Electrosurgical Generator

Abstract

To enable dual activation while avoiding unwanted interference.SOLUTION: In an electrosurgical generator, an inverter unit is configured for simultaneous activation of electrosurgical instruments connected to each of at least two output sockets and comprises a plurality of co-operating inverter cells. The plurality of inverter cells is connected in a cascaded manner in a first state and is split into at least two groups in a second state. Each of the at least two groups is assigned to at least one of the two output sockets and feeds its generated output voltage, high-frequency alternating voltage, via electrode lines to the assigned output socket. The inverter cells are commonly controlled by synchronized reference signals being generated by a common control unit.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrosurgical generator configured to output a high frequency alternating current voltage to at least one electrosurgical instrument, the electrosurgical generator comprising an inverter unit that generates a high frequency alternating current voltage that is supplied to at least two output sockets configured for simultaneous connection of electrosurgical instruments. [Background technology]

[0002] In electrosurgery, or radiofrequency surgery, electrosurgical instruments, such as electrocauteries, are used to apply high-frequency alternating current to tissue in the human body. Radiofrequency waves, typically in the radiofrequency range from approximately 200 kHz up to 4,000 kHz, are used. This results in localized heating of the tissue, which is then thermally cut or torn, and the tissue is removed by thermal ablation. The primary advantage of this is that bleeding can be stopped simultaneously as the cut is made by closing the affected blood vessels, allowing the electrosurgical instrument to be used for other purposes, such as coagulation. Different types of applications require different electrosurgical instruments.

[0003] Some applications may require the simultaneous use of two or more electrosurgical instruments, particularly two, to perform a surgical task (dual activation). To make this feasible, separate electrosurgical generators may be used, one for each electrosurgical instrument. A typical problem encountered is the potential for interference between the high-voltage outputs generated by the electrosurgical generators. Such interference can include undesirable low-frequency beating, similar to the phenomenon encountered in acoustic fields when two frequencies are close to each other but not perfectly matched. Such low-frequency beating is detrimental to the stable operating conditions of the electrosurgical instruments. This is particularly true when two separate electrosurgical generators are used, but it can also be encountered when a single electrosurgical generator with dual output stages and inverters is employed, thereby enabling dual activation of electrosurgical instruments. However, avoiding unwanted interference remains difficult. Summary of the Invention [Problem to be solved by the invention]

[0004] It is therefore an object of the present invention to provide an improved electrosurgical generator that allows for dual activation while avoiding undesired interference. [Means for solving the problem]

[0005] The solution according to the invention consists in an electrosurgical generator according to the features of the independent claims. Advantageous developments are the subject of the dependent claims.

[0006] The present invention provides an electrosurgical generator configured to output a high-frequency AC voltage to an electrosurgical instrument, comprising an inverter unit that generates a high-frequency AC voltage that is supplied to at least two output sockets for connection of electrosurgical instruments, the inverter unit being configured to simultaneously activate the electrosurgical instruments connected to each of the at least two output sockets and comprising a plurality of inverter cells that cooperate with each other, the plurality of inverter cells being cascaded in a first state and divided into at least two groups in a second state, each group being assigned to one of the at least two output sockets and supplying an output voltage that is the generated high-frequency AC voltage to the assigned output socket via an electrode wire, and being commonly controlled by a synchronized reference signal generated by a common control unit.

[0007] Modern electrosurgical generators employ inverters comprising multiple inverter cells. The inverter cells are typically connected in series to provide the high HF voltage required to power electrosurgical instruments. An electrosurgical generator comprising such an inverter is the subject of the applicant's unpublished patent application, filed under DE 102021122282 A1. This allows for more efficient and versatile generation of high-frequency AC voltages. In particular, the generated high-frequency AC voltage is determined by a reference signal used to control the inverter cells, thereby providing positive control over the frequency, phase, and optionally also the shape of the generated AC voltage.

[0008] In the following, some expressions used within the context of the present invention are explained.

