Generator with plasma length display

Abstract

The generator (10) according to the invention contains at least one converter module with a transformer, the secondary winding of which is electrically connected to the electrode (17) of an instrument (12) and to a counter electrode (14). The primary winding of the transformer is connected to operating voltage on the one hand and to ground on the other hand via an electronic switch. The switch blocks periodically, whereby voltage pulses are generated in the secondary winding, which feed a spark or other plasma for the medical treatment of a patient. A voltage detector is used to display the plasma length. This detects the voltage occurring at the primary winding and displays it via an indicator device (24). The invention is based on the idea that the voltage occurring at the primary winding, in particular the peak voltage, characterizes the length of the generated plasma (16).The inventor has found that factors other than the plasma length are of minor importance in influencing the voltage measured at the primary coil.

Description

[0001] The invention relates to an electrosurgical generator designed to carry out HF surgical applications.

[0002] Electrosurgical generators are generally known from the prior art. For example, US 2018 / 0243558 A1 discloses a generator consisting of individual pulse generators connected in parallel on the output side. This generator can be used to generate targeted voltage pulses for electrosurgical treatment of a patient.

[0003] US 2011 / 0060329 A1 further discloses an electrosurgical generator for generating a DC voltage for treatment. For this purpose, the generator comprises a flyback converter, which charges an output capacitor, on which a DC voltage is generated. The generator can comprise several such blocks to power multiple loads.

[0004] EP 4 147 656 A1 discloses a generator comprising several generator modules connected in series on the output side and operating according to the flyback converter principle. Each generator module contains an externally controlled switch and a transformer, with the primary winding of the transformer connected in series with the switch. The secondary windings of the various generator modules are connected in series with one another. The switch is externally controlled in a control circuit so that it can specifically build up a current in the primary winding of the transformer and then abruptly switch it off. Induction at the transformer creates a large voltage peak in the secondary winding and a smaller voltage peak in the primary winding corresponding to the transformation ratio. To prevent the switch from being destroyed by excessive primary voltage peaks, a protective capacitor is connected in parallel with the switch.

[0005] Further prior art is provided by US 2015 / 0133912 A1, US 4,878,493 and WO 2011 / 146498 A2.

[0006] At least some of the aforementioned electrosurgical generators are suitable for supplying voltage to an instrument having an electrode for treating biological tissue. For treatment, an electric spark or plasma can be maintained between the tissue and the electrode, the length of which influences the physiological effect. The electrode can be arranged in a gas stream, in particular an inert gas stream, for example, an argon stream, which sweeps along the electrode and is directed toward the biological tissue. Such instruments are referred to as argon plasma probes or argon plasma instruments.

[0007] An example of such an argon plasma instrument is known, for example, from EP 1 684 653 B1. This instrument comprises a tube-like or hose-like base body with a channel for gas and plasma guidance opening at the distal end. An electrode for ionizing the gas jet is arranged in the channel, so that the instrument generates a plasma jet that exits the instrument in the distal direction.

[0008] Further instruments are known from DE 100 30 111 A1 or EP 1 293 170 A1.

[0009] When treating biological tissue, the practitioner's view of the treatment site may be limited. This sometimes makes it difficult for the practitioner to estimate the length of the generated plasma. However, the length of the generated plasma can have a significant impact on the treatment outcome.

[0010] This leads to the object underlying the invention of creating a possibility to convey the length of the generated plasma to the practitioner even when the view of the treatment site and the generated plasma is restricted.

[0011] This object is achieved with the generator according to claim 1:

[0012] The electrosurgical generator according to the invention is designed to power HF surgical instruments, in particular instruments that generate a plasma jet. For this purpose, the generator has at least one converter module, which is connected to a DC voltage on the input side in order to be supplied with electrical power from this. The converter module has an output configured to deliver a sequence of high-voltage pulses. The pulse repetition frequency can exceed a minimum frequency of 100 kHz, so that the pulse sequence forms a high-frequency high voltage. In particular, a non-sinusoidal high voltage can be generated.

[0013] The converter module comprises a transformer with a primary winding and a secondary winding. While the secondary winding forms the output of the converter module, the primary winding is connected to an externally controlled electronic switch. This switch has a control electrode connected to a control circuit and a control path that connects one terminal of the primary winding to ground (controlled). The other terminal of the primary winding is connected to the operating voltage.

