Converter device

Abstract

A converter arrangement (10A) comprises at least one first string of electrically interconnected modules (12A, 14A, 16A, 18A, 20A, 22A) and a first shield and a second shield (24A, 26A), wherein the first shield (24A) is connected to a first defined potential and placed adjacent to a first group of modules (G1A) in said first string comprising at least one first module (14A), and the second shield (26A) is connected to a second defined potential and placed adjacent to a second group of modules (G2A) in said first string comprising at least one second module (18A), wherein, in operation, a resonance loop is created from the first module (14A) via the first and second shields (24A, 26A) and the second module (18A) back to the first module (14A), and the converter arrangement further comprises a damping unit (32A) in the resonance loop, said damping unit being arranged to damp electromagnetic noise.

Description

TECHNICAL FIELD

[0001] The present invention relates to a converter arrangement comprising at least one string of electrically interconnected modules. BACKGROUND

[0002] Today, converter stations for high voltage direct current (HVDC) and flexible alternating current transmission system (FACTS) applications are typically based on voltage source converters (VSC) comprising a number of series connected switching units. The switching units, comprising semiconductor switches, can be arranged in so-called PEBBs (power electronic building blocks) or so-called valve structures (also referred to as valve towers), typically placed in so-called valve halls. For a number of reasons, the PEBBs or cell stacks can be surrounded by electrically conductive structures, connected to the same or similar voltage potential as the switching units. These surrounding structures have the following possible functions:

[0003] In high voltage converters, the surrounding structures act as electric field shaping elements or corona shields. In medium voltage converters, where electric field shaping is less important, the PEBB enclosures mainly have a mechanical support function.

[0004] It is known to connect resistors between the valve structures and the corona shields, see for example WO2018 / 177515 and US2009 / 0266605, in both cases their use is related to corona discharge.

[0005] The switching events of these power semiconductors within the cells generate high frequency currents, resulting in considerable broadband electromagnetic noise. This noise can propagate outside the valve hall and can interfere with secondary electronic systems in the vicinity of the converter station, resulting in electromagnetic compatibility (EMC) problems.

[0006] The electromagnetic noise generated by the switching is typically filtered at system level by introducing filter circuits in the AC or DC field of the converter station, or by introducing high frequency damping devices in the main converter current path.

[0007] Such electromagnetic interference (EMI) filtering components are typically bulky, heavy, expensive and often require additional space. The components used in such filters need to be specially designed to meet given requirements; they are not off-the-shelf. The cost of materials and engineering can therefore also be high.

[0008] The damping devices in the main current path have to be designed to provide high frequency filtering while carrying full low frequency current. The use of magnetic material therefore requires very careful design and often requires a large core to avoid saturation at full current load.

[0009] There is therefore a need to provide improvements regarding EMI damping. SUMMARY

[0010] It is therefore an object of the present application to provide damping of electromagnetic noise in a converter arrangement without the need for additional damping or filtering equipment outside the converter arrangement.

[0011] According to a first aspect, the object is achieved by a converter arrangement comprising at least one first string of electrically interconnected modules and a first shield and a second shield, wherein the first shield is connected to a first defined electrical potential and is placed adjacent to a first group of modules in the first string comprising at least one first module, and the second shield is connected to a second defined electrical potential and is placed adjacent to a second group of modules in the first string comprising at least one second module, wherein, in operation of the converter arrangement, a resonant loop is generated from the first module via the first and second shields and the second module back to the first module, and the converter arrangement further comprises a damping unit in the resonant loop, the damping unit being arranged to damp electromagnetic noise.

[0012] Each module comprises components including switches and at least one capacitor. Further, the first defined electrical potential can be provided by a first electrical connection between the first module and the first shield, and the second defined electrical potential can be provided by a second electrical connection between the second module and the second shield. Further, the first and second shields can be placed adjacent to each other and separated by a gap defining a stray capacitance between the first and second shields.