[0009] The inverter unit is a device for providing an actual high frequency AC voltage output to an electrosurgical instrument connected to an output socket. The inverter unit comprises a plurality of inverter cells connected to each other to supply the high frequency high voltage required by the electrosurgical instrument. The frequency, phase, and usually also the amplitude of the high frequency AC voltage generated by the inverter unit are controlled by a reference signal such as that used by the controller unit.

[0010] In the context of this application, the term "high frequency" relates to frequencies in the radio frequency range of 200 kHz to 4000 kHz generated by the inverter of an electrosurgical generator. However, in electrosurgical generators capable of driving ultrasonic instruments, the term "high frequency" also relates to the ultrasonic frequency range of 20 kHz to 200 kHz (ultrasonic surgical generators). High frequency AC voltages are typically high voltages. In the context of this patent, high voltages are considered to have amplitudes in the high voltage range, particularly up to 10 kV, preferably up to 4000 volts, and even more preferably above 100 volts.

[0011] The present invention utilizes an inverter configured as a stacked multi-cell inverter, allowing multiple inverter cells to be intentionally divided into at least two different groups, each providing a single output. The multiple inverter cells, and thus the different groups, are under common control, allowing synchronization of the different groups and the high-voltage outputs provided by each group. Therefore, both outputs are effectively synchronized, avoiding undesirable interference patterns. As a result, the low-frequency beating that adversely affects the co-activation of two or more electrosurgical instruments using conventional approaches is effectively eliminated. This allows for much better control of the thermal energy and cutting force of the electrosurgical instruments, thereby improving the quality of work performed by surgeons using the electrosurgical instruments.

[0012] Furthermore, employing an inverter using multicell technology with cells divided into different groups under common control provides the added benefit of frequency stability under varying load conditions. This applies to both outputs, allowing them to remain synchronized even under difficult conditions, particularly, but not exclusively, in situations where heterogeneous tissues are treated where electrical impedance varies widely. Traditionally, this often results in frequency deviations and therefore uncontrolled beat frequencies, adversely affecting the quality of electrosurgery. Synchronous control of groups of inverter cells effectively avoids all of this.

[0013] Thus, the present invention achieves at least two major benefits for the patient: reduced risk and improved quality of surgery.

[0014] Preferably, the inverter unit is a multi-level inverter, which is capable of generating multiple voltage levels with fairly fine voltage stepping, allowing for a more controlled generation of AC voltage.

[0015] Advantageously, the reference signals are synchronized so that the output voltages have the same frequency. Providing such synchronized reference signals to groups of inverter cells ensures that the voltages generated by the groups of inverter cells are also synchronized. This synchronized frequency provides the advantage that there is no frequency difference between the high-frequency AC voltages generated by one group and the high-frequency AC voltages generated by another group. If both waveforms have exactly the same frequency, any low-frequency interference patterns can be effectively avoided. In particular, the same frequency eliminates the risk of creating a low-frequency beat condition, which by definition requires a frequency difference (which will later determine the beat frequency).

[0016] More preferably, the output voltage of one group is synchronized with the output voltage of another group with a predetermined phase shift. This synchronizes not only the frequency but also the phase between the output voltages of one group and another group. The predetermined phase shift can be zero so that the output voltages of different groups have the same frequency and phase. However, this is not necessarily the case; another suitable option is to have a 180° phase shift, i.e., opposite polarity. This allows the output voltage to be inverted relative to the output voltage of another group. Surprisingly, there are certain situations in which the opposite polarity results in improved interference characteristics.

[0017] In an advantageous embodiment, at least two groups share one of the electrode wires, in particular they share a common neutral electrode, which allows reducing the number of electrodes attached to the patient's body, and the common neutral electrode ensures that the instruments have the same neutral potential, thereby avoiding undesirable cross currents at that neutral potential.

[0018] Preferably, the output socket is configured for monopolar electrosurgical instruments, thereby allowing HF power to be supplied to two monopolar electrosurgical instruments, preferably using a shared neutral electrode. Such a configuration is beneficial because it allows dual, independent activation of both monopolar electrosurgical instruments while requiring only one additional electrode on the patient's body.