[0014] A connection point is formed between the control path and the end of the primary winding connected to the control path, to which a voltage detector is connected. This voltage detector is configured to detect the voltage occurring at this connection point. The voltage detector also has an indicator device configured to generate a signal dependent on the voltage detected by the voltage detector. This signal is a signal perceptible to the practitioner, for example, a visual, acoustic, or even a haptic signal. Combinations of such signals are also possible.

[0015] The voltage detected by the voltage detector depends on the length of the generated plasma. This plasma can form, for example, between the electrode of an instrument connected to the generator output and biological tissue that is also connected to the generator output via a neutral electrode. This applies to monopolar instruments. However, bipolar instruments with two electrodes connected to the generator, between which the plasma is formed, are also possible.

[0016] Based on the signal provided to them, the practitioner can draw conclusions about the length of the plasma present at the instrument and adjust their actions accordingly. For example, they can avoid generating plasma lengths that are too long or too short, even leading to direct contact between the instrument's electrode and the tissue. The invention helps the practitioner control the appropriate distance between the instrument or electrode and the tissue and maintain a suitable distance during treatment.

[0017] The voltage detector can be a peak voltage detector that indicates the maximum voltage occurring at the connection point. This can also be implemented as a sample-and-hold circuit, in which the voltage measurement performed by the voltage detector is synchronized with the switching of the externally controlled switch. For this purpose, the control circuit controlling the switch can be connected to the voltage detector. The voltage detector can then receive control pulses from the control circuit.

[0018] If the voltage detector is a peak voltage detector, it typically contains a storage capacitor connected to the connection point via a current path to charge to the peak voltage present there. If the voltage detector is a sample-and-hold circuit, a discharge current path can be connected in parallel with the storage capacitor. This can include a controlled discharge switch controlled by the control circuit to discharge the storage capacitor shortly before the time at which the controlled switch of the converter module is blocked, thus reaching a new peak voltage.

[0019] The generator can comprise several converter modules of the described design. These converter modules are preferably supplied with energy or power from a DC voltage in parallel. On the output side, the converter modules are preferably connected in series. Each converter module can "fire" individually, i.e., emit a high-voltage pulse at its output when its controlled switch is briefly blocked. A "firing sequence" is then a sequence of high-voltage pulses in which each converter module participating in the firing sequence has fired one or more times. The firing sequence corresponds to a sequence of control signals that the control circuit generates and transmits to the switches of the converter modules. The control circuit can be configured to periodically repeat the sequence of control signals as often as required to generate an RF output voltage. Accordingly, the RF output voltage is generated by continuously repeating the firing sequence.

[0020] The control circuit is preferably configured to block the controlled switches of the converter modules individually or in groups during a firing sequence, with the other switches of the other converter modules then preferably being kept open. This allows the high-voltage outputs of the converter modules not currently firing to be open to the high-voltage pulses of the firing converter modules. A converter module fires when its controlled switch is blocked (preferably briefly), thus generating a high-voltage output pulse.

[0021] Each of these converter modules can have a voltage detector of the type described. However, it has been shown that it may be sufficient to connect a single converter module or only some of the converter modules to the voltage detector mentioned.

[0022] Further details of embodiments of the invention are evident from the dependent claims as well as the description and the accompanying drawings. In these: Figure 1 the generator according to the invention and an instrument connected to it, in schematic representation, Figure 1a the distal end of an instrument during operation in a longitudinal section, Figure 2 a generator with a single converter module and plasma length display in a schematic diagram, Figure 3 a generator with several converter modules and a voltage detector, in schematic diagram, Figure 4 a modified generator according to Figure 3 , in principle representation, Figures 5 to 8 Circuit diagrams and voltages of the generator according to Figures 2 to 4 , Figure 9 a relationship between the voltage detected by the voltage detector and the plasma length, Figure 10Examples of firing sequences of the converter modules and the operation of the voltage detector.

[0023] In Figure 1 Illustrated is a device G with a generator 10 according to the invention, to which an instrument 12 for treating biological tissue 13 is connected via a line 11. The biological tissue 13 is connected to the generator 10 via a neutral electrode 14 and a line 15. Figure 1 thus illustrates a monopolar instrument in which current flows from the instrument 12 to the tissue 13. In principle, however, the invention is also applicable to bipolar or multipolar instruments that act on biological tissue by means of a plasma 16. In Figure 1 the plasma 16 is illustrated by jagged arrows.