[0013] It is apparent that the resonant loop comprises a stray capacitance and a stray inductance. Thus, the damping unit can damp electromagnetic noise in the range of 9 kHz - 6 GHz, e.g. by filtering. Thus, the damping unit can be arranged to damp or filter electromagnetic noise at frequencies defined by the stray capacitance and the stray inductance of the resonant loop.

[0014] According to a first variant, the damping unit can be a first damping unit placed between a module in said group providing the defined electrical potential and the shield provided with the electrical potential.

[0015] The group of modules can be the first group of modules, and the shield can be the first shield. In this case, the first damping unit can be placed or connected in the first electrical connection between the first module and the first shield. In a similar manner, the damping unit can also be placed in the second electrical connection between the second module and the second shield.

[0016] According to a second variant, the damping unit is placed between the first shield and the second shield. The damping unit can more specifically be connected between the first shield and the second shield.

[0017] For the damping unit placement according to the first variant, the first damping unit can be implemented using a core of a magnetic material, which core is electrically connected between a module providing a defined electric potential and a shield receiving this defined electric potential, i.e. the shield being provided with the electric potential. Furthermore, the damping unit can also comprise a coil wound on the core of the magnetic material and possibly also a resistor connected to the coil.

[0018] For the damping unit placement according to the first variant, the damping unit can comprise a filter component in the form of an inductor.

[0019] For the damping unit placement according to the second variant, the damping unit can comprise a filter component in the form of a capacitor.

[0020] The damping unit according to both variants can actually comprise a resistor. The resistor can be the only element of the damping unit. As an alternative, the damping unit can comprise an inductor and / or a capacitor. In this case, the damping unit can be a filter comprising a resistor and another filter component, wherein the resistor can be implemented using the first filter component and the other filter component, i.e. the inductor mentioned above or the capacitor mentioned above, can be the second filter component.

[0021] In case the second filter component is an inductor, the first filter component can be connected in parallel to the second filter component. This is especially the case in the first variant. In case the second filter component is a capacitor, the first filter component can be connected in series to the second filter component. This is especially the case in the second variant.

[0022] Furthermore, at least one further filter component can be present in the damping unit for providing an enhanced filtering, such as a bandpass and a bandstop filtering. Thus, the filter can comprise a plurality of components for obtaining a desired filtering function.

[0023] The shield is typically electrically conductive and can for example be made of aluminum or copper. In this case, the resistance of the damping unit can be implemented as a component, i.e. a resistor. However, as an alternative, the resistance of the damping unit can be implemented by the shield being semi-conductive. As an example, the shield can be implemented using a composite material, such as a thermoplastic or thermoset material, including an electrically conductive filler, such as carbon black. The shield can also be made of a non-conductive material with an electrically resistive coating, in which case the coating is electrically connected.

[0024] The first string can comprise a first stack and a second stack of electrically interconnected and horizontally aligned modules placed parallel to each other, wherein the first and second groups of modules are comprised in the first and second stacks, respectively. Furthermore, the first and second groups of modules can be vertically aligned with each other.

[0025] The converter arrangement can be configured to convert between alternating current, AC, and direct current, DC. In this case, the converter arrangement can comprise three strings of modules connected in three phase arms between two poles or a pole and ground, with a midpoint connected to a phase of a three phase AC system. In this case, the modules can be cells or sub-modules. In this case, the first and second shields can be corona shields provided for adjacent groups of modules in the first string, with the first and second groups of modules being two such adjacent groups.

[0026] As another example, a converter arrangement can be provided for reactive power compensation in an AC system. Thus, the converter arrangement can comprise three strings or phase arms between phases of an AC system. The strings can be connected in a delta or star between the phases. In this case, the modules can be power electronic building blocks (PEBBs). In this converter arrangement, the first and second shields are enclosures of adjacent first and second groups of modules. In this case, the shields can be enclosures or frames of PEBBs comprising a group of modules in the form of cells or sub-modules.

