Transformer based ac / ac conversion cells for modular ac / dc, dc / ac or dc / dc converter

Abstract

The present invention relates to an electric converter (1") comprising: (i) a plurality of primary windings (3-R, 3-S, 3-T); and (ii) a plurality of secondary windings (4-a...4-n, 5-a...5-n, 6-a...6-n) magnetically linked to said plurality of primary windings (3-R, 3-S, 3-T); and a plurality of groups of reconfigurable connection modules connected to three terminals (R', S', T) of said electric converter (1"), said plurality of groups of reconfigurable connection modules are interconnected, wherein each group in said plurality of reconfigurable connection module groups comprising respective sets of reconfigurable connection modules electrically coupled to said sets of secondary windings; and in which each reconfigurable connection module includes a plurality of electronic switches configured to establish, in successive instants: a direct connection, a bypass connection, and a reverse connection wherein the voltage supplied to the input of the respective reconfigurable connection module is transferred to its output with inverted polarity.

Description

[0001] TRANSFORMER BASED AC / AC CONVERSION CELLS FOR MODULAR AC / DC, DC / AC OR DC / DC CONVERTER

[0002] This invention relates to an electric converter, such as a direct-alternating converter (DC / AC), an alternating-direct converter (AC / DC), or a direct-direct converter (DC / DC) equipped with three DC terminals.

[0003] The invention also relates to a system comprising an electric converter and a corresponding control device that allows to control the cyclic inversion sequence of the polarity of the three terminals of the electric converter.

[0004] Lastly, the invention pertains to a network of control devices to control a plurality of electric converters.

[0005] Background

[0006] The ongoing decarbonization process is leading to an increased use of renewable energy sources, such as of the wind and photovoltaic type, for electricity production. In some operational scenarios, the use of renewable energy sources has caused instability in frequency and / or voltage of transmission and distribution networks.

[0007] One solution to this problem may be to integrate direct -current transmission and distribution networks alongside existing alternating-current networks, as direct- current networks are less prone to stability issues.

[0008] These direct-current transmission and distribution networks connect to corresponding existing alternating-current networks using AC / DC converters to exchange power in one direction and DC / AC converters to exchange power in the opposite direction; networks with different DC voltage levels are interconnected using DC / DC converters.

[0009] Patent IT 102021000010934 describes AC / DC converters, DC / AC converters, and direct-current DC / DC converters that are more cost-effective and compact compared to traditional converters used to power such transmission and distribution networks.

[0010] The control of such electric converters includes one or more control devices, each configured to cyclically realise, at successive time intervals for each reconfigurable connection module of the electric converter, a direct connection, a bypass connection, and a reverse connection.

[0011] It is desirable to improve such control devices to optimize control over the reconfigurable connection modules under both normal operational conditions and in response to external faults.

[0012] It is also desirable to improve said electric converters.

[0013] Aim of the Invention

[0014] The aim of this invention is to provide an improved electric converter and a system equipped with a control device for at least one reconfigurable connection module of the electric converter, which is designed to control one or more reconfigurable connection modules both under normal operating conditions and in the presence of external faults.

[0015] It is an object of the invention an electric converter as claimed in claim 1 , a system as claimed in claim 8, and a network of control devices as claimed in claim 18.

[0016] Further preferred embodiments are described in the dependent claims.

[0017] Attached Figures

[0018] This invention will now be described by way of example, with reference to the accompanying figures, in which:

[0019] Figure 1 shows an electric converter comprising a control device to control the electric converter, according to a first example suitable for understanding the invention;

[0020] Figure 2 illustrates an activation sequence for the electronic switches of a reconfigurable connection module of the electric converter shown in Figure 1 ;

[0021] Figure 3 shows an electric converter according to a second example suitable for understanding the invention;

[0022] Figure 4 shows specialized reconfigurable connection modules for the electric converter shown in Figure 3;

[0023] Figure 5 shows an electrical schematic of an electronic module of the control device shown in Figure 1 ;

[0024] Figure 6 shows an electrical schematic of an electronic module within a control device for the electric converter shown in Figure 3;

[0025] Figure 7 illustrates the output voltage from a reconfigurable connection module as a function of the activation sequence shown in Figure 2, using the excitation voltage; Figure 8 shows the output voltage from a reconfigurable connection module when varying the amplitude of the excitation voltage;

[0026] Figure 9 illustrates the output voltage from a reconfigurable connection module when varying the angle of the excitation voltage;

[0027] Figure 10 shows the output voltage from the electric converter by first adjusting the angle of the excitation voltage, followed by an amplitude adjustment;

[0028] Figure 11 illustrates the output voltage of an output terminal of the electric converter in response to intermittent activation of the enabling commands Ga and Gb;

[0029] Figure 12 shows the output voltage of an output terminal of the electric converter in response to intermittent activation of the enabling commands Ga and Gb’;

[0030] Figure 13 depicts the output voltage from the electric converter in response to freezing the excitation voltage Ve for two cycles and alternately activating the enabling commands Ga and Gb;

[0031] Figure 14 illustrates the output voltage from the electric converter in response to freezing both the excitation voltage Ve and the enabling command Gb for two cycles;

[0032] Figure 15 shows a network of control devices for the electric converters shown in Figures 1 and 3;

[0033] Figures 16A-16C display the interdiction sequence of a DC / DC electric converter;

[0034] Figure 17 shows the output voltage from the electric converter in response to freezing the excitation voltage Ve for half a cycle;

[0035] Figure 18 depicts an electric converter, according to an embodiment of the invention;

[0036] Figure 19 illustrates the output voltage from the electric converter shown in Figure 18 when controlled through the respective excitation voltages Ve;

[0037] Figure 20 shows the waveform of both voltage and current at a terminal of the electric converter shown in Figure 18 when controlled through its respective excitation voltage Ve;

[0038] Figure 21 illustrates the waveform of the currents of the electric converter shown in Figure 18. Detailed Description of the Invention

[0039] Similar parts in the various figures will be denoted by the same reference numbers.

[0040] Referring to Figure 1 , an electric converter 1 is shown, comprising a control device 10 for managing the electric converter 1 .

[0041] Electric converter 1 , which may be an AC / DC, DC / AC, or DC / DC converter, includes three-phase transformer 2 or three single-phase transformers, which define three primary windings 3-R, 3-S, 3-T, and a plurality of secondary windings 4-a...4- n, 5-a...5-n, 6-a...6-n magnetically linked to the three primary windings 3-R, 3-S, 3- T.

[0042] The electric converter 1 also includes a plurality of reconfigurable connection modules 7, 8, 9. Each reconfigurable connection module 7, 8, 9 includes a plurality of electronic switches and is connected on one side to a respective winding from the plurality of secondary windings 4-a...4-n, 5-a...5-n, 6-a...6-n, and on the other side is connected in series with adjacent reconfigurable connection modules.

[0043] Thus, in electric converter 1 , each phase of the secondary side is divided into isolated groups of secondary windings 4-a...4-n, 5-a...5-n, 6-a...6-n connected to their respective reconfigurable electronic modules 7, 8, 9, so as to dynamically vary the transformation ratio according to a harmonic function with a frequency equal to the fundamental.

[0044] In this way, each phase of electric converter 1 produces a wave with an alternating component at double the fundamental frequency and a direct current component. Consequently, by connecting the reconfigurable connection modules of the three phases in series, the alternating components are cancelled, while the direct components are summed.

[0045] Although not shown in Figure 1 , in the DC / DC converter, the primary phases are also divided into isolated groups of turns / windings, each connected to a plurality of reconfigurable connection modules, similar to the secondary phase.

[0046] Referring now to Figure 2, the sequence of activation for the electronic switches in a reconfigurable connection module is described.