[0024] The instrument 12 has at least one electrode 17 for plasma generation, which is electrically connected to the generator 10 via the line 11. In Figure 1The instrument 12 is illustrated as a handle with an electrode 17 protruding therefrom. Such instruments are suitable for open surgery. The electrode 17 can protrude from the handle 18 and be designed like a needle or scalpel. However, it is also possible to arrange the electrode 17 in a channel 19 that extends through the instrument 12 and is connected at the proximal end 20 to the supply device G, which then has a corresponding gas supply in addition to the generator 10.

[0025] At the distal end 21 ( Figure 1a ), the gas introduced into the channel 19 by the device G can flow out. It can be ionized via the electrode 17, so that an outflowing plasma stream 16 is formed, which is again illustrated by jagged arrows. The instrument 12 can be positioned as shown in Figure 1As shown, it can be designed both as an instrument intended for open surgery, as a laparoscopic instrument, and as a probe that is guided to the surgical site, for example, through the working channel of an endoscope. What all of these applications have in common, however, is that the practitioner does not always have an unrestricted view of the plasma stream 16 and its length.

[0026] The device G has, as Figure 1 illustrated, both a display device 22 and operating elements 23, for example keys, buttons and the like. In addition, the device G has an indicator device 24, which serves to display the length of the plasma stream 16. The indicator device 24 is in Figure 1as an optical indicator device that displays a light bar symbolizing the length of the plasma stream 16. Furthermore, the light bar may have colored fields at at least one of its ends to signal a plasma stream 16 that is too long and / or too short.

[0027] The indicator device 24 can be designed as an optical indicator device and, if necessary, also integrated into the display device 22. Furthermore, it is possible to additionally or alternatively provide the indicator device 24 with acoustic display means. Additionally or alternatively, the indicator device 24 can be designed to generate haptically perceptible signals, such as vibrations perceptible in the handle 18 or elsewhere.

[0028] Figure 2illustrates a simplified representation of part of the electrical circuit of generator 10. The previously introduced reference numerals will continue to be used below with the same meaning.

[0029] The electrosurgical generator 10 comprises a converter module 25, which includes an electrical circuit designed in the manner of a flyback converter. This is formed by an externally controlled electronic switch 26, for example in the form of a field-effect transistor, a bipolar transistor, an insulated-gate bipolar transistor, or another electronic switch, which is connected in series with a primary winding 27 of a transformer 28. A first end of the primary winding 27 is connected to a positive operating voltage U b , while the other end of the primary winding 27 is connected to a connection point 29. The externally controlled electronic switch 26 is connected to this connection point 29 at one end (drain or collector), while the other end of its control path (source or emitter) is connected to ground potential M.

[0030] The externally controlled electronic switch 26 also has a control electrode 30 which is connected to a control circuit 31 in order to release or block the control path of the electronic switch 26 in a controlled manner.

[0031] The transformer 28 also has a secondary winding 32, one end of which is optionally connected to the electrode 17 of the instrument 12 via a coupling capacitor 33. The other end of the secondary winding is optionally connected via another coupling capacitor 34 to the neutral electrode 14, which is to be attached to the patient and thus to the biological tissue 13. The secondary winding 32 or, if present, the electrodes of the coupling capacitors 33, 34 facing away from the secondary winding form the output of the converter module 25 and thus of the generator 10.

[0032] A protective capacitor 35 or other protective circuitry can be connected in parallel with the electronic switch 26. The protective capacitor 35 has one terminal connected to connection point 29 and its other terminal connected to ground. It serves to limit the voltage across the switch 26.

[0033] A voltage detector 36 is connected to the connection point 29 and is designed to detect the voltage UP occurring at the connection point 29 and thus at the switch 26 (as well as the protective capacitor 35). The voltage detector 36 includes the indicator device 24, which serves to generate a signal that is dependent on the detected voltage UP ( Figure 6 ) and indicates its magnitude. The indicator device 24 can be arranged, for example, on the device G or generator 10 or on the instrument 12 or at a separate location.

[0034] Preferably, the voltage detector 36 is designed as an integrating detector or a peak value detector. It has a storage capacitor C, which is connected to the connection point 29 via a charging circuit 37. In the simplest case, the position circuit 37 is a diode polarized in the forward direction with respect to the voltage U p occurring at the connection point 29. Preferably, a particularly low-capacitance diode is used. To reduce the parasitic capacitance of the charging circuit 37, several diodes can be connected in series.