[0027] The invention has a number of advantages. The invention can dampen high frequency currents, so that no external filters and damping circuits are needed to reduce EMI. Furthermore, in many cases the damping cells can be placed in spaces already present in the converter arrangement, so that the size of the converter arrangement can be maintained or only slightly increased. Furthermore, the damping cells can be implemented in a simple and economic way. The damping cells are not placed in the main current path, so that they do not need to be dimensioned for high current carrying capacity (such as low Joule heating, no magnetic saturation, etc.). BRIEF DESCRIPTION OF DRAWINGS

[0028] The invention will be described below with reference to the drawings, in which

[0029] Figure 1 a phase arm of a first variant of a first type of converter arrangement and a resonant circuit occurring therein is schematically illustrated,

[0030] Figure 2 a phase arm of a first variant of a second type of converter arrangement and a resonant circuit occurring therein is schematically illustrated,

[0031] Figure 3 a resonant circuit occurring in a second variant of the first type of converter arrangement with a parallel cell stack is schematically illustrated,

[0032] Figure 4 a resonant circuit occurring in a second variant of the second type of converter arrangement with a cell string arranged in a zigzag configuration is schematically illustrated,

[0033] Figure 5a first type damping unit connected for providing EMI filtering in a first variant of a first type converter arrangement is schematically shown,

[0034] Figure 6 a first type damping unit connected for providing EMI filtering in a first variant of a second type converter arrangement is schematically shown,

[0035] Figure 7 a first type damping unit connected in a second variant of a second type converter arrangement is schematically shown,

[0036] Figure 8 a second type damping unit connected for providing EMI filtering in a first variant of a first type converter arrangement is schematically shown,

[0037] Figure 9 a second type damping unit connected for providing EMI filtering in a first variant of a second type converter arrangement is schematically shown,

[0038] Figure 10 a second type damping unit connected in a second variant of a second type converter arrangement is schematically shown,

[0039] Figure 11 an additional shielding and damping unit connected in a second variant of a first type converter arrangement with a parallel unit stack is schematically shown,

[0040] Figure 12a a first implementation of a first type damping unit is schematically shown,

[0041] Figure 12b a second implementation of a first type damping unit is schematically shown,

[0042] Figure 12c an implementation of a second type damping unit is schematically shown,

[0043] Figure 13 undamped resonance and resonance damped using a first type damping unit and a second type damping unit is schematically shown,

[0044] Figure 14 an equivalent EMI reduction circuit with a first type damping unit is schematically shown,

[0045] Figure 15 an equivalent EMI reduction circuit with a second type damping unit is schematically shown, and

[0046] Figure 16 a filter variant that can be used as a first type damping unit is schematically shown. DETAILED DESCRIPTION

[0047] The present invention relates to a converter arrangement, which can be a converter arrangement in high power applications. The converter arrangement can comprise a high voltage direct current (HVDC) converter operating at high voltages such as 80 kV and above. The converter arrangement can also be enclosed in an enclosure such as a valve hall, which has a different electrical potential compared to the different individual components of the converter arrangement. For example, when the converter arrangement is operating at a voltage level of +1500 kV or -1500 kV or some high voltage in between, the enclosure can be grounded. Other possible voltage levels are ±800 kV. The converter arrangement can for example be a converter converting between alternating current (AC) and direct current (DC), such as a voltage source converter (VSC). Furthermore, the voltage source converter can be provided as a modular multilevel converter (MMC), where a plurality of cascaded converter submodules or cells are used to form an AC waveform, where a cell comprises a switch and a capacitor. These cells can be connected in three parallel phase arms, which extend between two DC poles or between one DC pole and ground, where the midpoints of the phase arms are connected to a corresponding AC phase. This type of converter arrangement is a first type converter arrangement.