[0047] The dynamic variation in the transformation ratio of each phase is achieved by appropriately activating the electronic switches 11 a-16a, 11 b-16b in each of the respective reconfigurable connection modules 7, 8, 9. Specifically, each reconfigurable connection module 7, 8, 9 is assigned with a sequence of specific configurations, each lasting a defined time interval that differs from module to module, reiterating the following order: a) Direct Configuration (“Direct”): wherein the switches in branches 11 and 16 are active for a duration of Ton; b) Bypass Configuration (“Bypass”): wherein the switches in branches 15 and 16 (or alternatively, switches in branches 11 and 13) are active for a duration of Tbypass; c) Reverse Configuration (“Reverse”): wherein the switches in branches 15 and 13 are active for a duration of Ton; d) Bypass Configuration: wherein the switches in branches 15 and 16 (or alternatively, switches in branches 11 and 13) are active for a duration of Tbypass.

[0048] Referring to Figure 3, an example of an electric converter T is shown, which, as an alternative to electric converter 1 in Figure 1 , has two distinct series of specialized reconfigurable connection modules connected in parallel to each other. Specifically, the first series / group of specialized reconfigurable connection modules 7a, 8a, 9a for DC / AC conversion includes a plurality of modules connected in series, while the second series / group of specialized reconfigurable connection modules 7b, 8b, 9b for AC / DC conversion also includes a plurality of modules connected in series.

[0049] Electric converter T, with specialized electronic modules, allows for efficient AC-side power supply to reactive loads in the antenna of significant size, in an efficient way.

[0050] Figure 4 shows a specialized reconfigurable connection module 7a-1 for DC / AC conversion and a specialized reconfigurable connection module 7b-1 for AC / DC conversion.

[0051] These specialized reconfigurable connection modules are based on the reconfigurable connection module 7-1 for the electric converter. Module 7-1 , also shown in Figure 4, includes four pairs of thyristors controllable in conduction and interdiction. One thyristor from each pair is used for rectification (AC / DC, thyristors labelled with subscript “b”), and the other (thyristors labelled with subscript “a”) is used for inversion (DC / AC), as follows: a) a first pair of thyristors 11 a, 11 b arranged in parallel in opposite directions between a first output of a secondary winding 4, 5, or 6 and a first output terminal of the reconfigurable connection module; b) a second pair of thyristors 13a, 13b arranged in parallel in opposite directions between the first output of secondary winding 4, 5, or 6 and a second output terminal of the reconfigurable connection module; c) a third pair of thyristors 15a, 15b arranged in parallel in opposite directions between a second output of secondary winding 4, 5, or 6 and the first output terminal of the reconfigurable connection module; d) a fourth pair of thyristors 16a, 16b arranged in parallel in opposite directions between the second output of secondary winding 4, 5, or 6 and the second output terminal of the reconfigurable connection module.

[0052] Unlike the reconfigurable connection module 7-1 , the specialized reconfigurable connection module 7a-1 for DC / AC conversion includes only the thyristors labelled with subscript “a” for DC / AC inversion, while the specialized reconfigurable connection module 7b-1 for AC / DC conversion includes only the thyristors labelled with subscript “b” for AC / DC rectification.

[0053] Evidently, other types of controllable electronic switches may be used in place of the thyristors shown in Figure 4.

[0054] Referring again to Figure 1 , the control device 10 for electric converter 1 will now be described.

[0055] Control device 10 includes a plurality of electronic modules 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n, each of which can be electrically coupled to a respective reconfigurable connection module within the plurality of reconfigurable connection modules 7, 8, 9, to control the plurality of electronic switches in each reconfigurable connection module to realise, at successive instants and through the plurality of electronic switches: a direct connection (“Direct”) wherein the voltage applied to the input of the reconfigurable connection module is transferred to its output with the same polarity; a bypass connection (“Bypass”) wherein the side connected to the respective secondary winding is isolated, and the side connected in series with adjacent reconfigurable connection modules is short-circuited; a reverse connection (“Reverse”) wherein the voltage applied to the input of the reconfigurable connection module is transferred to its output with reversed polarity.

[0056] Each electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n is activatable in response to an excitation voltage Vea, Veb, having an alternating waveform applied to the input of electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n, which reaches a threshold voltage Vhioi-1 ... Vh i-n, Vh 2-i ... Vh 2- n, Vh 3-i ... Vhio3-n associated with the respective electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n.

[0057] The threshold voltage Vh i-i ... Vhioi-n, Vh 2-i ... Vhio2-n, Vh 3-1 ... Vh s-n differs for each respective electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103- 1 ... 103-n to selectively and cyclically activate a subset of the plurality of electronic modules 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n at successive instants.

[0058] Figure 5 shows an electrical schematic of an electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n of the control device 10, as shown in Figure 1. This electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n may include: a first driving circuit Ca, for controlling a first reconfigurable connection module 7, 8, 9 of a direct-alternating converter ‘DC / AC’ based on a first excitation voltage Vea; and a second driving circuit Cb, for controlling the first reconfigurable connection module 7, 8, 9 of an alternating-direct converter ‘AC / DC’ based on a second excitation voltage Veb.

[0059] The electronic module 101 -1 ...101 -n, 102-1 ... 102-n, 103-1 ... 103-n may be configured to enable the first driving circuit Ca in response to a first enabling command Ga, and enable the second driving circuit Cb in response to a second enabling command Gb, Gb’.

[0060] Thus, enabling command Ga activates the components in the electronic module labelled with subscript ‘a’, for DC / AC conversion; whereas the enabling command Gb activates those labelled with subscript ‘b’, for AC / DC conversion. Therefore, the first driving circuit Ca is disabled in the absence of the first enabling command Ga, and the second driving circuit Cb is disabled in the absence of the second enabling command Gb, Gb’.

[0061] In some cases, a Gb’ command, obtained by simultaneous activation of enabling commands Ga and Gb, may be used to activate the electronic switches labelled with subscript ‘b’ in a sequence different from that provided by command Gb.

[0062] A sleep configuration (“Sleep”) is also possible when all enabling commands Ga, Gb, Gb’ for the gates are inactive, for example, when the electric converter is off or during the transition between AC / DC and DC / AC conversion or vice versa.

[0063] Referring to Figure 5, each driving circuit Ca, Cb may include a plurality of electronic circuits 1011 a-1016a, 1011 b-1016b for driving the respective electronic switches 11 a-16a; 11 b-16b in the respective reconfigurable connection module 7, 8, 9. For example, in Figure 5, the driving circuit Ca, Cb of electronic module 101 -1 controls reconfigurable connection module 7-1 as shown in Figure 2.

[0064] Each electronic circuit 1011 a-1016a, 1011 b-1016b can be activated in response to excitation voltage Vea, Veb applied to its input, when this excitation voltage Vea, Veb reaches its respective threshold Vti 011 , Vtiois, Vtioi 5, Vtioie based on the threshold voltage Vhioi-1 associated with the respective electronic module 101 -1.

[0065] The threshold values Vti 011 , Vti 013, Vti 015, Vtioie differs for each electronic circuit 1011 a-1016a, 1011 b-1016b, allowing selective and cyclic activation of a set of electronic circuits 1011 a-1016a, 1011 b-1016b at successive instants.

[0066] When the excitation voltage Vea or Veb reaches the specific threshold value Vh i-i , it triggers a transition in the electronic module 101 -1 from one configuration to the next, enabling the driving of the reconfigurable connection module 7-1 . Thus, the definition of a threshold voltage Vhioi-1 ... Vh i-n, Vh 2-i ... Vh 2-n, Vhio3-1 ... Vhio3-n for each specific electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103- 1 ... 103-n sets the duration of the Ton / Tbypass intervals for the various configurations of the module itself. The threshold values Vtioi 1 , Vtiois, Vtiois, Vtio are defined as follows:

[0067] Vtion = Vh i-i -A;

[0068] Vtiois — -Vh i-i +A;

[0069] Vtiois = Vh i-i +A;

[0070] Vtiow — -Vh i-i -A; wherein A represents a small overlap interval, for instance, based on the circuit’s hysteresis, which prevents the reconfigurable connection module 7-1 from opening during transitions from one configuration to the next.