[0019] In a preferred alternative embodiment, each group has its own electrodes, particularly the active and neutral electrodes, none of which are shared with another group. This allows the attached electrosurgical instruments to be more independent, as each has its own return (neutral) electrode. It is further possible to provide suitable galvanic isolation. This allows for more independent attachment of the electrosurgical instruments of one group relative to the electrosurgical instruments of another group.

[0020] In a particularly advantageous embodiment, the output socket is configured for bipolar electrosurgical instruments. This allows dual activation of bipolar electrosurgical instruments. However, even if both electrosurgical instruments are completely galvanically isolated, cross currents may flow between the electrosurgical instruments due to the patient's body tissue forming a closed loop between the two electrosurgical instruments. It has been found that the amplitude of the cross current depends on the relative polarity of the voltages supplied to the electrosurgical instruments. Surprisingly, cross current minimization can be achieved by selectively changing the polarity of the output voltage of one of the groups. This allows for a fairly simple reduction of undesirable cross currents.

[0021] In a preferred embodiment, the device further comprises a current monitor configured to determine cross currents between the output sockets, thereby enabling detection of when cross currents occur, which can be employed by the control unit, for example, to monitor for excessive cross currents and thus provide a protection function.

[0022] Advantageously, at least one of the groups is provided with an automatic polarity switch, which is configured to cooperate with the current monitor to identify the polarity with the lowest cross current. This allows for the selection of a polarity that minimizes cross current, thereby suppressing undesirable interference. In a preferred embodiment, the automatic polarity switch cooperates with the current monitor to (i) determine the cross current in a first polarity state, (ii) then switch the polarity to a second polarity state and determine the cross current in the second polarity state, (iii) compare the cross currents in the first and second polarity states, (iv) determine which polarity state has the low cross current, and (v) select the polarity with the low cross current. This can be performed manually or, preferably, automatically, such that the polarity of at least one of the output voltages is selected to minimize cross current and, therefore, interference. A major advantage of the automatic polarity switch is that it automatically tracks to maintain a low cross current scenario, thereby providing a valuable boost to the utility of dual-activated electrosurgical instruments.

[0023] Preferably, the system further includes a beat frequency monitor configured to determine a beat frequency between the high-frequency AC voltages output from the at least two output sockets. This allows monitoring to determine whether frequency synchronization is achieved and maintained and whether at least two electrosurgical instruments attached to the output sockets can safely operate. If a beat frequency occurs, this is an indication that frequency synchronization needs to be readjusted. For this purpose, the beat frequency monitor preferably cooperates with a synchronization unit, preferably a PLL circuit, to ensure frequency and preferably phase synchronization between the at least two groups. This allows frequency synchronization and, if applicable, phase synchronization to be maintained.

[0024] Advantageous embodiments further include a switching device configured to selectively change the electrodes, particularly the neutral electrode, between a shared and a non-shared state. This allows for rapid configuration changes as needed. The neutral electrode may be switched to the shared state when required for operation, or particularly in the case of monopolar electrosurgical instruments. However, in other configurations, particularly but not limited to the use of bipolar electrosurgical instruments, it may be beneficial to have a neutral electrode and a non-shared state for more independent operation.

[0025] The invention is explained in more detail below, by way of example, in conjunction with the accompanying drawings, which show advantageous embodiments. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a front view of an electrosurgical generator with two attached electrosurgical instruments. [Figure 2] FIG. 1 is a schematic functional diagram of an electrosurgical generator including two output sockets. [Figure 3A] 1 shows a plurality of inverse cells in a first state divided into groups. [Figure 3B] 1 shows a plurality of inverse cells in a second state divided into groups. [Figure 4] FIG. 2 is a diagram showing the internal configuration of two inverter cells. [Figure 5A] FIG. 1 shows an equivalent circuit diagram for a monopolar electrosurgical instrument. [Figure 5B] FIG. 1 illustrates the current flow in a monopolar electrosurgical instrument. [Figure 6A] FIG. 1 shows an equivalent circuit diagram of a bipolar electrosurgical instrument. [Figure 6B] FIG. 1 illustrates the current flow in a bipolar electrosurgical instrument. DETAILED DESCRIPTION OF THE INVENTION