[0048] As an alternative, the converter arrangement can comprise a plurality of phase arms connected in a delta or star connection between phases of an AC system. This type of converter arrangement is a second type converter arrangement, which can be provided for reactive power compensation purposes. Also, this second type converter arrangement comprises cells or submodules comprising a switch and a capacitor, where the cells can be provided in so-called power electronic building blocks (PEBBs). More specifically, the cells are modules comprising components comprising a switch and at least one capacitor.

[0049] Figure 1 A string in a phase arm of a first variant of the first type converter arrangement 10A is schematically shown, in which a plurality of cells are connected in cascade. Here, from top to bottom, there is a first cell 12A, a second cell 14A, a third cell 16A, a fourth cell 18A, a fifth cell 20A and a sixth cell 22A, where the first cell 12A and the second cell 14A together form a first group of cells G1A, the third cell 16A and the fourth cell 18A together form a second group of cells G2A, and the fifth cell 20A and the sixth cell 22A together form a third group of cells G3A. It should be realized that the number of cells in a group can be more, but also less.

[0050] To protect different groups of cells or parts of cells from corona discharge, the first group of cells G1A is connected to a first corona shield 24A, the second group of cells G2A is connected to a second corona shield 26A, and the third group of cells G3A is connected to a third corona shield 28A. More specifically, the first corona shield 24A is placed adjacent to the first group of cells G1A, the second corona shield 26A is placed adjacent to the second group of cells G2A, and the third corona shield 28A is placed adjacent to the third group of cells G3A. The corona shields are here also shields, typically made of an electrically conductive material such as copper or aluminium. Here, the protection is typically from corona discharge from the environment, such as the walls of the valve hall, which can be kept at earth potential. The corona shields are placed at a defined potential. As an example, the second cell 14A in the first group of cells G1A has here a first electrical connection 30A to the first corona shield 24A in order to provide the first corona shield 24A with a first defined potential, the fourth cell 18A of the second group of cells G2A has a second electrical connection to the second corona shield 26A in order to provide the second corona shield 26A with a second defined potential, and the sixth cell 22A of the third group G3A has a third electrical connection to the third corona shield 28A in order to provide the third corona shield 28A with a third defined potential. In this case, the defined potential can be the potential of a particular cell in the string or a local ground. Thus, the potential can vary from cell to cell. It should be realized that another cell in the group can provide the defined potential to the corona shield instead of the second cell 14A, the fourth cell 18A and the sixth cell 22A as described.

[0051] In a similar way, Figure 2 A string in a phase arm of a first variant of the second type converter arrangement 10B is schematically illustrated, where a plurality of cells are connected in cascade. Here, from top to bottom, there is a first cell 12B, a second cell 14B, a third cell 16B, a fourth cell 18B, a fifth cell 20B and a sixth cell 22B, where the first cell 12B and the second cell 14B together form a first group of cells G1B, the third cell 16B and the fourth cell 18B together form a second group of cells G2B, and the fifth cell 20B and the sixth cell 22B together form a third group of cells G3B.

[0052] In this second type of converter device 10B, the first 12B and second 14B units are encapsulated in an enclosure in the form of a first PEBB frame 24B, the third 16B and fourth 18B units are encapsulated in an enclosure in the form of a second PEBB frame 26B, and the fifth 20B and sixth 22B units are encapsulated in an enclosure in the form of a third PEBB frame 28B. Thus, the first PEBB frame 24B is placed adjacent to and in this case also surrounding the first group of units G1B, the second PEBB frame 26B is placed adjacent to and in this case also surrounding the second group of units G2B, and the third PEBB frame 28B is placed adjacent to and in this case also surrounding the third group of units G3B. The PEBB frames are also a shield, typically made of an electrically conductive material such as copper or aluminum. The second unit 14B in the first group of units G1B has here a first electrical connection 30B to the first PEBB frame 24B in order to provide the first PEBB frame 24B with a first defined electrical potential, the fourth unit 18B of the second group of units G2B has a second electrical connection to the second PEBB frame 26B in order to provide the second PEBB frame 26B with a second defined electrical potential, and the sixth unit 22B of the third group of units G3B has a third electrical connection to the third PEBB frame 28B in order to provide the third PEBB frame 28B with a third defined electrical potential. In this case, one of these potentials can be a ground potential. It is also possible here that another unit of the group provides the PEBB frame with a defined electrical potential.

