(k)=2K∑k−KkI2(k) as well as for the two first-order coefficients: a2,1(k)=2K∑k−KkI2(k)⋅cos(2⋅π⋅f1⋅k⋅Δ) b2,1(k)=2K∑k−KkI2(k)⋅cos(2⋅π⋅f1⋅k⋅Δ)

[0022] The same process is performed for a second Fourier series around the second frequency f2, resulting in a set of six additional coefficients. These coefficients, determined by the automatic coefficient determination unit, are then forwarded to the Fourier series approximation unit of the observer unit.

[0023] In a system with two monopolar electrosurgical instruments, the determination of the actual working currents flowing through the electrosurgical instrument connected to the first output is called current I. w1 , as well as through the electrosurgical instrument connected to the second output, current I w2 , realized in the observer unit as shown below by way of example, where I(k) denotes a single measured value: Iw1(k)=a1,0,f1+a2,0,f12+(a1,1,f1+a2,1,f1)⋅cos(2⋅π⋅f1⋅k⋅Δ)+(b1,1,f1+b2,1,f1)⋅sin(2⋅π⋅f1⋅k⋅Δ) Iw2(k)=a1,0,f2+a2,0,f22+(a1,1,f2+a2,1,f2)⋅cos(2⋅π⋅f2⋅k⋅Δ)+(b2,1,f2+b2,1,f2)⋅sin(2⋅π⋅f2⋅k⋅Δ)

[0024] The crossflow I cross can be easily determined by subtracting the respective measured total current I1 (or I2) from the operating current I. w1 (or I w2 ) is subtracted according to Kirchhoff's current law. The corresponding voltage is V. cross .

[0025] The respective resistances R of the impedances Z are calculated accordingly, where cos(φ u,i ) - abbreviated cos(φ) - denotes a power factor that is determined by a phase shift φ between voltage and current: Rw1=Zw1cos(φu,i)=V1,rmsIw1,rms⋅cos(φu,i) Rw2=Zw2cos(φu,i)=V2,rmsIw2,rms⋅cos(φu,i) Rcross=Zcrosscos(φu,i)=Vcross,rms2Icross,rms⋅cos(φu,i)=V1,rms2+V2,rms2Icross,rms⋅cos(φu,i)

[0026] Based on the currents, the power signals supplied by one of the two outputs can be determined using the following formula. P1=V1⋅I1⋅cos(φ)+Vcross⋅Icross⋅cos(φ)=V1⋅I1⋅cos(φ)+(V2−V1)⋅Icross⋅cos(φ) P2=V2⋅I2⋅cos(φ)+Vcross⋅Icross⋅cos(φ)=V2⋅I2⋅cos(φ)+(V2−V1)⋅Icross⋅cos(φ)

[0027] The input and output signals of the controller are measured as the root mean square (RMS) values ​​of the individual parameters, with a sampling time equal to the period of a sliding window. Due to the impedances, it is recommended to calculate the power as a function of the resistances. The average power can then be calculated as follows. P1,avg=V1,rms2RB1+V2,rms2+V1,rms2Rcross=RB1+RcrossRB1⋅Rcorss⋅V1,rms2+1Rcross⋅V1,rms2 P2,avg=V2,rms2RB2+V2,rms2+V1,rms2Rcross=1Rcross⋅V1,rms2+RB2+RcrossRB2⋅Rcorss⋅V2,rms2

[0028] For a system with two bipolar electrosurgical instruments, the actual operating currents are determined analogously to the determination in a monopolar system. According to Kirchhoff's current law, the following applies to the cross currents: Icross1=−Icross2=Iw1−I1

[0029] The sum of the transverse resistances Rcross1 and Rcross2 is calculated according to the following equation Rcross1+Rcorss2=V1,rms2+V2,rms2Icross1,rms⋅cos(φu,i)

[0030] Assuming that Rcross1 even Rcross2 It is assumed that the corresponding stresses Vcross1 and Vcross2 how to relate as follows Vcross1=−Vcross2=12⋅(V2−V1)

[0031] The average power output of each instrument is determined according to the following formula. P1,avg=V1,rms2RB1+Vcross1,rms2Rcross1=V1,rms2RB1+(V1,rms2+V2,rms2)2⋅(Rcross1+Rcross2) P2,avg=V2,rms2RB2+Vcross2,rms2Rcross2=V2,rms2RB2+(V1,rms2+V2,rms2)2⋅(Rcross1+Rcross2)

[0032] The performance of each instrument is compared with the respective reference performance and can be regulated by means of a power control system.