[0071] The control device 10 can be configured to periodically adjust the threshold values for the electronic modules 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n, thereby balancing the thermal load across the corresponding electronic switches.

[0072] The table below indicates the excitation voltage ranges for Vea, Veb and the corresponding states of electronic switches, with the specific threshold voltage of a respective electronic module 101 -1 ...101 -n, 102-1 ... 102-n, 103-1 ... 103-n generically represented as “Vh”.

[0073] Table 1 - Activation Ranges for Electronic Switches

[0074] Figure 6 shows an electrical schematic of an electronic module used to control the electrical converter T shown in Figure 3, which differs from the electrical schematic shown in Figure 5 because the first control circuit Ca and the second control circuit Cb are separated from each other. Therefore, the control circuit Ca in Figure 6 will activate a respective reconfigurable connection module with the subscript 'a' for DC / AC conversion; while the control circuit Cb will activate a respective reconfigurable connection module with the subscript 'b' for AC / DC conversion. In this way, two separate sets of modules can be created, each controlled by its own excitation voltage: - the first set of modules, covering all three phases, will be enabled by the activation command Ga and controlled by the three-phase excitation voltage Vea for DC / AC conversion; the second set of modules, covering all three phases, will be enabled by the activation command Gb and controlled by the three-phase excitation voltage Veb for AC / DC conversion.

[0075] The activation intervals for the electronic switches of the specialized modules are shown in Table 2. Table 2 - Activation intervals for the electronic switches

[0076] Referring now to Figure 7, it illustrates the excitation sequence using the excitation voltage Ve (differentiated based on the current direction: "Vea" for DC / AC conversion and "Veb" for AC / DC conversion) to control the plurality of electronic switches 11 a-16a; 11 b-16b in order to realise, at subsequent moments, through the plurality of electronic switches: a direct connection wherein the voltage supplied at the input of the reconfigurable connection module 7, 8, 9 is transferred to its output with the same polarity; a bypass connection wherein the side connected to the respective secondary winding is isolated, and the side connected in series to the adjacent reconfigurable connection modules 7, 8, 9 is short-circuited; a reverse connection wherein the voltage supplied at the input of the reconfigurable connection module 7, 8, 9 is transferred to its output with inverted polarity.

[0077] This excitation sequence allows for the correct, simple, and effective control of each electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n, transitioning from one configuration to the next.

[0078] The control device 10 may include a voltage source to provide, either analogically or digitally, the excitation voltage Ve (Vea or Veb) to each electronic module. For instance, supplying the excitation voltage Ve digitally via an optical fibre with high-frequency sampling promotes galvanic isolation.

[0079] The excitation voltages Vea and Veb have a sinusoidal waveform with a frequency corresponding to the fundamental waveform of the primary winding 3-R, 3-S, 3-T magnetically linked to the secondary winding, which in turn is connected to its respective at least one reconfigurable connection module 7, 8, 9.

[0080] Therefore, the excitation voltages Vea and Veb are three-phase alternating reference voltages, with a frequency equal to the fundamental, wherein each phase is only valid for the electronic modules associated with the corresponding phase.

[0081] Finally, it should be noted that in the bidirectional DC / DC converter, two pairs of three-phase excitation voltages Ve are provided: one pair for the primary / source side (Veal , Veb1 ) and another pair for the secondary / load side (Vea2, Veb2). a) Voltage regulation function during normal operation

[0082] Referring to Figures 8-12, various regulation methods for the control device 10 are described. These methods involve adjusting the excitation voltages Vea, Veb and enabling commands Ga, Gb, Gb’ for different functionalities. a-1) Regulation via excitation voltage variation

[0083] As previously described, excitation voltage Ve (either Vea or Veb) can be used to dynamically adjust the transformation ratio, for example, using a sinusoidal function synchronized with the fundamental.

[0084] To control the output voltage of electric converter 1 and to regulate active and reactive power, control device 10 can adjust the amplitude of excitation voltage Vea, Veb and / or the phase angle with respect to the fundamental. Specifically: by varying the amplitude of excitation voltage Ve, the duration of Ton / T bypass time intervals for each electronic module can be modified, as shown for example in Figure 8; by varying the phase angle of excitation voltage Ve, the time instant of midpoint of Tbypass can be adjusted relative to the zero-crossing of the fundamental wave, as illustrated for example in Figure 9.

[0085] For this purpose, control device 10 can include a voltage regulator to adjust the amplitude of excitation voltage Vea, Veb and / or the phase angle of excitation voltage Vea, Veb.

[0086] In Figure 10, an example is shown during AC / DC conversion, illustrating both the phase shift of input current relative to voltage (in this example, IR relative to VR) and the change in output DC voltage VDC, achieved by first adjusting the phase angle of excitation voltage Ve at instant to and then the amplitude of excitation voltage Ve at instant ti.

[0087] As it is observed, the amplitude variation of excitation voltage Ve has opposite effects depending on the type of conversion, specifically: during AC / DC conversion, reducing the amplitude of excitation voltage Veb decreases the output DC voltage, while increasing the amplitude of excitation voltage Veb increases the output DC voltage; conversely, during DC / AC conversion, reducing the amplitude of excitation voltage Vea increases the output AC voltage amplitude, while increasing the amplitude of excitation voltage Vea decreases the output AC voltage amplitude. a-2) Regulation via Intermittent or Simultaneous Commands

[0088] During DC / AC conversion, if the amplitude of excitation voltage Vea reaches its maximum value, it may no longer be possible to reduce the output AC voltage. This may cause regulation issues, especially with an open AC side or with significant reactive loads.

[0089] In these cases, referring to Figure 1 , the control device 10 of converter 1 can appropriately phase-shift the excitation voltages (Vea vs. Veb) and activate the enable commands intermittently (Ga vs. Gb or Ga vs. Gb’), at a frequency much higher than the fundamental, generating a waveform with a Ga / Gb duty cycle, as shown in Figure 11 , or Ga / Gb’, as illustrated in Figure 12. Alternatively, referring to Figure 3, the control device 10 of converter T can appropriately phase-shift the excitation voltages (Vea vs. Veb) and activate both enable commands Ga and Gb continuously (non-intermittently).

[0090] In particular, control device 10 includes a control logic unit configured to determine whether the amplitude of the first excitation voltage Vea reaches a maximum voltage value, and: i. in response to determining that the amplitude reaches the maximum voltage value, when electric converter 1 comprises a plurality of reconfigurable connection modules 7, 8, 9 connected in series: a. phase-shift the first excitation voltage Vea and the second excitation voltage Veb relative to each other using at least one voltage regulator; and b. activate the first enabling command Ga and the second enabling command Gb, Gb' intermittently and at a frequency higher than the fundamental waveform of the primary winding 3-R, 3-S, 3-T. ii. in response to determining that the amplitude reaches the maximum voltage value, when electric converter T comprises a first group of reconfigurable connection modules 7a, 8a, 9a connected in series and a second group of reconfigurable connection modules 7b, 8b, 9b connected in series and in parallel with the first group of reconfigurable connection modules 7a, 8a, 9a: c. phase-shift the first excitation voltage Vea of the first group of reconfigurable electronic modules 7a, 8a, 9a and the second excitation voltage Veb of the second group of reconfigurable electronic modules 7b, 8b, 9b using at least one voltage regulator; and d. activate the first enabling command Ga for the first group of reconfigurable electronic modules 7a, 8a, 9a, and the second enabling command Gb for the second group of reconfigurable electronic modules 7b, 8b, 9b.

[0091] In this way, an adjustable output voltage can be achieved.

[0092] Specifically, by using commands Ga / Gb or Ga / Gb' intermittently, the following behaviour is obtained: increasing the duration of the enabling command Gb or Gb' relative to Ga will decrease the AC output voltage; decreasing the duration of the enabling command Gb or Gb' relative to Ga will increase the AC output voltage.

[0093] The duty cycle is identical for all three phases and may not vary significantly during the course of the fundamental wave.

[0094] Electric converter 1 may also include one or more filters to remove high- frequency harmonics.