[0035] An evaluation circuit 38 is connected in parallel to the storage capacitor C, which on the one hand indicates the voltage of the capacitor C by means of the indicator device 24 and on the other hand is designed to periodically discharge the storage capacitor C.

[0036] The generator described so far operates as follows: To treat tissue 13, electrode 17 is brought close to tissue 13. Control circuit 31 then closes and opens switch 26 in rapid succession, thus firing converter module 25. If switch 26 is conductive, a current flows from the (e.g., positive) operating voltage U b through primary winding 27 from the coil start, marked by a dot, to the coil end, and thus via connection point 29 and conductive switch 26 to ground potential M. Whenever control circuit 31 applies a blocking pulse to control electrode 30, switch 36 is blocked, preventing further current flow to ground. The current flow now commutates to secondary winding 32, where the current continues to flow from the coil start, marked by the dot, to the coil end (and thus to coupling capacitor 33) and via this to electrode 17.

[0037] The sparking to the tissue 13 as a result of the generated high-voltage pulses creates the plasma 16, which can burn in air, steam, or a specially induced gas, such as argon. The voltage building up between the electrode 17 and the tissue 13 or the neutral electrode 14 is a measure of the length of the plasma 16. The voltage present between the electrode 17 and the neutral electrode 14 is also present at the secondary winding 32. Due to the transformation factor of the transformer 28, the corresponding voltage U p is also present at the primary winding 27 and, as a corresponding voltage pulse, at the connection point 27. For explanation, reference is made to the diagrams according to Figures 5 and 6 referred to:

[0038] In Figure 5Switch 26 is conductive during the time period t1. The conductive state is marked on the ordinate with the capital letter L. At the end of the time period t1, switch 26 is blocked. The blocking phase begins, which is Figure 5 is characterized by the time period t2. The non-conductive state is characterized on the ordinate by the letter N. At the beginning of the blocking phase t2, the described voltage pulse U p is generated at the primary winding 27 and, correspondingly, also at the secondary winding 32. This voltage pulse U p is in Figure 6 in three different sizes U p1 , U p2 , U p3 , which corresponds to three different plasma lengths of the plasma 16. It can be seen that the longer the plasma 16 is, the larger the voltage pulse U p is.

[0039] Figure 7illustrates the voltage U on the storage capacitor C. During the voltage pulse U p , current flows through the charging circuit 37 to the storage capacitor C, charging it to a corresponding voltage U1, U2, or U3. The larger the voltage pulse U p , the greater the voltage U present on the storage capacitor C.

[0040] The storage capacitor C can be discharged from time to time as required. For example, it can be discharged before, during or after the switch 26 is switched on again, which is Figure 5 takes place in the conduction phase t3. Figure 8 illustrates such a discharge pulse D1.

[0041] The indicator device 24 is designed to generate a signal corresponding to the voltage U1, U2 or U3, for example by a light bar displayed by it changing its length in steps or continuously according to the voltage U on the storage capacitor C.

[0042] Figure 3 illustrates a further developed form of the generator according to Figure 2 , whereby the above description applies while retaining the reference symbols already introduced and additionally taking into account the following explanation:

[0043] The generator after Figure 3 has a plurality of converter modules 25, 25a, 25b, 25c, wherein the converter modules 25a, 25b, 25c are preferably identical in construction to the converter module 25 and the previous description applies accordingly with the addition of a respective letter indices.

[0044] The charging circuit 37 is connected at least to the connection point 29 and initially leads via a chain circuit of forward-biased diodes to a circuit point E. From this circuit point E, the current path preferably leads via a resistor 38 and a parallel-connected capacitor 39 to the storage capacitor C. The indicator device 24 is connected to this storage capacitor C.

[0045] For occasional, regular, or as-needed discharge of the storage capacitor C, a discharge circuit 42 is provided with a discharge current path 43 in which a discharge switch 40 is arranged. The discharge switch 40 has a control path connected in parallel with the storage capacitor C. Its control electrode 41 is connected to the control circuit 31, which now controls not only all switches 26, 26a, 26b, 26c, but also the discharge switch 40. In this case, the Figure 8The pulse D1 illustrated above represents the time period during which the discharge switch 40 is enabled, ie, conducts. This allows the charge to flow from the storage capacitor C, causing the voltage U1, U2, or U3 to collapse, ie, to fall to near zero.