[0053] Figure 3 A second variant 10A' of the first type of converter device is shown. The unit strings of the phase legs can be placed in two parallel vertical stacks. The first 12A', second 14A' and third 16A' units discussed previously can then be placed in the first stack, while the fourth 18A', fifth 20A' and sixth 22A' units can be placed in the second stack. In this case, the first 12A', second 14A' and third 16A' units can be a first group of units G1A', while the fourth 18A', fifth 20A' and sixth 22A' units can form a second group of units G2A'. Thus, the stacks are vertically oriented and parallel to each other. The units can additionally be horizontally aligned. As Figure 3 As can be seen in the figure, the third unit 16A' can be horizontally aligned with the fourth unit 18A', the second unit 14A' can be horizontally aligned with the fifth unit 20A', and the first unit 12A' can be horizontally aligned with the sixth unit 22A'.

[0054] Figure 4A second variant of the second type of converter arrangement is shown. In this case, the first string comprises a first cell CE1, a second cell CE2, a third cell CE3, a fourth cell CE4, a fifth cell CE5, a sixth cell CE6, a seventh cell CE7, an eighth cell CE8, a ninth cell CE9, a tenth cell CE10, an eleventh cell CE11 and a twelfth cell CE12 connected in series with each other. The first cell CE1 and the second cell CE2 are enclosed in a first PEBB frame FR1, the third cell CE3 and the fourth cell CE4 are enclosed in a second PEBB frame FR2, the fifth cell CE5 and the sixth cell CE6 are enclosed in a third PEBB frame FR3, the seventh cell CE7 and the eighth cell CE8 are enclosed in a fourth PEBB frame FR4, the ninth cell CE9 and the tenth cell CE10 are enclosed in a fifth PEBB frame FR5, and the eleventh cell CE11 and the twelfth cell CE12 are enclosed in a sixth PEBB frame FR6. Here, the first cell CE1 has a first electrical connection to the first PEBB frame FR1, the third cell CE3 has a second electrical connection to the second PEBB frame FR2, the sixth cell CE6 has a third electrical connection to the third PEBB frame FR3, the eighth cell CE8 has a fourth electrical connection to the fourth PEBB frame FR4, the ninth cell CE9 has a fifth electrical connection to the fifth PEBB frame FR5, and the eleventh cell CE11 has a sixth electrical connection to the sixth PEBB frame FR6. The string has a meandering or zigzag configuration, meaning in this case that the first frame FR1 and the second frame FR2 are in a first stack, the third frame and the fourth frame are in a second stack FR3 and FR4, and the fifth frame FR5 and the sixth frame FR6 are in a third stack, these stacks being parallel to each other. Thus, the first frame FR1 is placed adjacent to the second frame FR2 and the fourth frame FR4, the second frame FR2 is placed adjacent to the first frame FR1 and the third frame FR3, the third frame FR3 is placed adjacent to the second frame FR2, the fourth frame FR4 and the sixth frame FR6, and the fourth frame FR4 is placed adjacent to the first frame FR1, the third frame FR3 and the fifth frame FR5. As a result, it is also clear here that the fifth frame FR5 is placed adjacent to the fourth frame FR4 and the sixth frame FR6, and the sixth frame FR6 is placed adjacent to the third frame FR3 and the fifth frame FR5.

[0055] In use, the above converter arrangements generate electromagnetic noise which must be removed in order to meet various electromagnetic interference (EMI) requirements. Conventionally, this EMI has been filtered at the system level by introducing filter circuits in the AC or DC field connected to the converter arrangement or by introducing high frequency damping devices in the main converter current path.