[0033] In current control, the RMS values ​​of the output currents I1 and I2 of each instrument can be controlled by manipulating the output voltages.

[0034] In voltage regulation, the output voltages are compared with the voltage drop of the transverse impedance(s), and the maximum is used as the controlled variable, which is influenced by the output voltages themselves.

[0035] A key advantage of the invention is that this occurs at two different frequencies, f1 and f2. This doubles the number of available coefficients, allowing the observer unit to calculate not only the measurable total current but also the non-measurable operating current flowing through the electrosurgical instrument into the tissue being treated. This enables a previously unattainable level of precision and granularity in current determination.

[0036] As can easily be seen, further electrical parameters such as voltages, including a transverse voltage, and / or other currents, preferably a transverse current, can be determined taking into account the first and second operating currents. The root mean values ​​(RMS) for the respective currents, voltages, and powers can also be determined.

[0037] Advantageously, the observer unit also includes a phase angle determination module configured to determine the phase angle between the voltage and the first and / or second current of the first and / or second output, respectively. This allows for proper consideration of the phase shift between voltage and current at both outputs. This is important for assessing the active power and, consequently, the energy transferred to the tissue by the electrosurgical instruments. Furthermore, the phase angle determination module facilitates the determination of the RMS value.

[0038] For efficient calculation of the Fourier transform, the observer unit advantageously includes a device for processing the measured values ​​using a sliding window. Advantageously, the sliding window has a variable length, which is preferably determined as a function of the first frequency, the second frequency, and a frequency difference between the first and second frequencies. This allows the length of the sliding window to be adapted to the frequencies used. For reasons of computational efficiency, a fast (FFT) or discrete (DFT) Fourier transform can preferably be used, although this is not strictly necessary.

[0039] Preferably, the sliding window device includes a common divider calculation unit and is preferably configured such that the reciprocal of a common divider is used for the length of the sliding window. This allows the sliding window to be adapted to the frequencies, thereby reducing unwanted spectral leakage. It is particularly advantageous to use the reciprocal of the largest (or second largest) common divider for the length of the sliding window. This results in a short window, which represents an optimum in terms of frequency resolution and the avoidance of spectral leakage.

[0040] Although the actual current flowing through the electrosurgical instrument is the more important parameter, it can also be advantageous to consider the cross-current. For this purpose, a cross-current detector is advantageously provided, configured to detect any cross-current between the first and second outputs when activated. This allows for a more accurate calculation of the total output power of the electrosurgical generator at its dual output. Furthermore, it enables adequate consideration of the cross-current. The cross-current detector is also preferably connected to a cross-current controller, configured to adjust the electrical characteristics, in particular the voltage, current, and / or frequency, of the second RF generating unit to control the cross-current.

[0041] Preferably, the power of the first and second RF generation units is controlled independently of each other by a first and second RF generation controller, respectively, with the first and second operating current, and optionally also the cross-current (and / or the respective impedances), being used as input variables. The use of independent controls enables a highly specific response to varying impedances at the electrosurgical instruments, particularly due to differing tissue properties to which the respective electrosurgical instrument is applied. The load impedance of the treated tissue is an important parameter and can be easily calculated by dividing the measured voltage by the operating current determined by the observer unit.It is advantageous if the first and second generation controllers are capable of applying different control laws, preferably "current control" and / or "power control," and optionally also "voltage control." It is particularly preferred if the different control laws can be applied selectively, especially depending on the load and / or power of the respective electrosurgical instrument. It is particularly preferred if more than one control law is processed, the outputs of the individual control laws are compared, and one is selected. For example, a deviation between the actual and setpoint values ​​is determined for each, and the control law with the smallest deviation is used by a selection device to determine the setpoint for further control. "Current control" aims to maintain a current and thus the tissue effect achieved by the electrosurgical instrument.It is particularly useful for relatively low load impedances. The "power control" enables precise control of the energy delivered to the electrosurgical instrument per unit of time. It takes into account the calculated values ​​for the operating current and the cross-current, as specified in the power equations for P1 and P2 shown above. It is especially useful for medium load impedances at the electrosurgical instrument. For relatively high load impedances at the electrosurgical instrument, a "voltage control" is provided, for example, to ensure that the output and applied voltages remain within safe limits for the electrosurgical instrument and the patient. The various control rules can be used individually or in parallel, for example, current control with subordinate voltage control.A decoupling control is preferably provided, designed for independent control of the first and second RF generation units, with the decoupling control interacting with the observer unit. This allows the observer unit, and in particular the calculated operating currents, to decouple the control of the electrosurgical instruments at the two outputs. This minimizes or eliminates adverse interference between the first and second electrosurgical instruments, even when they are electrically connected via the cross-current. This is a significant advantage when using appropriate control. It is important to note that the first and second RF generation units can operate independently, including being configured to apply different control laws.