[0095] Furthermore, by paralleling the two series of reconfigurable electronic modules 7a, 8a, 9a, and 7b, 8b, 9b, as shown with reference to electric converter T in Figure 3, activating both enabling commands Ga and Gb continuously (non-intermittently), and phase-shifting the excitation voltages Vea and Veb relative to each other, a more effective voltage control is achieved, even with high reactive currents.

[0096] Therefore, the regulation functionalities described above with reference to electric converter 1 shown in Figure 1 can be applied to electric converter T shown in Figure 3 and the associated control device. b) External fault response functionality

[0097] To address external, short-circuit events to the converter, or in special cases (e.g., during mechanical switch operations to change the operating configuration), control device 10 can act on the excitation voltages Vea and / or Veb, and on the enabling commands Ga and / or Gb, Gb', in the ways indicated below. b-1) AC / DC conversion

[0098] During AC / DC conversion, in the presence of an AC-side short circuit, the control device can disable the enabling commands Ga and Gb, Gb', interrupting the current flow.

[0099] In the presence of a DC-side short circuit or in special cases, the control device can freeze the excitation voltage Ve for a very short time interval, temporarily blocking the transformation ratio of each phase. For this purpose, the voltage source in control device 10 can be configured to freeze excitation voltage Vea, Veb for a predefined freezing time interval in response to a freezing signal.

[0100] Control device 10 can be configured to perform, in response to detecting a DC- side short-circuit current in the AC / DC converter, one of the following actions: i. generate a freezing signal to freeze the first excitation voltage Vea for a predefined freezing time interval and disable the second enabling command Gb, Gb', or generate a freezing signal to freeze the second excitation voltage Veb for a predefined freezing time interval and disable the first enabling command Ga; or ii. generate a freezing signal to freeze both the first excitation voltage Vea and the second excitation voltage Veb for a predefined freezing time interval, and alternately activate the first enabling command Ga and the second enabling command Gb at a frequency equal to the fundamental of the primary winding.

[0101] In this way, the following is generated: a burst of sinusoidal waves on the DC side with a peak value equal to the DC voltage itself, as shown, for example, in Figure 13, if the control device alternately enables commands Gb and Ga at each zero-crossing of the fundamental; a burst of half-waves on the DC side interspersed with half-periods wherein the output voltage is zero, as shown, for example, in Figure 14, if the control device disables both commands Ga and Gb, Gb', or leaves only command Gb, Gb' enabled.

[0102] This can be useful, for instance, to facilitate the extinction of the electric arc during the opening of mechanical switches on the DC side, synchronizing the activation of protections or manoeuvre commands with the temporary freezing of excitation voltage Ve.

[0103] This functionality is particularly important when the fault current exceeds the interruption capacity of the electronic switches in the reconfigurable connection modules 7, 8, 9. By freezing excitation voltage Ve, the switches in the branches of each module that were active at the moment of the short circuit remain active, and the switches of the other branches are not activated until the electrical circuit is opened.

[0104] Synchronization of the activation of protections or manoeuvre commands with the freezing of excitation voltage Ve may also involve coordination among the control devices 10 of the electric converters 1 present in the DC-connected network segment, as shown in Figure 15, to simultaneously perform control actions on all involved electric converters 1 , thereby avoiding additional over currents during the transient. Therefore, the actions (i) and (ii) described above can be performed, alternatively or additionally, in response to detecting a control signal.

[0105] Figure 15 specifically shows a network of control devices 10. Each device 10 includes:

[0106] A communication module adapted to receive / transmit: one or more signals for coordinating the network of control devices, and a freezing signal to freeze the first excitation voltage Vea and / or the second excitation voltage Veb for a predefined freezing time interval, for each control device 10 in the network; and a control logic unit communicatively coupled to the communication module to control the operation of control device 10 in response to one or more control signals and / or the freezing signal. b-2) DC / AC conversion

[0107] During DC / AC conversion, in the presence of a DC-side short circuit, the control device can disable enabling commands Ga and Gb, Gb', interrupting the current flow.

[0108] In contrast, in the presence of an AC-side short circuit, if the fault current exceeds the interruption capacity of the electronic switches of the reconfigurable connection modules 7, 8, 9, the control device 10 can temporarily freeze voltage Ve, alternating or freezing commands Ga and Gb, Gb', as described in the previous section regarding AC / DC conversion, until the electrical circuit is opened.

[0109] For example, control device 10 can be configured to perform, in response to detecting a short-circuit current in the AC / DC converter, one of the following actions: i. generate a freezing signal to freeze the first excitation voltage Vea for a predefined freezing time interval and disable the second enabling command Gb, Gb', or generate a freezing signal to freeze the second excitation voltage Veb for a predefined freezing time interval and disable the first enabling command Ga; or ii. generate a freezing signal to freeze both the first excitation voltage Vea and the second excitation voltage Veb for a predefined freezing time interval, and alternately activate the first enabling command Ga and the second enabling command Gb at a frequency equal to the fundamental of the primary winding.

[0110] In this way, the activation of electronic switches in the branches inactive, at the time of the fault, is avoided; which if added to the switches that remained active due to failed interdiction, could short-circuit the converter on the DC side.

[0111] This procedure may also involve, alternatively or additionally, coordination among control devices 10 of converters 1 present in the DC-connected network segment, as described in the previous section. b-3) DC / DC conversion

[0112] During DC / DC conversion, in the presence of a source-side short circuit, the control device can simply disable commands Ga and Gb, Gb' on both sides, interrupting the current flow.

[0113] In the presence of a load-side short circuit, however, if the fault current exceeds the interruption capacity of the electronic switches in the reconfigurable connection modules 7, 8, 9, the control device can disable the enabling commands Ga and Gb, Gb' on the load side and abruptly vary the angle of excitation voltage Ve on the source side, for example by 90°, if necessary, one phase at a time in succession, to interrupt the current flow.

[0114] For instance, in the presence of a short circuit, control device 10 can be configured to disable the second enabling command Gb of the AC / DC converter and vary the angle of the first excitation voltage Vea of the DC / AC converter, one phase at a time, when the DC / AC electric converter and the AC / DC electric converter form a DC / DC converter using a single three-phase transformer 2.

[0115] In other words, when the DC / AC electric converter and the AC / DC electric converter form a DC / DC converter with a common three-phase magnetic core, in the presence of a short circuit, control device 10 can be configured to disable the second enabling command Gb, Gb' of the AC / DC converter and vary the angle of the first excitation voltage Vea of the DC / AC converter, to force the interdiction of the electronic switches in each phase by exploiting the magnetic flux linked to the other two phases.

[0116] Figures 16A-16C show the interdiction sequence of a DC / DC electric converter.

[0117] In Figure 16A, when a reconfigurable connection module 7, 8, 9 of a sourceside phase is in the "Direct" configuration, i.e., when electronic switches 11 a and 16a of the module are active, and when a reconfigurable connection module 7, 8, 9 of the same phase on the load side is also in the "Direct" configuration, i.e., when the electronic switches of that module 11 b and 16b have remained active due to failed interdiction, varying the angle of excitation voltage Ve on the source side, for example by 90°, activates the "Reverse" configuration (in which switches 15a and 13a are active) only on the source side, consequently causing the interdiction of the switches of the previous configuration on the source side (Figure 16B) and on the load / consumption side (Figure 16C). This is possible provided that the converter is realized using a single three- phase transformer. In this case, in the event of a sudden angle variation of one phase of excitation voltage Ve, the magnetic flux linked to the other two phases sustains the voltage across the isolated groups of turns of the phase under consideration, forcing the interdiction of the switches of the previous configuration.

[0118] The fault response functionalities described above with reference to electric converter 1 shown in Figure 1 can be applied to electric converter T shown in Figure 3 and the associated control device. c) Improved electric converter with DC voltage sign reversal functionality

[0119] The mechanism of freezing the excitation voltage Ve for a very brief time (e.g., half a cycle), for instance, by coordinating control devices 10 present in a network segment, can be used to reverse the sign of the DC voltage, as shown with reference to Figure 17.