[0046] In many cases, it is sufficient if the charging circuit 37 merely connects the connection point 29 to the circuit point E. However, it may be useful to also connect one or more of the converter modules 25a, 25b, 25c with corresponding charging circuits 27a, 27b, 27c to the voltage point E.

[0047] The control circuit 31 can be configured to activate and deactivate the converter modules 26, 26a, 26b, 26c in a coordinated manner, ie to open and close their respective switches 26, 26a, 26b, 26c. For this purpose, the individual switches 26, 26a, 26b, 26c can be individually switched from their conducting state briefly into the blocking phase T2 according to Figure 5to generate, i.e., fire, their respective secondary windings 32, 32a, 32b, or 32c. Preferably, the switches of those converter modules 25, 25a, 25b, 25c that are not firing are conductive. This allows the high-voltage pulse emitted by the respective firing converter module 25, 25a, 25b, 25c to penetrate the then low-resistance secondary windings of the non-firing converter modules, so that the high-voltage pulse can flow through the series-connected secondary windings 32, 32a, 32b, 32c.

[0048] Figure 10illustrates a firing sequence F based on the voltage U 17 at the electrode 17. The converter modules 25 and 25a fire simultaneously, followed by the converter modules 25b, 25c. The voltage detector 36 connected to the converter module 25 detects the voltage U p, whereby the capacitor C is charged accordingly. The charge remains until it is extinguished again by the control circuit 31 activating the discharge switch 40. It can do this at the end of the firing sequence F if only the voltage U p at one of the converter modules is monitored. If several or all of the converter modules 25, 25a, 25b, 25c are connected to the voltage detector 36, the capacitor can also be discharged before the next converter module fires.

[0049] Typically, the control circuit 31 causes the converter modules 25, 25a, 25b, 25c to fire individually or in groups according to a predetermined pattern. This can produce high-voltage pulses of the same or different magnitude, such as Figure 10 If the discharge of the storage capacitor C always occurs after a firing sequence has been completed, a voltage builds up on the storage capacitor C that is determined by the largest of the high-voltage pulses generated in the firing sequence F. This voltage indicates the arc length or plasma length, which is displayed by indicator 24.

[0050] Figure 9illustrates the relationship between the voltage U c present on the storage capacitor C and the arc length l. Different arc lengths l 1 , l 2 result in different voltages U1, U2, whereby the relationship is largely linear, at least within a limited but relatively large range. Regardless of the linearity, the voltage U c is a measure of the arc length l.

[0051] A further modified embodiment of the generator according to the invention is shown in Figure 4 The reference numerals already introduced also apply to this embodiment, because the description relating to it applies accordingly. The difference between the embodiment according to Figure 4 and the embodiment according to Figure 3 lies (solely) in the polarity of the secondary windings 32, 32a, 32b, 32c. While in the embodiment according to Figure 3all secondary windings 32, 32a, 32b, 32b, 32c are polarized the same, with the winding beginnings marked by a dot being oriented towards the neutral electrode 14, in the embodiment according to Figure 4 Different polarities are present. The secondary windings 32, 32a are oriented with their winding beginnings toward the neutral electrode 14, while the secondary windings 32b, 32c are oriented with their winding beginnings toward the electrode 17. However, it should be noted that other groupings and polarities can also be used.

[0052] In the embodiment according to Figure 4 When fired, the converter modules 25, 25a generate positive voltage pulses at the electrode 17, while the converter modules 25b, 25c generate negative voltage pulses at the electrode 17. (This applies to a positive operating voltage U b ; the opposite is true for a negative operating voltage U b .)

[0053] By interconnecting converter modules 25, 25a, 25b, and 25c with different polarities, both symmetrical and asymmetrical RF output voltage sequences can be generated. Even with symmetrical RF pulse sequences containing both positive and negative voltage peaks, the plasma length can be displayed, as described above, by detecting the voltage U p at the appropriate connection points 29 and / or 29a, 29b, and 29c.