[0042] It should also be possible for these first and second RF generation units to be configured as a combined unit capable of outputting both the first and second high-frequency AC voltages independently. The first and second frequencies can be generated with different voltages and frequencies by a single combined unit. For this purpose, the combined unit is preferably a multilevel inverter with a plurality of inverter cells, wherein a first group of the plurality of inverter cells is configured to generate the first high-frequency AC voltage and a second group of inverter cells is configured to generate the second high-frequency AC voltage. This allows the first and second frequencies for dual output to be generated very efficiently, and the same inverter can alternatively be used with all inverter cells in a group when only one output is required.This results in increased operational flexibility with minimal effort.

[0043] A multilevel inverter is an inverter unit that can output a voltage at different levels, rather than just a simple on / off output with positive and / or negative polarity. Typical topologies include cascaded H-bridges, neutral clamping, and flying capacitors.

[0044] For practical purposes, it is advantageous if the first frequency, the second frequency, and the frequency difference between the first and second frequencies are chosen such that their respective values ​​are composite numbers, i.e., not prime numbers. Since they are not prime numbers, a fairly large common divisor can be defined for the first, second, and differing frequencies, which allows for a relatively short sliding window length to achieve good spectral resolution and minimize spectral leakage.

[0045] The invention is explained in more detail below with reference to an advantageous embodiment. In the figures: Fig. Figure 1 shows a frontal view of an electrosurgical generator with two electrosurgical instruments attached to it; Fig. Figure 2 shows a schematic representation of several electrosurgical instruments at the surgical site; Fig. Figure 3 shows a schematic functional diagram of the electrosurgical generator with two monopolar output sockets; Fig. 4 shows a close-up of an observer unit; Fig. Figure 5 shows an equivalent circuit diagram and currents for two outputs supplying two monopolar electrosurgical instruments; Fig. Figure 6 shows the currents for the output of two different frequencies and a resulting beat frequency; Fig. Figure 7 shows a performance diagram with different control zones; Fig. Figure 8 shows a schematic functional diagram of another embodiment of the electrosurgical generator with a combined high-frequency generation unit; and Fig. Figure 9 shows an equivalent circuit diagram and currents for two outputs supplying two bipolar electrosurgical instruments.

[0046] An exemplary embodiment of an electrosurgical generator according to a first embodiment of the present invention is shown in Fig. Figure 1 shows the electrosurgical generator, designated as a whole by reference numeral 1, comprising a housing 11 with at least two output sockets 16, 16' (and optionally an additional socket 17 for a neutral electrode) for connecting electrosurgical instruments 19, 19'. A power supply cable 12 is provided with a plug for connection to an electrical power source (not shown), which may be a mains power supply, such as the AC mains in a building, or an off-grid power source, such as a 12-volt or 24-volt battery in a vehicle or mobile hospital. Furthermore, a user interface 14 is provided, which includes a display 15, which may be a touchscreen, or buttons 13 for user input.

[0047] The electrosurgical instrument 19 includes a cable 18, which is to be plugged into the output socket 16 to supply high-frequency alternating voltage for the operation of the electrosurgical instrument 19. This also applies to the other electrosurgical instrument 19', which is to be connected to the output socket 16' with its cable 18'.