[0027] An electrosurgical generator according to an exemplary embodiment of the present invention is shown in FIG. 1. The electrosurgical generator, generally identified by reference numeral 1, comprises a housing 11 having at least two output sockets 17, 17′ (and optionally output socket 17”) for connection of electrosurgical instruments 19, 19′. A power cable 13 is provided with a plug 12 for connection to a power source (not shown), which may be a power grid such as AC mains power in a building or an off-grid electrical energy source such as a 12-volt or 24-volt battery in a vehicle or mobile hospital. Additionally, a user interface 14 may be provided with a display 15, which may be a touchscreen, or knobs 16, 16′ may be present for input by a user.

[0028] The electrosurgical instrument 19 comprises a cable having a plug 18 that plugs into the output socket 17 to supply high frequency AC voltage for the electrosurgical instrument 19. This is equally true for other electrosurgical instruments 19' that are connected to the output socket 17' by their plugs 18'.

[0029] FIG. 2 shows a schematic functional diagram of the electrosurgical generator. Power is supplied to the power supply unit 3 of the electrosurgical generator 1 by a power cable 13. The power supply unit 3 supplies power, in the illustrated embodiment, as DC power, to the various components, units, and modules of the electrosurgical generator 1. In particular, it supplies power via a DC bus 30 to an inverter unit 4 configured to generate a high-frequency AC voltage, which is then supplied to an output socket 17 for supplying a plugged-in electrosurgical instrument 19 via a filter 36, a step-up transformer 37, and a sensor device 38 for voltage and current measurement. The high voltage is typically in the range of several kilovolts, but may have an amplitude ranging from a few tens of volts to 4,000 volts. Additionally, the inverter unit 4 is provided with a second branch for similarly outputting a voltage to the output socket 17' via a filter 36', a step-up transformer 37', and a sensor device 38'.

[0030] The operation of the inverter unit 4 is managed by a master controller 2 connected to a user interface 14, allowing a user to issue instructions and commands for the operation of the electrosurgical generator 1. The master controller 2 generates corresponding control signals and manages the associated components, units, and modules of the electrosurgical generator 1 in accordance with these instructions and commands. In particular, the master controller 2 provides command signals to a common control unit 6, which controls the inverter cells of the inverter unit 4. In the illustrated exemplary embodiment, four inverter cells 5-1, 5-2, 5-3, and 5-4 are provided. The generated high-frequency AC voltage is output by the inverter unit 4 to two electrode wires comprising an active electrode 33 and a neutral electrode 34, and then passes through a filter 36, a step-up transformer 37, and a sensor device 38 to an output socket 17. Similarly, a second high-frequency AC voltage is generated by the inverter unit 4 and supplied by two electrode wires comprising an active electrode 33' and a neutral electrode 34', and then passes through a filter 36', a step-up transformer 37', and a sensor device 38' to an output socket 17'.

[0031] The generation of high frequency AC voltage by inverter unit 4 and its supply to output socket 17 or, as the case may be, output sockets 17, 17' will be described below with reference to Figures 2 and 3A-3B. As shown, inverter unit 4 comprises a plurality of inverter cells 5-1, 5-2, 5-3, 5-4 driven by a common control unit 6. Inverter cells 5-1, 5-2, 5-3, 5-4 are supplied with a DC voltage from power supply unit 3, in this case a DC voltage of 48 V. This DC voltage is supplied to all of inverter cells 5-1, 5-2, 5-3, 5-4. A reference signal generated by common control unit 6 and carried to inverter cells 5-1, 5-2, 5-3, 5-4 by signal line 60 is provided to inverter cells 5-1, 5-2, 5-3, 5-4.