[0120] For this purpose, the voltage source in control device 10 can be configured to freeze excitation voltage Vea, Veb for a predefined freezing time interval in response to a freezing signal and / or periodically.

[0121] After the reversal, the roles of enabling commands Ga and Gb switch: command Ga activates the electronic switches labelled with subscript 'a', but this time for AC / DC conversion, while command Gb activates those labelled with subscript 'b' for DC / AC conversion.

[0122] By performing this reversal periodically (depending on the climatic zone, air salinity, etc.), it is possible to operate overhead lines in DC, avoiding polarization of sediments on insulators.

[0123] The functionalities of reversing the sign of the DC voltage described above with reference to electric converter 1 shown in Figure 1 can be applied to electric converter T shown in Figure 3 and the associated control device. d) Electric converter with cyclic unipolar inversion

[0124] Continuing to refer to Figures 1 -17, Figure 18 illustrates an embodiment of a system SC comprising the electric converter 1" described above and the control device 10 electrically coupled to electric converter 1".

[0125] This embodiment differs from electric converters 1 , T shown in Figures 1 and 3 at least in that it includes three terminals R', S', T' to obtain or receive three direct voltages and to operate cyclic unipolar inversion of the voltages at respective terminals R', S', T'.

[0126] The same reference numbers designate parts, elements, or components identical or corresponding to those already illustrated in Figures 1 -17 and described above, which will not be described again.

[0127] In particular, electric converter 1" comprises a plurality of primary windings 3- R, 3-S, 3-T and a plurality of secondary windings 4-a...4-n, 5-a...5-n, 6-a...6-n magnetically linked to the plurality of primary windings 3-R, 3-S, 3-T.

[0128] Although Figure 18 shows a three-phase transformer, it will be evident to those skilled in the art that electric converter 1" may alternatively include a plurality of single-phase transformers or a plurality of three-phase transformers — for example, three single-phase transformers, nine single-phase transformers, or, in other cases, three three-phase transformers.

[0129] As shown in Figure 18, the secondary windings 4-a...4-n, 5-a...5-n, 6-a...6-n comprise a first set of secondary windings 4-a...4-n magnetically linked to the first primary winding 3-T, a second set of secondary windings 5-a...5-n magnetically linked to the second primary winding 3-S, and a third set of secondary windings 6- a...6-n magnetically linked to a third primary winding 3-R.

[0130] Electric converter 1" also includes a plurality of reconfigurable connection modules as described with reference to Figure 4.

[0131] Each reconfigurable connection module comprises a plurality of electronic switches configured to perform at successive instants: a direct connection wherein the voltage applied to the input of the respective reconfigurable connection module is transferred to its output with the same polarity; a bypass connection wherein the side of the respective reconfigurable connection module connected to the respective secondary winding is isolated, and the side connected in series with adjacent reconfigurable connection modules is short-circuited; a reverse connection wherein the voltage applied to the input of the respective reconfigurable connection module is transferred to its output with inverted polarity.

[0132] The plurality of reconfigurable connection modules is organized into groups of connection modules to form a plurality of groups of reconfigurable connection modules connected to three terminals R', S', T' of electric converter 1", to obtain a voltage pattern at the three terminals R', S', T', as shown, for example, in Figure 19. This pattern can vary over time in a cyclic manner, as will be described later.

[0133] In Figure 18, for simplicity, only two reconfigurable connection modules per phase and per respective terminal R', S', T' are depicted; however, it will be evident to those skilled in the art that the number of reconfigurable connection modules can be chosen based on the maximum voltage that the modules can withstand and the DC voltage desired to be obtained or received from the terminal R', S', T' associated with them.

[0134] Each group of reconfigurable connection modules comprises: a first set of reconfigurable connection modules 7x, 7y, 7z electrically coupled to the first set of secondary windings 4-a...4-n, a second set of reconfigurable connection modules 8x, 8y, 8z electrically coupled to the second set of secondary windings 5-a...5-n, and a third set of reconfigurable connection modules 9x, 9y, 9z electrically coupled to the third set of secondary windings 6-a...6-n.

[0135] These groups of reconfigurable connection modules can be connected to each other to form a star (wye) connection relative to a common terminal Ct of electric converter 1", or they can be connected to form a delta connection. In the delta connection, the number of modules and windings can be greater than the number required for the star connection.

[0136] In the delta connection case, each group of reconfigurable connection modules can have one end electrically coupled to an end of one of the remaining groups to form a closed circuit of a plurality of groups of reconfigurable connection modules. In this case, the three terminals R', S', T' are arranged at the respective ends.

[0137] For example, in the delta connection, the plurality of groups of reconfigurable connection modules may comprise: a first group of reconfigurable connection modules 7x, 8x, 9x connected in series along a first branch r of electric converter 1", wherein the first branch r includes a reference terminal R' located at the end of the first group of reconfigurable connection modules 7x, 8x, 9x; a second group of reconfigurable connection modules 7y, 8y, 9y connected in series along a second branch s of electric converter 1", wherein the second branch s includes a secondary terminal S' located at the end of the second group of reconfigurable connection modules 7y, 8y, 9y; and a third group of reconfigurable connection modules 7z, 8z, 9z connected in series along a third branch t of electric converter 1", wherein the third branch t includes a tertiary terminal T' located at the end of the third group of reconfigurable connection modules 7z, 8z, 9z.

[0138] In this case, reference terminal R' is common to the first branch r and the second branch s, secondary terminal S' is common to the second branch s and the third branch t, and tertiary terminal T' is common to the third branch t and the first branch r.

[0139] Alternatively, in the star connection shown in Figure 18, these groups of reconfigurable connection modules may comprise: a first group of reconfigurable connection modules 7x, 8x, 9x connected in series along a first branch r of electric converter 1", wherein the first branch r includes a reference terminal R' located distally with respect to the common terminal Ct; a second group of reconfigurable connection modules 7y, 8y, 9y connected in series along a second branch s of electric converter 1", wherein the second branch s includes a secondary terminal S' located distally with respect to the common terminal Ct; and a third group of reconfigurable connection modules 7z, 8z, 9z connected in series along a third branch t of electric converter 1", wherein the third branch t includes a tertiary terminal T' located distally with respect to the common terminal Ct.

[0140] In general, the reconfigurable connection modules can be driven by their respective control device 10 through their respective excitation voltages Ve, so as to have two poles with opposite voltage and one pole (in turn) undergoing voltage inversion.

[0141] Control device 10 is generally described with reference to Figures 1 -17. Figure 18 shows a system SC comprising the electric converter 1" described above and control device 10 electrically coupled to electric converter 1".

[0142] In this case, control device 10 is configured to control electric converter 1" to achieve, in successive time intervals, a cyclic sequence of polarity inversion of the three voltages at the three terminals R', S', T' of electric converter 1" relative to the common terminal Ct in the star connection, or relative to ground in the delta connection. Control device 10 also allows maintaining, in these time intervals, while one of the three terminals is in the process of polarity inversion, the remaining terminals at voltages with opposite polarity relative to each other. Through the cyclic sequence of polarity inversion, one of the remaining terminals will have a voltage with opposite polarity compared to its voltage in the previous time interval.

[0143] An example of a cyclic sequence of polarity inversion of the three voltages at respective terminals R', S', T' is provided in Table 3.

[0144] Table 3 - Example of cyclic unipolar inversion sequence for the DC polarity of the direct voltages.

[0145] With reference to Table 3 above, the cyclic polarity inversion sequence of the three voltages can include: a first interval t1 , t3, in which secondary terminal S’ is maintained at a polarity opposite to that of tertiary terminal T’; a second interval t2, t4, in which secondary terminal S’ is maintained at a polarity opposite to that of reference terminal R’; and a third interval t3, t5, in which reference terminal R’ is maintained at a polarity opposite to that of tertiary terminal T’.