[0048] The two electrosurgical instruments 19, 19' to be supplied by the electrosurgical generator 1 are in Fig. Figure 2 shows an operating room. An operating table 98 is provided, which is set up to accommodate a patient 99 to be treated. In the illustrated embodiment, both electrosurgical instruments 19, 19' are to be used at different locations on the same patient 99. In the illustrated embodiment, both electrosurgical instruments 19, 19' are of the monopolar type. This requires a neutral patch electrode 10, which is attached to the operating table 98 or preferably to the patient 99, thus creating a relatively large contact area. The neutral patch electrode 10 is connected via a cable 10' to the auxiliary socket 17 of the RF generator 1, thereby creating a return path and closing the circuit for the RF energy supplied by the RF generator 1 to the RF instruments 19, 19'.

[0049] A schematic functional diagram of the electrosurgical generator is shown in Fig. Figure 3 shows the electrical energy being supplied to a power supply unit 20 of the electrosurgical generator 1 via the power supply cable 12. The power supply unit provides the various devices, units, and modules of the electrosurgical generator 1 with electrical energy, in the illustrated embodiment with direct current. In particular, it supplies a first RF generation unit 4 with electrical energy via a DC bus 22 for generating a first high-frequency alternating voltage, which is fed via a first output line 23 and a first sensor arrangement 26 for voltage and current measurement to a first output socket 16 (for simplicity also referred to as output 16) to supply the inserted electrosurgical instrument 19. The output line 24 consists of an active electrode line (AE) 24 and a neutral electrode line (NE) 25.The high voltage is typically in the range of a few kilovolts, but can also exhibit amplitudes in the range of a few tens of volts up to 4000 volts. Furthermore, a second RF generation unit 4' is provided, which is also supplied by the power supply 20 via the DC bus 22 and is equipped with a second output line 23' for outputting voltage in the same manner, wherein the second output line 23' comprises an active electrode line 24' and a neutral electrode line 25', as well as a second sensor arrangement 26' for voltage and current measurement at a second output socket 16'.In the illustrated embodiment, a monopolar configuration is shown, in which the output jacks 16, 16' are configured as unipolar outputs for connecting a monopolar instrument 19, 19', and in which the neutral electrode (NE) leads 25, 25' are connected to the additional neutral output jack 17, to which the neutral patch electrode 10 is connected. A second embodiment is provided for bipolar outputs, as shown in [reference]. Fig. 8 and Fig. 9 shown.

[0050] The operation of the first and second RF generation units 4, 4' is controlled by a central control unit 2, which in turn is connected to the user interface 14, allowing the user to issue instructions and commands for the operation of the electrosurgical generator 1. The central control unit 2 generates corresponding control signals and, according to these instructions and commands, controls the relevant devices, units, and modules of the RF generator 1. The central control unit 2 includes, in particular, a common inverter controller 3, which supplies command signals to a first and second RF generation controller 41, 41', each of which in turn controls its respective first and second RF generation unit 4. The first RF voltage generated by the first RF generation unit 4 is routed to the output socket 16 via the respective output line 23 and the sensor arrangement 26.Likewise, the second high-frequency voltage generated by the second RF generation unit 4' is routed to the output socket 16' via the respective output line 23' and the sensor arrangement 26'.

[0051] The first and second RF generation units 4, 4' generate the first and second RF voltages, respectively, with a voltage and frequency specified by the respective first and second RF generation controllers 41, 41'. The voltage and frequency of the first and second RF generation units 4, 4' can be controlled and generated independently. However, the resulting current delivered by the first and second RF generation units 4, 4' via their respective output sockets 16, 16' is determined by the impedance of the respective electrosurgical instrument 19, 19' and the tissue contacted by both instruments. The total current I1 flowing through the first output socket 16 is determined by the first sensor arrangement 26, which also determines the respective actual voltage; likewise, the total current I2 flowing through the second output socket 16' is determined by the second sensor arrangement 26', which also determines the respective actual voltage.The resulting measurement signals are fed to a signal processing unit 9, which may include an analog-to-digital converter (ADC), and are fed back to the central control unit 2 via a current calculation device 5.

[0052] However, the total current I1 determined by the respective sensor unit 26, 26' is not identical to the current flowing through the tissue on which the electrosurgical instrument is applied ("working current").

[0053] As in Fig. As shown in Figure 2, the electrosurgical instruments 19, 19' are normally attached to different locations on the patient's body. These locations can be quite close together, especially in assisted procedures, or they can be relatively far apart, especially in co-operations. In any case, the current delivered from the output 16 of the electrosurgical instrument 19 not only takes the desired path through the tissue being treated to the neutral electrode 10, but also flows as a so-called cross current to the other electrosurgical instrument 19'. The same applies to the current delivered from the output 16' of the electrosurgical instrument 19' with respect to a cross current to the electrosurgical instrument 19.