[0032] The inverter cells 5-1, 5-2, 5-3, and 5-4 can be selectively connected. As shown in FIG. 3A, in a first state, the inverter cells are connected in series to form a stacked inverter cell configuration. A DC voltage of, for example, 48 volts is supplied to each of the inverter cells 5-1, 5-2, 5-3, and 5-4 by the power supply unit 3, and a reference signal is applied to each of the inverter cells 5-1, 5-2, 5-3, and 5-4 via a line 60 from the common control unit 6 and transferred to the individual inverter cells 5-1, 5-2, 5-3, and 5-4 directly or via a (closed) group switch 56. Due to this series configuration, the output voltages of each of the inverter cells 5-1, 5-2, 5-3, and 5-4 are added together to form a common output voltage Vout equal to the sum of the output voltages of all the inverter cells 5-1, 5-2, 5-3, and 5-4. This is considered the first state, and the inverter cells 5-1, 5-2, 5-3, and 5-4 cooperate in such a way as to form a multilevel inverter.

[0033] FIG. 4 shows a detailed diagram of the inverter cells 5-1 and 5-2 and their cooperation. The inverter cells 5-1 and 5-2 are arranged in a cascade configuration, and both are supplied with the same DC voltage, illustratively 48 V, from the power supply unit 3, as shown at the left edge of FIG. 4. A stabilization capacitor 32 is also provided. This ensures a stable DC voltage for the two inverter cells 5-1 and 5-2. Each of the inverter cells 5-1 and 5-2 operates as a current valve and includes four power switches 51-54 arranged in an H-bridge configuration. The power switches 51-54 are power semiconductor switches, configured as, for example, IGBTs, MOSFETs, or GaN FETs. The power switches 51 and 53 are connected in series to form a first branch, and the power switches 52 and 54 are similarly connected in series to form a second branch. The center taps of the two branches are routed out and connected to both ends of the primary winding of a transformer 55. The transformer 55 includes secondary windings that serve as the outputs of the respective inverter cells 5-1 and 5-2. The two power switches 51, 53 are driven by a common signal C1.a, the signal supplied to power switch 53 being provided in inverted form. The two power switches 52, 54 of the second branch are likewise driven by a current signal C1.b, the signal supplied to power switch 52 being provided in inverted form. The signals C1.a and C1.b are generated in a manner known per se. Operation is as follows: in the case of a HIGH signal on C1.a, power switch 51 is in the ON state and power switch 53 is in the OFF state, i.e. the first power branch applies a positive potential to the upper connection of transformer 55 and ultimately to the active electrode 33. Therefore, in the case of a HIGH signal on C1.b, power switch 54 is in the ON state and power switch 52 is in the OFF state. The second power branch therefore applies a negative potential to the lower connection of transformer 55 and ultimately to the neutral electrode 34.

[0034] 3A, a first state is shown with inverter cells 5-1, 5-2, 5-3, and 5-4 connected in series in a conventional manner. A reference signal is provided by line 60 and distributed to inverter cells 5-1, 5-2, 5-3, and 5-4.

[0035] According to the present invention, there is a second selectable state in which the inverter cells 5-1, 5-2, 5-3, and 5-4 are divided into at least two groups. This is shown in FIG. 3B, which depicts two groups I and II. The groups I and II can be isolated from each other with respect to the reference signal by a first group switch 56 and with respect to the output voltage by a second group switch 57. Each group I and II generates an output voltage Vout I, Vout II that is supplied to a respective output socket 17, 17' via an electrode line. A reference signal provided by the common control unit 6 is transmitted to the inverter cells 5-1 and 5-2 of the first group I via a signal line 60, and a reference signal for the inverter cells 5-3 and 5-4 of the second group II is supplied by the common control unit 6 via a signal line 60'. The reference signals supplied by the common control unit 6 to the inverter cells 5-3, 5-4 of the second group II have the same frequency as the reference signals supplied to the inverter cells 5-1, 5-2 of the first group I, but may have a different polarity or, as shown, an opposite polarity.