[0146] Figure 19 illustrates the waveforms of the voltages at terminals R’, S’, and T’ of electric converter 1” shown in Figure 18, at the respective instants indicated in Table 3. In Figure 19, each voltage at terminals R’, S’, and T’ has an alternating square waveform at a frequency lower than the fundamental, for example, with a frequency of 2 Hz. The voltages at terminals R’, S’, and T’ are superimposable at any instant, such that, when overlapped, a continuous DC voltage is obtained. This makes it possible to maintain a continuous voltage at all three terminals R’, S’, T’.

[0147] The three terminals R’, S’, T’ can therefore be configured to emit or receive such waveforms, respectively, to achieve an alternating-to-direct (AC / DC) or direct- to-alternating (DC / AC) conversion.

[0148] As indicated in Figures 1 -17, control device 10 can include multiple electronic modules 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n, each module being electrically coupled to a respective reconfigurable connection module from the plurality of connection modules. This arrangement controls the electronic switches such that, at successive instants, it achieves the direct connection, bypass connection, and reverse connection.

[0149] Each electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n can be activated in response to an excitation voltage Vea, Veb, with an alternating waveform at the input of the electronic module 101 -1 ... 101 -n, 102-1 ... 102-n, 103- 1 ... 103-n, reaching a threshold voltage value Vh i-i ... Vhioi-n, Vh 2-i ... Vh 2-n, Vh 3-i ... Vhio3-n associated with the respective electronic module 101 -1 ...101 -n, 102-1 ... 102-n, 103-1 ... 103-n. The threshold voltage value is different for each respective electronic module, allowing it to selectively and cyclically activate a subset of the plurality of electronic modules 101 -1 ...101 -n, 102-1 ... 102-n, 103- 1 ... 103-n at these successive instants.

[0150] The polarity inversion can be sudden, by freezing the respective excitation voltage Ve (Vea, Veb) for a very short time (e.g., half a cycle), or it can be slower (with a configurable time, but greater than half a cycle) for example, by sequentially reducing the amplitude of the excitation voltage Ve, changing the polarity, and then increasing the amplitude of the excitation voltage Ve. Additionally, by controlling the amplitude of the excitation voltages Ve (Vea, Veb) for the groups of modules connected to terminals with similar polarity, load transfer can be performed before each polarity inversion.

[0151] Figure 20 illustrates the waveforms of both voltage and current at a terminal R’, S’, or T’ of electric converter 1 ” shown in Figure 18 when driven by the respective excitation voltage Ve.

[0152] From Figure 20, the various operating instants of any of the terminals R’, S’, or T’ of the star-connected branches can be observed. The specific example highlights the various operating instants of terminal R’, which follow cyclically, as shown: in the period immediately preceding instant ts, terminal R’ is maintained at a voltage equal to the maximum VR\ In this period, terminal R’ operates in “single mode,” meaning it has a polarity opposite to the remaining terminals S’ and T’. In the example shown in Figure 20, terminal R’ has a positive polarity at instant ts; after instant ts, terminal R’ has the same polarity as another terminal S’ or T’ that has just completed a polarity inversion; during the interval ts-ta, load transfer occurs: the current in the first branch r of terminal R’ decreases (releasing the load) while the other terminal S’ or T’ (accepting the load) sees an increase in current; at instant ta, the current in the first branch r is almost null, and terminal R’ has thus released the load; after instant ta, polarity inversion of terminal R’ begins at nearly zero current. The polarity inversion takes place over the interval ta-tP. The length of the interval ta-tPcan be regulated based on the excitation voltage Ve, as previously described; after instant tP, the current in the first branch r of terminal R’ increases as it takes on the load. During the interval tP-tk, terminal R’ has the same polarity as another terminal that has just finished single-mode operation and is releasing the load; at instant tk, terminal R’ is once again maintained at a voltage equal to the maximum VR’ but with polarity opposite to its polarity at instant ts. In the period immediately after instant tk, terminal R’ operates again in “single mode,” having polarity opposite to the remaining terminals S’ and T’.

[0153] The currents of poles R’, S’, and T’ will thus have a trapezoidal shape at a frequency lower than the fundamental, as shown in Figure 21 , which illustrates the current waveforms of electric converter 1” shown in Figure 18.

[0154] From Figure 21 , it can be observed that the effective current value for poles R’, S’, and T’ is 2 / 3 of the peak value, enabling a uniform distribution of thermal stress along the respective branches r, s, and t. This ensures that thermal load is evenly distributed, preventing hotspots and further increasing the efficiency of electric converter 1”.

[0155] Furthermore, this solution allows the utilization of the transmission capacity of all three terminals R’, S’, T’.

[0156] Advantageously, control device 10 allows selective and cyclical control of at least one reconfigurable connection module in electric converters 1 , T, 1”. Furthermore, control device 10 within the SC system, as described in this invention, enables proper control of the terminal voltage in electric converter 1” through excitation voltages Ve.

[0157] A second advantage is that control device 10 permits accurate control of one or more reconfigurable connection modules in electric converters 1 , T, 1” under normal operating conditions and / or in the presence of external faults.

[0158] Advantageously, electric converter 1” as described in this invention can increase transmission capacity of overhead lines and cable lines by about 40%, as all three terminals R’, S’, T’ can be utilized, and the voltage at each terminal — except during switching — is equal to the peak value of the sinusoidal voltage. Additionally, electric converter 1” as described in this invention can reduce reactive power by lowering the frequency, which leads to increased voltage stability, reduced losses in overhead lines and electrical cables, and eliminates the need for compensation reactors in cable lines, which are typically used to balance the capacitive behaviour of electric cables.

[0159] Moreover, by cyclically varying polarities, sediment polarization on insulators can be prevented.

[0160] The network of control devices 10 in this invention advantageously allows simultaneous control actions on all involved electric converters 1 , T, 1”.

[0161] The present invention has been described for illustrative, but not limitative, purposes, according to the preferred embodiments, but it is understood that variations and / or modifications may be made by those skilled in the field without departing from the scope defined by the appended claims.

[0162] The current teaching can also extend to one or more of the following numbered clauses:

[0163] 1 . A control device (10) for an electric converter (1 , T) that includes: a three-phase transformer (2) or three single-phase transformers defining:

[0164] • three primary windings (3-R, 3-S, 3-T); and

[0165] • a plurality of secondary windings (4-a...4-n, 5-a...5-n, 6-a...6-n) magnetically linked to said three primary windings (3-R, 3-S, 3-T); and a plurality of reconfigurable connecting modules (7, 8, 9) each of which comprises a plurality of electronic switches and is connected on one side to a respective winding of said plurality of secondary windings (4-a...4-n, 5-a...5-n, 6- a...6-n) and on the other side is connected in series with the adjacent reconfigurable connecting modules; said control device (10) comprising: a plurality of electronic modules (101 -1 ...101 -n, 102-1 ... 102-n, 103-1 ... 103- n), each module being electrically couplable to a respective reconfigurable connecting module of said plurality of reconfigurable connecting modules (7, 8, 9), for controlling said plurality of electronic switches so as to realize in successive instants, and by means of said plurality of electronic switches:

[0166] • a direct connection wherein the voltage supplied to the input of the reconfigurable connecting module is transferred to its output with the same polarity;

[0167] • a bypass connection wherein the side connected to the respective secondary winding is isolated and the side connected in series with the adjacent reconfigurable connecting modules is short-circuited; and

[0168] • a reverse connection wherein the voltage supplied to the input of the reconfigurable connecting module is transferred to its output with reversed polarity; each electronic module (101 -1 ...101 -n, 102-1 ... 102-n, 103-1 ... 103-n) being activated in response to an excitation voltage (Vea, Veb), having an alternate waveform at the input of the electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-

[0169] 1 ... 103-n), which reaches a threshold voltage value (Vhioi-i...Vhioi-n, Vh 2-

[0170] 1...Vhio2-n, Vhio3-i ...Vhio3-n) associated with said electronic module (101 -1 ...102-n, 103-1 ... 103-n), said threshold voltage value being different for each respective electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) so as to selectively and cyclically activate a set of said plurality of electronic modules (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) in said successive instants. 2. Control device (10) according to clause 1 , comprising a voltage source for providing to each electronic module said excitation voltage (Vea, Veb), wherein said excitation voltage (Vea, Veb) is a three-phase voltage and has a sinusoidal waveform with a frequency equal to the fundamental waveform of the primary winding (3-R, 3-S, 3-T), said primary winding (3-R, 3-S, 3-T) being magnetically concatenated to said secondary winding, which is connected to said respective at least one reconfigurable connecting module (7, 8, 9).