[0054] This is in Fig. Figure 5 shows an equivalent circuit diagram for the case of two monopolar electrosurgical instruments 19, 19' with a common neutral electrode 10. In this equivalent circuit, two voltage sources are shown on the far left and far right, symbolizing the first high-frequency generating unit 4, which outputs an alternating voltage V1 with a first frequency f1, and the second high-frequency generating unit 4', which outputs an alternating voltage V2 with a first frequency f2. Because the high-frequency generating units 4, 4' output different frequencies, a beat frequency is generated.

[0055] This is also in Fig. Figure 6 shows the first high-frequency generating unit producing a voltage V1 with the first frequency f1, and the second high-frequency generating unit 4' producing a voltage to with the second frequency f2. These voltages are represented by the large-amplitude waves (both frequencies are quite similar; they are barely distinguishable in the figure because they both have the same amplitude). The resulting beat frequency is represented by the lower-amplitude waves. This beat frequency arises from cross-coupling caused by a transverse impedance of the patient's body 99, as shown below.

[0056] The total current I1 supplied from output 16 and flowing via cable 18 to the electrosurgical instrument 19 is shown in the upper left corner of the subdiagram, and the total current I2 supplied from output 16' and flowing via cable 18' to the other electrosurgical instrument 19' is shown in the upper right corner of the subdiagram. As can easily be seen, the current flow is influenced by the beat frequency.

[0057] Each current supplied by one of the two high-frequency generating units 4, 4' is divided into a part I cross , which flows through a transverse impedance formed by the patient body 99 to the respective other high-frequency generating unit 4', 4, and another part I w1 or I w2 , which is determined by the respective tissue impedance Z w1 , Z w2to the common neutral patch electrode 10 (and finally back to the high-frequency generation units 4, 4'). These are the currents flowing through the tissue impedance I w1 and I w2 , which must be properly controlled for effective treatment. However, these currents can be affected by the existing cross-current I. cross They cannot be measured directly. Only the total current I1 and I2 supplied by the respective high-frequency generating unit 4, 4' can be measured directly.

[0058] In order to correctly control the power and energy delivered by the respective electrosurgical instrument 19, 19' to the tissue to be treated, the respective working currents I w1 or I w2 These values ​​are known. However, as already mentioned, they cannot be measured directly. To enable proper control, the invention provides a working current calculation device 5, which is used for the indirect determination of I.w1 or I w2 is designed by means of an observer unit 6 which receives measurable quantities as input quantities. Likewise, the cross-current I cross The data is determined and then used for current and power control.

[0059] As in Fig. 2 and Fig. As shown in Figure 4, the measured values ​​for the total currents I1 and I2, as well as the measured voltages of the respective outputs 16, 16', are acquired by the respective sensor arrangements 26, 26' and the measured values ​​are made available to a signal conditioning unit 19, which in particular includes an analog-to-digital converter (ADC), and subsequently to the observer unit 6. The processing of the sampled data is carried out by a sliding window of the device 7. The length of the sliding window used is variable and depends on the first frequency f1, namely the frequency of the voltage generated by the first high-frequency generation unit 4, and on the second, different frequency f2, namely the frequency of the voltages generated by the second high-frequency generation unit 4', as well as on a frequency difference Δf between the first and second frequencies. Based on these values, their common dividers are calculated by a common divider device 70.Based on the common divisors thus determined, the length of the sliding window is defined by the reciprocal of the – preferably largest – common divisor. An illustrative example (with exaggerated numbers for better understanding) has a first frequency f1 of 300 kHz, a second frequency of 400 kHz, resulting in a Δf of 100 kHz. The largest common divisor of these numbers is 100 kHz, which leads to a window length of 10 µs (10. -5s) leads to. Assuming a sampling frequency of 150 M / s, this results in 150 M / s * 10 µs = 1500 samples for the window length. This allows for a relatively short window length, enabling high spectral resolution with minimal spectral leakage. The resulting windowed data are fed to a Fourier series approximation device 61 and an automatic coefficient determination device 62, which is configured to calculate coefficients for the Fourier series approximation device 61.