[0036] In other words, the plurality of inverter cells 5-1, 5-2, 5-3, 5-4 are divided into two groups. The first group I includes inverter cells 5-1, 5-2 that generate a first output voltage Vout I, which is supplied to the first output socket 17. Similarly, the second group II includes inverter cells 5-3, 5-4 that generate a second output voltage Vout II, which is supplied to the second output socket 17'. This allows each inverter cell to supply its own output voltage to either of the output sockets 17, 17' and their respective electrosurgical instruments 19, 19', which can be used simultaneously and independently of each other (dual activation). The operation of the inverter cells 5-1, 5-2 of the first group I is controlled by a reference signal carried via line 60, and the operation of the inverter cells 5-3, 5-4 of the second group II is controlled by a reference signal carried via line 60', which has the same frequency as the reference signal carried via line 60.

[0037] The inverter units 4 and inverter cells 5-1, 5-2, 5-3, 5-4 are controlled by a common control unit 6. The common control unit 6 communicates with the master controller 2 and operates according to instructions and commands issued by the master controller 2. The common control unit 6 comprises a reference signal generator 61 configured to generate a reference signal for driving the inverter units 4. The reference signal determines, among other things, the frequency, phase, and usually also the amplitude, of the high frequency AC voltage generated by the inverter units and their inverter cells 5-1, 5-2, 5-3, 5-4.

[0038] Furthermore, the common control unit 6 comprises a synchronization unit 62 and a phase-shift unit 63. The synchronization unit 62 is configured to synchronize the frequency of the reference signal 60' supplied to the second group II of inverter cells 5-3 and 5-4 to the frequency of the reference signal 60 supplied to the first group I of inverter cells 5-1 and 5-2. This ensures that the groups I and II of inverter cells 5-1, 5-2, 5-3 and 5-4 are driven at the same frequency so that no frequency difference is realized, and as a result, no beat frequency occurs. To verify this condition, a beat frequency monitor 66 is provided that is configured to determine the beat frequency and interacts with the synchronization unit 62, e.g., to ensure synchronism, particularly frequency synchronism.

[0039] Similarly, the phase shift unit 63 adjusts the phase of one of the reference signals 60, 60' so that the reference signals 60, 60' have a predetermined phase shift. The phase shift can be preselected either by a user and / or by the master controller 2. In many cases, this predetermined phase shift will be zero so that the reference signals 60, 60' not only have the same frequency but also the same phase. Furthermore, it may be desirable to invert the reference signal 60' relative to the reference signal 60. For this purpose, a polarity inverter 65 is provided in the common control unit 6, which preferably inverts the reference signals 60' of the second group II.

[0040] The common control unit 6 further includes a state switch 64, which is activated when the inverter changes from a first state, in which all inverter cells 5-1, 5-2, 5-3, and 5-4 operate uniformly in a conventional manner, to a second state, in which the inverter cells 5-1, 5-2, 5-3, and 5-4 are divided into groups. Upon entering the second state, the state switch 64 operates the group switches 56 and 57 to isolate the connections between the groups of inverter cells 5-1, 5-2, 5-3, and 5-4, thereby allowing groups I and II to operate independently. The operation of the group switch 56 is essential to enable independent control of both groups I and II. The operation of the second group switch 57 is optional, depending on whether the electrodes of both groups I and II are galvanically isolated from each other or whether they share a common electrode, typically a shared neutral electrode as shown by the dashed-dotted line in FIG. 3B .

[0041] Refer to Figures 5A and 5B, which illustrate the equivalent circuit diagram and currents of a monopolar electrosurgical instrument. This relates to the operation of electrosurgical generator 1 with inverter unit 4 in the second state configuration. Inverter cells 5-1, 5-2, 5-3, and 5-4 are divided into two groups I and II. The output voltage provided by group I, which supplies electrosurgical instrument 19, is symbolized as a voltage source designated by the reference character "I." The output voltage provided by group II, which supplies electrosurgical instrument 19', is symbolized as a voltage source designated by the reference character "II." The body tissue surrounding electrosurgical instruments 19 and 19' is symbolized by impedances Zinstr1 and Zinstr2, respectively. Additionally, both monopolar electrosurgical instruments share a common neutral electrode, which is symbolized by the resistance Rcom of the common neutral electrode path.