[0056] Such EMI filtering components are typically bulky, heavy, expensive, and often require additional space. Furthermore, such filters are specifically designed to meet given requirements; the components are not off-the-shelf. Thus, the cost of materials and engineering can be significant.

[0057] The damping means in the main current path must be designed to provide high frequency filtering while carrying full low frequency current. Thus, the use of magnetic material requires very careful design and often requires a large core to avoid saturation under full current load.

[0058] Therefore, there is a need for a less bulky, simpler way to achieve EMI damping.

[0059] The inventors have realized that one of the main causes of EMI in a converter arrangement is a resonant tank formed by stray inductance and stray capacitance.

[0060] There will be stray capacitance between the shields and the PEBB elements, and stray inductance between the cells in the phase arms. Thus, in Figure 1 and Figure 2 It can be seen in Figs. 1 and 2 that a first stray capacitance CSTR1A occurs between the first corona shield 24A and the second corona shield 26A, and a first stray capacitance CSRTR1B occurs between the first PEBB frame 24B and the second PEBB frame 26B. There is also a second stray capacitance CSTR2A between the second corona shield 26A and the third corona shield 28A, and a second stray capacitance CSRTR1B between the second PEBB frame 26B and the third PEBB frame 28B. Since the corona shields and the PEBB frames are shields, it can be seen that the first shield and the second shield are placed adjacent to each other and separated by a gap defining a stray capacitance therebetween, and the second shield and the third shield are placed adjacent to each other and separated by a gap defining a stray capacitance therebetween. There is also a first stray inductance LSTR1A between the first group of cells G1A and the second group of cells G2A, and a first stray inductance LSTR1B between the first group of cells G1B and the second group of cells G2B. There is also a second stray inductance LSTR2A between the second group of cells G2A and the third group of cells G3A, and a second stray inductance LSTR2B between the first group of cells G2B and the second group of cells G3B.

[0061] From Figure 3As can be seen, there is stray capacitance between cells that are vertically aligned in the two stacks. Thus, there is a third stray capacitance CSTR3A between the third cell 16A’ and the fourth cell 18A’, a fourth stray capacitance CSTR4A between the second cell 14A’ and the fifth cell 20A’, and a fifth stray capacitance CSTR5A between the first cell 12A’ and the sixth cell 22A’. There is also a stray inductance LSTR between the two stacks.

[0062] As can be seen, there is stray capacitance between cells that are vertically aligned in the two stacks. Thus, there is a third stray capacitance CSTR3A between the third cell 16A’ and the fourth cell 18A’, a fourth stray capacitance CSTR4A between the second cell 14A’ and the fifth cell 20A’, and a fifth stray capacitance CSTR5A between the first cell 12A’ and the sixth cell 22A’. There is also a stray inductance LSTR between the two stacks. Figure 4 As can be seen, there is stray capacitance between frames that are placed adjacent to each other. Thus, there is a stray capacitance C12 between the first frame FR1 and the second frame FR2, a stray capacitance C14 between the first frame FR1 and the fourth frame FR4, a stray capacitance C23 between the second frame FR2 and the third frame FR3, a stray capacitance C34 between the third frame FR3 and the fourth frame FR4, a stray capacitance C36 between the third frame FR3 and the sixth frame FR6, a stray capacitance C45 between the fourth frame FR4 and the fifth frame FR5, and a stray capacitance C56 between the fifth frame FR5 and the sixth frame FR6.

[0063] There is also stray inductance in the electrical paths between the frames. Thus, there is a stray inductance L12 between the first frame FR1 and the second frame FR2, a stray inductance L23 between the second frame FR2 and the third frame FR3, a stray inductance L34 between the third frame FR3 and the fourth frame FR4, a stray inductance L45 between the fourth frame FR4 and the fifth frame FR5, and a stray inductance L56 between the fifth frame FR5 and the sixth frame FR6.