[0060] The automatic determination of the coefficients for the Fourier series as well as a Fourier transformation is carried out by the Fourier series approximation device 61 and the automatic coefficient determination device 62, as shown below:

[0061] Based on the measured total current I1 supplied from output 16 to the first electrosurgical instrument 19, the Fourier coefficients for a first-order Fourier series with offset are determined to calculate the operating current I w1 to obtain: a1,0(k)=2K∑k−KkI1(k) a1,1(k)=2K∑k−KkI1(k)⋅cos(2⋅π⋅f1⋅k⋅Δ) b1,1(k)=2K∑k−KkI1(k)⋅cos(2⋅π⋅f1⋅k⋅Δ)

[0062] This is performed by the automatic coefficient determination device 62. Likewise, the coefficients of a corresponding Fourier series relating to the operating current I are determined. w2 of the second electrosurgical instrument 19', determined by the automatic coefficient determination device 62: a2,0(k)=2K∑k−KkI2(k) a2,1(k)=2K∑k−KkI2(k)⋅cos(2⋅π⋅f1⋅k⋅Δ) b2,1(k)=2K∑k−KkI2(k)⋅sin(2⋅π⋅f1⋅k⋅Δ)

[0063] These coefficients are forwarded by the automatic coefficient determination device 62 to the Fourier approximation device 61, which in turn calculates the working currents using a first-order Fourier series: Iw1(k)=a1,0,f1+a2,0,f12+(a1,1,f1+a2,1,f1)⋅cos(2⋅π⋅f1⋅k⋅Δ)+(b1,1,f1+b2,1,f1)⋅sin(2⋅π⋅f1⋅k⋅Δ) Iw2(k)=a1,0,f2+a2,0,f22+(a1,1,f2+a2,1,f2)⋅cos(2⋅π⋅f2⋅k⋅Δ)+(b1,1,f2+b2,1,f2)⋅sin(2⋅π⋅f2⋅k⋅Δ)

[0064] This allows values ​​for the - not directly measurable - currents I to be obtained with the help of the Fourier series approximation device 61 using the automatically determined coefficients. w1 and I w2 These values ​​are obtained. They are transmitted to the central control unit 2, in particular its common inverter control 3, by means of a multiparameter signal 69, which preferably also contains measurement signals for the voltage measured at one of the two outputs 16, 16'. This enables the calculation of the power.

[0065] Furthermore, the observer unit 6 is equipped with a phase angle determination module 65. This module is configured to determine a phase angle φ between the voltage and the first and / or second current I1, I2 of the first and second outputs 16, 16', respectively. In this way, an actual phase difference φ at one of the two outputs 16, 16' can be determined, allowing the phase shift between the voltage and current supplied to the electrosurgical instrument 19, 19' at the respective first and second outputs 16, 16' to be adequately accounted for. This is essential for evaluating the active power and thus the energy transferred from the electrosurgical instruments to the tissue. Furthermore, the RMS values ​​can be determined using the phase angle φ provided by the phase angle determination module 65.

[0066] The common inverter control 3 is further equipped with a cross-current controller 8. This is communicatively connected to a cross-current detector 80, to which data from the observer unit 6, in particular its Fourier series approximation device 61, are supplied. This allows the presence of a cross-current I to be detected. crossThe current is detected and corresponding signals are supplied to the cross-current controller 8. The cross-current controller 8 works in conjunction with the common inverter control 3 to modify the control of the high-frequency generation units 4, 4', in particular their respective RF generation controls 41, 41', in order to control their power taking the cross-current into account. This can be achieved, for example, by current control, since the effect on the tissue is determined by the total current resulting from the sum of the operating current and the cross-current. Similarly, power control can utilize the cross-current, since the total power acting on the tissue is the sum of the power delivered to the body impedance Zw1 or Zw2 and to the cross-impedance Zcross. Furthermore, in voltage control, the tissue is affected by the maximum voltage drop across the body impedance Zw1 or Zw2 and Zcross.