[0042] In Figure 5B, the oscillation curve relates to the prior art. It shows the current flowing through the electrosurgical instrument 19 (through Zinstr1). As occurs in the prior art, the voltage sources of both electrosurgical instruments 19, 19' have a slight frequency difference, approximately 3% in the illustrated case. The fluctuating amplitude of the oscillation curve represents a resulting beat frequency, indicating an undesirable modulation of the current flowing through the electrosurgical instrument 19. This adversely affects reliable operation of the electrosurgical instrument 19. By synchronizing the frequencies of the output voltages of Groups I and II in accordance with the present invention and inverting the reference signal of one of the groups by polarity inverter 65, the frequency difference is eliminated, and therefore the beat frequency does not occur. Furthermore, this inversion effectively cancels the currents through both electrosurgical instruments 19, 19' so that the current IRcom flowing through the common electrode, symbolized by the impedance Rcom, is always zero (the straight line at 0 mA in Figure 5B). This allows for much smoother operation of both electrosurgical instruments 19, 19' and further neutralizes the current flowing through the common body electrode, further reducing current distortion on the patient's body.

[0043] Reference is now made to Figures 6A and 6B, which illustrate the equivalent circuit diagram and currents of a bipolar electrosurgical instrument. Similar to the scenario in Figures 5A and 5B, this relates to the operation of electrosurgical generator 1 with inverter unit 4 in a second state configuration. Inverter cells 5-1, 5-2, 5-3, and 5-4 are divided into two groups I and II, with the output voltage provided by group I supplying electrosurgical instrument 19 symbolized as a voltage source designated by reference character "I," and the output voltage provided by group II supplying electrosurgical instrument 19' symbolized as a voltage source designated by reference character "II." The body tissue surrounding electrosurgical instruments 19 and 19' are symbolized by impedances Zinstr1 and Zinstr2, respectively. Cross currents can flow through the patient's body between the locations of both electrosurgical instruments 19 and 19', with the respective impedances symbolized by impedance Rbody in Figure 6A.

[0044] As in Figure 5B, in Figure 6B, the large oscillation curve relates to the prior art. This indicates unwanted current flowing through the patient's body at the upper Rbody impedance. Again, as occurs in the prior art, the voltage sources of both electrosurgical instruments 19, 19' have a slight frequency difference—approximately 3% in the illustrated case. The large oscillation curve with its fluctuating amplitude represents a resulting beat frequency indicating that the patient's body experiences significant cross current between the two electrosurgical instruments 19, 19'. Even worse, this unwanted cross current is modulated by the beat frequency. By synchronizing both groups I and II to the exact same frequency according to the present invention, there is no frequency difference, no modulation occurs, and ultimately, the beat frequency becomes nonexistent. This has the additional positive effect of substantially reducing the magnitude of the cross current flowing through the patient's body; in addition to being lower, the cross current is constant and no longer modulates. As a result, the strain affecting the patient's body is significantly reduced.

[0045] Note that the amplitude of the remaining cross current may be affected. For this purpose, a cross current monitor 67 is provided, connected to the sensor device 38, 38' of either output socket 17, 17'. Using the measurements, the cross current monitor 67 is configured to determine the cross current flowing through the patient's body. The cross current monitor 67 cooperates with an automatic polarity switch 69 in the common control unit 6. By switching polarity using the polarity inverter 65 and comparing the cross current flowing with and without the polarity inverter 65 engaged, it is determined at which polarity the cross current results remain low. The automatic polarity switch 69 therefore sets the polarity reversal to obtain a low cross current. This may vary dynamically depending on the actual location where the electrosurgical instrument 19 is used, and conditions may change frequently and rapidly depending on Rbody fluctuations. The automatic polarity switch 69 automatically tracks this, thus providing a valuable boost to the utility of the dual-activated electrosurgical instrument. [Explanation of symbols]