[0171] 3. Control device (10) according to clause 2, wherein said voltage source is configured to freeze said excitation voltage (Vea, Veb) for a predefined freezing time interval in response to a freezing signal and / or periodically.

[0172] 4. Control device (10) according to any one of the preceding clauses, comprising a voltage regulator to change the amplitude of said excitation voltage (Vea, Veb) and / or the angle of said excitation voltage (Vea, Veb).

[0173] 5. Control device (10) according to any one of the preceding clauses, wherein said electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) comprises: a first driving circuit (Ca), for controlling a first reconfigurable connecting module (7, 8, 9) of a direct-alternating converter ‘DC / AC’ as a function of a first excitation voltage (Vea); and a second driving circuit (Cb), for controlling said first reconfigurable connecting module (7, 8, 9) of a direct-alternating converter ‘AC / DC’ as a function of a second excitation voltage (Veb); said electronic module (101 -1 ...101 -n, 102-1 ... 102-n, 103-1 ... 103-n) being configured to:

[0174] • enable said first driving circuit (Ca) in response to a first enabling command (Ga), and

[0175] • enable said second driving circuit (Cb) in response to a second enabling command (Gb, Gb').

[0176] 6. Control device (10) of clause 5, wherein said first driving circuit is disabled in the absence of said first enabling command (Ga), and wherein said second driving circuit (Cb) is disabled in the absence of said second enabling command (Gb, Gb').

[0177] 7. Control device (10) of clause 5 or 6, comprising a logic control unit configured to determine whether the amplitude of said first excitation voltage (Vea) reaches a maximum voltage value, and i. in response to a determination that said amplitude reaches said maximum voltage value, when said electric converter (1 ) comprises a plurality of reconfigurable connecting modules (7, 8, 9) connected in series with respect to each other: a. phase-shift from each other, by means of at least one voltage regulator, said first excitation voltage (Vea) and said second excitation voltage (Veb); and b. activate said first enabling command (Ga) and said second enabling command (Gb, Gb') intermittently and at a higher frequency than the fundamental wave form of the primary winding (3 - R, 3 - S, 3 - T ); ii. in response to a determination that said amplitude reaches said maximum voltage value, when said electric converter (1 ') comprises a first group of reconfigurable connecting modules (7a, 8a, 9a) connected in series with each other and a second group of reconfigurable connecting modules (7b, 8b, 9b) connected in series with each other and in parallel to said first group of reconfigurable connecting modules (7a, 8a, 9a): a. phase-shift from each other, by means of at least one voltage regulator, said first excitation voltage (Vea) of said first group of reconfigurable electronic modules (7a, 8a, 9a), and said second excitation voltage (Veb) of said second group of reconfigurable electronic modules (7b, 8b, 9b); and b. activate said first enabling command (Ga) of said first group of reconfigurable electronic modules (7a, 8a, 9a), and said second enabling command (Gb) of said second group of reconfigurable electronic modules (7b, 8b, 9b).

[0178] 8. Control device (10) according to any one of clauses 5-7, being configured to perform, in response to a detection of a short-circuit current in said AC / DC converter or DC / AC converter and / or a control signal, one of the following actions:

[0179] (i) disabling said first enabling command (Ga) and said second enabling command (Gb, Gb'); or

[0180] (ii) generating a freezing signal to freeze said first excitation voltage (Vea) for a default freezing time interval and disabling said second enabling command (Gb, Gb'), or generating a freezing signal to freeze said second excitation voltage (Veb) for a default freezing time interval and disabling said first enabling command (Ga); or

[0181] (iii) generating a freezing signal to freeze said first excitation voltage (Vea) and said second excitation voltage (Veb) for a default freezing time interval, and alternately activating said first enabling command (Ga) and said second enabling command (Gb) at a frequency equal to the fundamental of the primary winding; or

[0182] (iv) disabling said second enabling command (Gb, Gb') of the AC / DC converter and varying the angle of said first excitation voltage (Vea) of the DC / AC converter, preferably wherein disabling said second enabling voltage (Gb, Gb') and varying the angle of said first excitation voltage (Vea) are performed one step at a time, when said DC / AC electric converter and said AC / DC electric converter form a DC / DC converter using only one three-phase transformer (2).

[0183] 9. Network of control devices (10) according to any one of the preceding clauses, each device (10) comprising: a communication module adapted to receive / transmit:

[0184] • one or more signals for coordinating said network of control devices, and

[0185] • a freezing signal to freeze said first excitation voltage (Vea) and / or said second excitation voltage (Veb) for a default freezing time interval, for each control device (10) of said network; and a control logic unit communicatively coupled to said communication module to control the operation of said control device (10) in response to said one or more control signals and / or said freezing signal.

Claims

CLAIMS1 . Electric converter (1 ") comprising: a plurality of primary windings (3-R, 3-S, 3-T); a plurality of secondary windings (4-a...4-n, 5-a...5-n, 6-a...6-n) magnetically linked to said plurality of primary windings (3-R, 3-S, 3-T), said plurality of secondary windings (4-a...4-n, 5-a...5-n, 6-a...6-n) comprising a first set of secondary windings (4-a...4-n) magnetically linked to a first primary winding (3-T) of said plurality of primary windings, a second set of secondary windings (5- a...5-n) magnetically linked to a second primary winding (3-S) of said plurality of primary windings, and a third set of secondary windings (6-a...6-n) magnetically linked to a third primary winding (3-R) of said plurality of primary windings; and a plurality of groups of reconfigurable connecting modules connected to three terminals (R’, S’, T’) of said electric converter (1") to obtain a configurable voltage pattern on said three terminals (R’, S’, T’), wherein each group of said plurality of groups of reconfigurable connecting modules comprises:- a first set of reconfigurable connecting modules (7x, 7y, 7z) electrically coupled to said first set of secondary windings (4-a...4-n),- a second set of reconfigurable connecting modules (8x, 8y, 8z) electrically coupled to said second set of secondary windings (5-a...5-n), and- a third set of reconfigurable connecting modules (9x, 9y, 9z) electrically coupled to said third set of secondary windings (6-a...6-n); wherein each reconfigurable connecting module comprises a plurality of electronic switches configured to perform in successive instants:- a direct connection wherein the voltage applied to the input of the respective reconfigurable connecting module is transferred to its output with the same polarity;- a bypass connection wherein the side of the respective reconfigurable connecting module connected to the respective secondary winding is isolated, and the side connected in series to adjacent reconfigurable connecting modules is short-circuited; anda reverse connection wherein the voltage applied to the input of the respective reconfigurable connecting module is transferred to its output with inverted polarity.

2. Electric converter (1 ") according to claim 1 , wherein said plurality of groups of reconfigurable connecting modules are connected to each other to form a delta connection, wherein each group of reconfigurable connecting modules has one end electrically coupled to one end of one of the remaining groups to form a closed circuit of a plurality of reconfigurable connecting modules, said three terminals (R’, S’, T’) being arranged at said respective ends.