[0067] With the work flows thus determined I w1and I w2 Different control laws are implemented in the common inverter control 3 and in the first and second RF generation control 41, 41'. Based on the operating current determined by the observer unit 6, the actual load impedance for each electrosurgical instrument 16 can be easily determined by taking the respective measured voltage V1 for the electrosurgical instrument 16 and dividing it by the determined operating current I. w1 (Voltage V2 divided by operating current I) w2 in the case of the second electrosurgical instrument 19') is divided. In Fig. Figure 7 shows a performance diagram with different control ranges. Three embodiments are shown, in which up to three control laws are implemented. Preferably, the different control laws are to be used sequentially, particularly depending on the load and / or power of the respective electrosurgical instrument 19, 19'. It should be noted that, due to the independent first and second RF generation controls 41, 41', the two RF generation units 4, 4' can be operated with different control strategies and control laws.

[0068] In a first embodiment, represented by the upper solid line, current control can be advantageous at relatively low load impedances, which in the illustrated embodiment are, for example, less than approximately 200 Ω, as it aims to achieve a defined operating current. At medium load impedances, in the illustrated embodiment, for example, in the range between approximately 200 Ω and approximately 500 Ω, power control can be advantageous to maintain a defined operating current. At higher load impedances, greater than approximately 500 Ω (up to approximately 2000 Ω, where the control law ends), voltage control is preferably used to prevent overvoltages. This control sequence is applicable when the electrosurgical generator is permitted to operate at full power. If the power is limited (e.g.,(at "half power"), the lower solid line with "power control" applies to any load impedance below approximately 1000 Ω; above that, it switches to "voltage control".

[0069] In a second embodiment, represented by the long dashed line, which is used, for example, for a different generator mode for a different surgical application, "current control" is performed for load impedances below approximately 200 Ω, while above this threshold the system switches to "voltage control".

[0070] In a third embodiment, represented by the dotted line, which is used, for example, for another generator mode for a different surgical application, a "current control" is performed for load impedances below approximately 200 Ω, then briefly switched to a "power control" whereby the power decreases linearly with increasing load impedance, and then switched to a "voltage control" for any higher load impedance at approximately 300 Ω.

[0071] In Fig. Figure 8 shows a schematic functional diagram of another embodiment of the electrosurgical generator. This embodiment has a bipolar configuration for bipolar electrosurgical instruments, in which the output sockets 16, 16' are configured as bipolar outputs for the respective connection of a bipolar instrument 19, 19', each output socket 16, 16' being supplied by output lines 23, 23', which have their own pair of lines for active electrodes (AE) and neutral electrodes (NE).

[0072] Another difference from the embodiment of Fig. 3 consists in the fact that the embodiment of Fig. Figure 8 features a combined high-frequency generation unit 4*, which replaces the two separate high-frequency generation units 4 and 4'. It is designed as a multilevel inverter with a plurality of inverter cells 4-1, 4-2, 4-3, and 4-4. In a first state, the inverter cells 4-1, 4-2, 4-3, and 4-4 are cascaded and divided into two groups (e.g., two inverter cells each, but other distributions between the groups are also possible), with each group connected to one of the outputs 16 and 16'. The inverter cells of each group generate the high-frequency alternating voltage for their respective output 16 and 16'. The RF generation for both groups is controlled by the combined RF generation controller 4*, which thus assumes the functionality of the first and second RF generation controllers 41 and 41'. However, the provision of the combined high-frequency generation unit 4* is independent of the bipolar configuration.The combined high-frequency generation unit 4* can also be configured for a monopolar configuration of the output jacks, as shown in . Fig. 3 shown, and the bipolar configuration can also be applied to the two separate high-frequency generating units 4, 4', as in Fig. Figure 3 shows. Furthermore, a mixed arrangement for a monopolar and a bipolar output socket and corresponding electrosurgical instruments is possible.

[0073] As an additional advantage, this combined high-frequency generation unit 4* (in its first state) allows the ungrouping and configuration of all inverter cells 4-1, 4-2, 4-3, 4-4 in a cascade, thereby supplying only one output 16 with double the voltage range and double the power. This switching between the first and second states is controlled by a cell configuration controller 45, which is controlled by the central control unit 2. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3 912 580 A1

[0006]