[0064] As shown above, the surrounding structure of a PEBB or valve unit can be very large. Thus, the stray capacitance can be large. The stray capacitance can combine with the cell stray inductance (i.e., the stray inductance in the string) to form an LC resonant circuit that produces a high peak in the EMC critical frequency range, which can propagate outside the station and radiate out. Possible propagation paths include capacitive coupling to ground, inductive coupling to the busbar, etc.

[0065] As an example, as Figure 1As can be seen in Fig. 2, a first resonant loop RL is formed from the second unit 14A via the first connection 30A, the first corona shield 24, the second corona shield 26A, the fourth unit 18A and the third unit 16A back to the second unit 14A, which first loop RL comprises a first stray capacitance CSTR1A and a first stray inductance LSTR1A. As mentioned above, a unit is a module. Thus, a set of units is also a set of modules. The second unit 14A is here the first module in a first set of modules in the first resonant loop RL, while the fourth unit 18A is the second module in a second set of modules in the resonant loop RL. Thus, the first resonant loop RL is also a loop from the first module via the first and second shields and the second module back to the first module. The loop RL also passes through any modules electrically connected between the first and second modules, which in this case is the module implemented by the third unit 16A.

[0066] From Figure 2 As can be seen in Fig. 2, a first resonant loop RL is formed from the second unit 14A via the first connection 30A, the first corona shield 24, the second corona shield 26A, the fourth unit 18A and the third unit 16A back to the second unit 14A, which first loop RL comprises a first stray capacitance CSTR1A and a first stray inductance LSTR1A. As mentioned above, a unit is a module. Thus, a set of units is also a set of modules. The second unit 14A is here the first module in a first set of modules in the first resonant loop RL, while the fourth unit 18A is the second module in a second set of modules in the resonant loop RL. Thus, the first resonant loop RL is also a loop from the first module via the first and second shields and the second module back to the first module. The loop RL also passes through any modules electrically connected between the first and second modules, which in this case is the module implemented by the third unit 16A. Figure 2 As can be seen in Fig. 2, a first resonant loop RL is formed from the second unit 14A via the first connection 30A, the first corona shield 24, the second corona shield 26A, the fourth unit 18A and the third unit 16A back to the second unit 14A, which first loop RL comprises a first stray capacitance CSTR1A and a first stray inductance LSTR1A. As mentioned above, a unit is a module. Thus, a set of units is also a set of modules. The second unit 14A is here the first module in a first set of modules in the first resonant loop RL, while the fourth unit 18A is the second module in a second set of modules in the resonant loop RL. Thus, the first resonant loop RL is also a loop from the first module via the first and second shields and the second module back to the first module. The loop RL also passes through any modules electrically connected between the first and second modules, which in this case is the module implemented by the third unit 16A.

[0067] Figure 3Further, it is shown that there are multiple resonant loops through the stray capacitance and the stray inductance LSTR between vertically aligned stacks of cells. In this case, the third cell 16A' can be considered the first module of the first group of modules in the first resonant loop, and the fourth cell 18A' can be considered the second module of the second group of modules in the first resonant loop. The third cell 16A' can be considered the first module of the first group of modules in the second resonant loop, and the fifth cell 20A' can be considered the second module of the second group of modules in the second resonant loop. Finally, the first cell 12A' can be considered the first module of the first group of modules in the third resonant loop, and the sixth cell 22A' can be considered the second module of the second group of modules in the third resonant loop. Again, in this case, each loop goes through the components of any modules between the first module and the second module, and includes the stray inductance LSTR. These parallel loops can also be considered one resonant loop RL'.