[0054] The generator 10 according to the invention contains at least one converter module with a transformer 28, the secondary winding 32 of which is electrically connected to the electrode 17 of an instrument 12 and to a counter electrode 14. The primary winding 27 of the transformer 28 is connected to the operating voltage U b on the one hand and to ground M on the other hand via an electronic switch 26. The switch 26 blocks periodically, whereby voltage pulses are generated in the secondary winding 32, which feed a spark or other plasma for the medical treatment of a patient. A voltage detector 36 is used to display the plasma length. This voltage detector detects the voltage U p occurring at the primary winding 27 and displays it via an indicator device 24. The invention is based on the idea that the voltage U p occurring at the primary winding 27, in particular the peak voltage, characterizes the length of the generated plasma 16.The inventor has found that factors other than the plasma length are of minor importance in influencing the voltage U p measured at the primary coil 27. Reference symbol:

[0055] 10Generator GDevice 11Lead 12Instrument 13Biological tissue 14Neutral electrode 15Lead 16Plasma, plasma current 17Electrode 18Handle 19Channel 20Proximal end 21Distal end 22Display device 23Control elements 24Indicator device 25Converter module 26Externally controlled electronic switch 27Primary winding of the transformer 28 28Transformer U b Operating voltage 29Connection point MGround potential FFire sequence 30Control electrode 31Control circuit 32Secondary winding 33, 34Coupling capacitors 35Protection capacitor 36Voltage detector CStorage capacitor U cVoltage on the storage capacitor C 37Charging circuit t1, t3Conducting phases of the switch 26 t2 U p ,Blocking phase of the switch 26 U p1 - U p3 U,Voltage pulses U1 - U3Voltage on the storage capacitor l, l 1 , l 2 Arc length ESwitch point 38Resistance 39Capacitor 40Discharge switch 41Control electrode D, D1Discharge pulse 42Discharge circuit 43Discharge current path

Claims

1. Electrosurgical generator (10), in particular for HF-surgical applications, comprising a converter module (25) which has an externally controlled switch (26) connected to a control circuit (31) and a transformer (28), the primary winding (27) of which is connected in series with the switch (26) and the secondary winding (32) of which is connected to an electrode (17) and a counter electrode (14), wherein a patient (13) to be treated can be placed between the electrode (17) and the counter electrode (14), with a voltage detector (36) which is connected to the switch (26) and is designed to measure the voltage (U p ) and which has an indicator device (24) which is designed to indicate a voltage (U p ) dependent signal.

2. Generator according to claim 1, characterized in thatthe externally controlled switch (26) is connected at one end to a reference potential (M) and at another end to a connection point (29) which is connected to one end of the primary winding (27), the voltage detector (36) being connected to the connection point (29).

3. Generator according to one of the preceding claims, characterized in that the voltage detector (36) is a peak voltage detector.

4. Generator according to one of the preceding claims, characterized in that the voltage detector (36) is a sample-and-hold circuit.

5. Generator according to one of the preceding claims, characterized in that the voltage detector (36) contains a storage capacitor (C) which is connected to the switch (26) via a charging circuit (37).

6. Generator according to claim 5, characterized in that the charging circuit (37) is formed by at least one, preferably several, diodes connected in series with one another.

7. Generator according to claim 5 or 6, characterized in that the storage capacitor (C) is assigned a discharge circuit (42) which has a controllable discharge current path (43) which is connected in parallel to the storage capacitor (C).

8. Generator according to claim 7, characterized in that the discharge circuit (42) is connected to the control circuit (31) so that its discharge current path (43) can be alternately switched back and forth between non-conductive and conductive states by the control circuit (31).

9. Generator according to claim 8, characterized in that the control circuit (31) is designed to alternately open and block the externally controlled switch (26), and is further designed to also block the discharge current path (43) when the switch (26) is blocked.

10. Generator according to claim 9, characterized in thatthe control circuit (31) is arranged to temporarily open the discharge current path (42) before blocking the switch (26).

11. Generator according to one of the preceding claims, characterized in that in addition to the converter module (25), at least one further converter module (25a) is provided, wherein the secondary windings (32, 32a) of the converter modules (25, 25a) are connected in series.

12. Generator according to claim 11, characterized in that the converter modules (25, 25a) are of identical construction.

13. Generator according to claim 11 or 12, characterized in that the secondary windings (32, 32a) of at least some of the converter modules (25, 25a) are connected in series in the same direction.

14. Generator according to one of claims 11 to 13, characterized in that the secondary windings (32a, 32b) of at least some of the converter modules (25a, 25b) are connected in series in opposite directions.

15. Generator according to one of claims 11 to 14, characterized in thatthe voltage detector (36) is connected to only one of the converter modules (25, 25a, 25b, 25c).