Claims

[1] Electrosurgical generator for outputting a high-frequency alternating voltage to electrosurgical instruments, comprising a first RF generation unit (4) which supplies a first high-frequency alternating voltage with a first frequency to a first output (16), a second RF generation unit (4') which supplies a second high-frequency alternating voltage with a second frequency which is different from the first frequency to a second output (16'), wherein the first and second outputs are designed to connect a first and second electrosurgical instrument (19, 19') such that, in an activated state, a first current flows through the first electrosurgical instrument and, at the same time, a second current flows through the second electrosurgical instrument, and a central control unit (2) which is designed to control the operation of the electrosurgical generator (1) including an inverter control (3) for the operation of the first and second RF generation unit (4, 4'), characterized by , that the inverter controller (3) is designed such that it receives calculated operating currents as an input signal, wherein the operating currents are obtained by an operating current calculation device (5) which is communicatively connected to the inverter controller (3), wherein the operating current calculation device (5) comprises an observer unit (6) which is designed for an indirect determination of the first and the second operating current based on measured values obtained by a double measurement of the actual output currents at the first and the second output (16, 16'). [2] Electrosurgical generator according to claim 1, characterized byin that the observer unit (6) is provided with a Fourier series approximation device (61) for actually calculating a dual Fourier series approximation, one for the first operating current and one for the second operating current, and further comprises an automatic coefficient determination device (62) which is designed to calculate coefficients of the Fourier series approximation based on the measured values of the output currents (16, 16'). [3] Electrosurgical generator according to the preceding claim, characterized by that other currents, preferably a cross-current, and voltages, preferably a cross-voltage, are to be determined taking into account the first and second working currents and / or effective values (RMS) for the respective currents, voltages and powers are to be measured and calculated. [4] Electrosurgical generator according to one of the preceding claims, characterized byin that the observer unit (6) further comprises a phase angle determination module (65) which is designed to determine a phase angle between the voltage and the first and / or second current of the first and second outputs (16, 16'), respectively. [5] Electrosurgical generator according to one of the preceding claims, characterized by that the observer unit (6) further comprises a sliding window device (7) for data processing of the measured values, wherein the sliding window preferably has a variable length. [6] Electrosurgical generator according to the preceding claim, characterized by that the variable length is determined as a function of the first frequency, the second frequency and / or a frequency difference between the first and the second frequency. [7] Electrosurgical generator according to the preceding claim, characterized bythat the sliding window device (7) comprises a device (70) for calculating the common divisor and is preferably designed to use a reciprocal of the, in particular largest, common divisor for the length of the sliding window. [8] Electrosurgical generator according to one of the preceding claims, characterized by that a cross-current detector (80) is provided which is designed to determine a cross-current between the first and the second output (16, 16') in an activated state. [9] Electrosurgical generator according to the preceding claim, characterized by that the cross-current detector (80) cooperates with a cross-current controller (8) which is designed to adjust electrical properties, in particular voltage, current and / or frequency, of the second RF generation unit (4') such that the cross-current is controlled. [10] Electrosurgical generator according to one of the preceding claims, characterized by that the output of the first and second RF generation units (4, 4') is controlled independently of one another by a first and second generation controller (41, 41'), respectively, preferably using the first and second operating currents as input variables, wherein further preferably a decoupling controller (9) is provided which is designed for the independent control of the first and second RF generation units (4, 4') and which interacts with the observer unit (6). [11] Electrosurgical generator according to the preceding claim, characterized by that the first and second generation controllers (41, 41') are designed to apply different control laws, preferably current control, voltage control and / or power control. [12] Electrosurgical generator according to the preceding claim, characterized bythat the various control laws are to be applied selectively, in particular depending on the load and / or power of the respective electrosurgical instrument (19, 19'). [13] Electrosurgical generator according to one of the preceding claims, characterized by that the first frequency, the second frequency and the frequency difference between the first and the second frequency are chosen so that their respective values are a composite number, i.e. not a prime number. [14] Electrosurgical generator according to one of the preceding claims, characterized by that the first and second RF generation units (4, 4') are designed as a combined unit (4*) which is suitable for outputting the first and second high-frequency alternating voltages at the first and second outputs, respectively. [15] Electrosurgical generator according to the preceding claim, wherein the combined unit (4*) is a multilevel inverter having a plurality of inverter cells (4-1, 4-2, 4-3, 4-4), wherein a first part of the plurality of inverter cells (4-1, 4-2) is configured to generate the first high-frequency AC voltage, and a second part of the plurality of inverter cells (4-3, 4-4) is configured to generate the second high-frequency AC voltage.

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