3. Electric converter (1") according to claim 2, wherein said plurality of groups of reconfigurable connecting modules comprises: a first group of reconfigurable connecting modules (7x, 8x, 9x) connected in series along a first branch (r) of the electric converter (1"), wherein said first branch (r) comprises a reference terminal (R’) located at said end of said first group of reconfigurable connecting modules (7x, 8x, 9x); a second group of reconfigurable connecting modules (7y, 8y, 9y) connected in series along a second branch (s) of the electric converter (1"), wherein said second branch (s) comprises a secondary terminal (S’) located at said end of said second group of reconfigurable connecting modules (7y, 8y, 9y); and a third group of reconfigurable connecting modules (7z, 8z, 9z) connected in series along a third branch (t) of the electric converter (1"), wherein said third branch (t) comprises a tertiary terminal (T’) located at said end of said first group of reconfigurable connecting modules (7z, 8z, 9z); wherein the reference terminal (R’) is common to said first branch (r) and said second branch (s), the secondary terminal (S’) is common to said second branch (s) and said third branch (t), and the tertiary terminal (T’) is common to said third branch (t) and said first branch (r).

4. Electric converter (1 ") according to claim 1 , wherein said plurality of groups of reconfigurable connecting modules are connected to each other to form a star connection relative to a common terminal (Ct) of said electric converter (1").

5. Electric converter (1") according to claim 4, wherein said plurality of groups of reconfigurable connecting modules comprises: a first group of reconfigurable connecting modules (7x, 8x, 9x) connected in series along a first branch (r) of the electric converter (1"), wherein said first branch (r) comprises a reference terminal (R’) located distally with respect to said common terminal (Ct); a second group of reconfigurable connecting modules (7y, 8y, 9y) connected in series along a second branch (s) of the electric converter (1"), wherein said second branch (s) comprises a secondary terminal (S’) located distally with respect to said common terminal (Ct); and a third group of reconfigurable connecting modules (7z, 8z, 9z) connected in series along a third branch (t) of the electric converter (1"), wherein said third branch (t) comprises a tertiary terminal (T) located distally with respect to said common terminal (Ct).

6. Electric converter (1 ") according to any of the preceding claims, wherein each of said three terminals (R’, S’, T’) is configured to emit or receive a square waveform voltage at a frequency lower than the fundamental frequency.

7. Electric converter (1 ") according to any of the preceding claims, wherein said three terminals (R’, S’, T’) are configured to emit or receive voltages that can be superimposed so that, when superimposed, a continuous DC voltage is obtained.

8. System (SC) comprising: an electric converter (1") according to any of the preceding claims, and a control device (10) electrically coupled to said electric converter (1") and configured to control said electric converter (1") to realise, in successive time intervals, a cyclic sequence of polarity inversion of the three voltages at said three terminals (R’, S’, T’) of the electric converter (1"); and maintain, in said successive time intervals, and while one of said three terminals is in the phase of polarity inversion, the remaining terminals at voltageswith opposite polarity relative to each other, wherein one of the remaining terminals has voltage with polarity opposite to its voltage in the previous interval.

9. System (SC) according to claim 8, wherein said cyclic sequence of polarity inversion of the three voltages comprises: a first interval (t1 , t3), wherein the secondary terminal (S’) of said three terminals is maintained at a voltage with polarity opposite to the voltage of the tertiary terminal (T); a second interval (t2, t4), wherein the secondary terminal (S’) is maintained at a voltage with polarity opposite to the reference terminal (R’); and a third interval (t3, t5), wherein the reference terminal (R’) is maintained at a voltage with polarity opposite to the tertiary terminal (T’).

10. System (SC) according to claim 8 or 9, wherein said control device (10) comprises a plurality of electronic modules (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n), each module being electrically coupled to a respective reconfigurable connecting module of said plurality of groups of reconfigurable connecting modules, to control the plurality of electronic switches to perform in said successive instants, said direct connection, said bypass connection, and said reverse connection; each electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) being activatable in response to an excitation voltage (Vea, Veb), having an alternate waveform at the input of the electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n), which reaches a threshold voltage value (Vhioi-1 ... Vh i-n, Vh 2-i ... Vhio2-n, Vh 3-i ... Vhio3-n) associated with said respective electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n), said threshold voltage value being different for each respective electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) so as to selectively and cyclically activate a set of said plurality of electronic modules (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) in said successive instants.11 . System (SC) according to claim 10, said control device (10) comprising a voltage source for providing to each electronic module said excitation voltage (Vea, Veb), wherein said excitation voltage (Vea, Veb) is a three-phase voltageand has a sinusoidal waveform with a frequency equal to the fundamental waveform of the primary winding (3-R, 3-S, 3-T),12. System (SC) according to claim 11 , wherein said control device (10) comprising at least a voltage source configured to freeze said excitation voltage (Vea, Veb) for a predefined freezing time interval in response to a freezing signal and / or periodically.13 System (SC) according to any one of claims 8-12, wherein said control device (10) comprises a voltage regulator to change the amplitude of said excitation voltage (Vea, Veb) and / or the angle of said excitation voltage (Vea, Veb).14 System (SC) according to any one of the claims 8-13, wherein said electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) comprises: a first driving circuit (Ca), for controlling a first reconfigurable connecting module (7r-t, 8r-t, 9r-t) of the electric converter (1”) as a function of a first excitation voltage (Vea), said electric converter (1”) being a direct-alternating converter ‘DC / AC’; and a second driving circuit (Cb), for controlling said first reconfigurable connecting module (7r-t, 8r-t, 9r-t) of the electric converter (1”) as a function of a second excitation voltage (Veb), said electric converter (1”) being a direct-alternating converter ‘AC / DC’; said electronic module (101 -1 ... 101 -n, 102-1 ... 102-n, 103-1 ... 103-n) being configured to:• enable said first driving circuit (Ca) in response to a first enabling command (Ga), and• enable said second driving circuit (Cb) in response to a second enabling command (Gb, Gb').15 System (SC) of claim 14, wherein said first driving circuit is disabled in the absence of said first enabling command (Ga), and wherein said second driving circuit (Cb) is disabled in the absence of said second enabling command (Gb, Gb').

16. System (SC) of claim 14 or 15, comprising a logic control unit configured to determine whether the amplitude of said first excitation voltage (Vea) reaches a maximum voltage value, and i. in response to a determination that said amplitude reaches said maximum voltage value: a. phase-shift from each other, by means of at least one voltage regulator, said first excitation voltage (Vea) and said second excitation voltage (Veb); and b. activate said first enabling command (Ga) and said second enabling command (Gb, Gb') intermittently and at a higher frequency than the fundamental wave form of the primary winding (3 - R, 3 - S, 3 - T).

17. System (SC) according to any one of claims 14-16, being configured to perform, in response to a detection of a short-circuit current in any branch (r, s, t) of said electric converter (1”) and / or a control signal, one of the following actions:(i) disabling said first enabling command (Ga) and said second enabling command (Gb, Gb'); or(ii) generating a freezing signal to freeze said first excitation voltage (Vea) for a default freezing time interval and disabling said second enabling command (Gb, Gb'), or generating a freezing signal to freeze said second excitation voltage (Veb) for a default freezing time interval and disabling said first enabling command (Ga); or(iii) generating a freezing signal to freeze said first excitation voltage (Vea) and said second excitation voltage (Veb) for a default freezing time interval, and alternately activating said first enabling command (Ga) and said second enabling command (Gb) at a frequency equal to the fundamental of the primary winding; or(iv) disabling said second enabling command (Gb, Gb') of the AC / DC converter and varying the angle of said first excitation voltage (Vea) of the DC / AC converter, wherein said DC / AC electrical converter and said AC / DC electrical converter form a DC / DC converter that includes at least one three-phase core, in such a way as to force the interdiction of the electronic switches of each phase by exploiting the magnetic flux linked to the other two phases.

18. Network of control devices (10) of the system (SC) according to any one of claims 10-17, each device (10) comprising:a communication module adapted to receive / transmit:• one or more signals for coordinating said network of control devices (10), and• a freezing signal to freeze said first excitation voltage (Vea) and / or said second excitation voltage (Veb) for a default freezing time interval, for each control device (10) of said network; and a control logic unit communicatively coupled to said communication module to control the operation of said control device (10) in response to said one or more control signals and / or said freezing signal.

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