[0046] 1 electrosurgical generator 2 Master Controller 3 Power Supply Unit 4 Inverter Unit 5-1~5-4 Inverter cells 6 Common Control Unit 11. Housing 12 plugs 13 Power cable 14 User Interface 15 Display 16,16' knob 17,17',17'' output socket 18,18' plug 19,19' Electrosurgical Instruments 30 DC bus 32 Stabilizing capacitor 33,33' active electrode 34,34' Neutral electrode 36,36' filter 37,37' Step-up transformer 38,38' Sensor device 51~54 Power switch 55 Transformer 56 First Group Switch 57 Second Group Switch 60,60' Reference signal (signal line) 61 Reference Signal Generator 62 Synchronous Unit 63 Phase Shift Unit 64 Status Switch 65 Polarity Inverter 66 Beat Frequency Monitor 67 Cross-current monitor 69 Automatic polarity switch I. First Group II. Second Group

Claims

1. 1. An electrosurgical generator configured to output a high frequency alternating current voltage to an electrosurgical instrument, comprising: an inverter unit for generating a high frequency AC voltage to be supplied to at least two output sockets for connection of said electrosurgical instruments; the inverter unit is configured to simultaneously activate electrosurgical instruments connected to the at least two output sockets, respectively, and includes a plurality of inverter cells cooperating with one another; the plurality of inverter cells are cascaded in a first state and divided into at least two groups in a second state; An electrosurgical generator, wherein each of the at least two groups is assigned to one of the at least two output sockets, supplies its generated high frequency AC voltage as an output voltage to the assigned output socket via an electrode wire, and is commonly controlled by a synchronized reference signal generated by a common control unit.

2. The electrosurgical generator according to claim 1 , wherein the inverter unit is a multi-level inverter.

3. The electrosurgical generator of claim 1 , wherein the reference signals are synchronized so that the output voltages have the same frequency.

4. The electrosurgical generator according to claim 3, wherein the output voltage of one of the at least two groups is synchronized in phase with a predetermined phase shift to the output voltage of another group.

5. The electrosurgical generator according to claim 4, wherein the predetermined phase shift is zero so that the output voltages have the same phase angle.

6. The electrosurgical generator according to claim 4 , wherein the output voltage of one of the at least two groups is inverted relative to the output voltage of another group.

7. The electrosurgical generator according to claim 1 , wherein the at least two groups share a common neutral electrode that is one of the electrode wires.

8. An electrosurgical generator according to claim 7, wherein the output socket is configured for a monopolar electrosurgical instrument.

9. each of the at least two groups having an active electrode and an inert electrode; The electrosurgical generator according to claim 1 , wherein the active electrode and the indifferent electrode are not shared between the at least two groups.

10. An electrosurgical generator according to claim 9, wherein the output socket is configured for a bipolar electrosurgical instrument.

11. An electrosurgical generator according to claim 9, wherein the polarity of the output voltage of one of the at least two groups is selectively changed by a polarity inverter.

12. An electrosurgical generator according to claim 11, further comprising a current monitor configured to determine cross current between the output sockets.

13. The electrosurgical generator according to claim 12, wherein at least one of the at least two groups is provided with an automatic polarity switcher configured to cooperate with the current monitor to identify a polarity having a minimum cross current.

14. 14. The electrosurgical generator according to claim 13, wherein the automatic polarity switcher cooperates with the current monitor to (i) determine the cross current in a first polarity state, (ii) then switch the polarity to a second polarity state and determine the cross current in the second polarity state, (iii) compare the cross currents in the first and second polarity states, (iv) determine which polarity state has a low cross current, and (v) select the polarity having the low cross current.

15. The electrosurgical generator according to claim 1 , further comprising a beat frequency monitor configured to determine a beat frequency between the outputted high frequency alternating voltages of the at least two output sockets.

16. The electrosurgical generator according to claim 15, wherein the beat frequency monitor cooperates with a synchronization unit to ensure frequency and phase synchronism between the at least two groups.

17. An electrosurgical generator according to claim 7, further comprising a switching device configured to selectively change the neutral electrode between a shared state and a non-shared state.

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