[0068] Figure 4 There are also multiple resonant loops in the example of FIG. 6. There is a first resonant loop RL1 from the first cell CE1 via a first electrical connection to the first frame FR1, from the first frame FR1 via a capacitance C12 to the second frame FR2, from the second frame F2 via a second electrical connection to the third cell CE3, and from the third cell CE3 via an inductance L12 and the second cell C2 back to the first cell CE1. There is a second resonant loop RL2 from the eighth cell CE8 via a fourth electrical connection to the fourth frame FR4, from the fourth frame FR4 via a capacitance C45 to the fifth frame FR5, from the fifth frame FR5 via a fifth electrical connection to the ninth cell CE9, and from the ninth cell CE9 via an inductance L45 back to the eighth cell CE8. Finally, there is a third resonant loop RL3 from the sixth cell CE6 via a third electrical connection to the third frame FR3, from the third frame FR3 via a capacitance C36 to the sixth frame FR6, from the sixth frame FR6 via a sixth electrical connection to the eleventh cell CE11, from the eleventh cell CE11 via an inductance L56 to the tenth cell, and from the tenth cell CE10 via the ninth cell CE9, an inductance L45, the eighth cell CE8, the seventh cell CE7, and an inductance L34 back to the sixth cell CE6.

[0069] As Figure 4 As can be seen in the example of FIG. 6, a resonant loop can include more than two frames of cells. Thus, there can be cells in the frames between the two frames through which the resonant loop goes via stray capacitance. Thus, there can be more modules than the first module and the second module of the resonant loop, where these additional modules would be connected between the first module and the second module.

[0070] Aspects of the invention aim at placing local damping units in the above mentioned LC loops to obtain EMI reduction. Thus, the damping units alone can be made smaller compared to using central damping and / or filtering. These dampings can also be placed where needed for other purposes in any way. For example, a corona shield can need to have some space to the group of units it protects. If a damping unit is placed in this space, the volume of the converter arrangement remains the same with the increase of the damping unit. Thus, the damping unit does not increase the volume of the converter arrangement. The damping units can also have a simpler implementation. In some examples, the damping units can be implemented using only a resistor of appropriate size.

[0071] Thus, aspects of the disclosure aim at introducing a damping unit or dissipative element in the resonance loop to damp the resonance peak. The filtering or damping can be done in the frequency range of 9 kHz - 6 GHz, advantageously in the frequency range of 9 kHz - 2 GHz, preferably in the frequency range of 9 kHz - 1 GHz, more preferably in the frequency range of 9 kHz - 30 MHz.

[0072] This can be achieved by several measures to be discussed below.

[0073] As Figure 5 As can be seen in the first variant of the first type converter arrangement 10A, the damping is achieved by implementing a first damping unit 32A in the first resonance loop RL, ideally at a well-defined location where the unit is connected to the corona shield. The damping unit can thus be placed in the first electrical connection providing the defined potential of the first corona shield 24A, in this example, the first electrical connection 30A between the second unit 14A and the first corona shield 24A. This first damping unit 32A is connected in series with the stray capacitance CSTR1A and the stray inductance LSTR1A in the first resonance loop RL, and the damping is by the resonance in this first resonance loop RL formed by the second unit 14A, the third unit 16A and the fourth unit 18A together with the first stray inductance LSTR1A and the first stray capacitance CSTR1A. Similar damping units 34A and 36A can be connected between the fourth unit 18A and the second corona shield 26A, and between the sixth unit 22A and the third corona shield 28A, i.e. in the connections between the units and the corresponding corona shield providing the defined potential of the corona shield. The damping units are all of the first type.

[0074] As Figure 6As can be seen, in a first variant of the second type of converter device 10B, damping is achieved by implementing a first damping unit 32B in series in the loop RL, ideally at a clearly defined location where the unit is connected to the PEBB frame. Therefore, the first damping unit 32B can be placed in the first electrical connection 30B between the second unit 14B and the first PEBB frame 24B to dampen resonance in the first resonant loop RL formed by the second unit 14B, the third unit 16B, and the fourth unit 18B, as well as the first stray inductance LSTR1B and the first stray capacitance CSTR1B. Similar damping units 34B and 36B can be connected between the fourth unit 18B and the second PEBB frame 26B, and between the sixth unit 22B and the third PEBB frame 28B. All these damping units are of the first type.

[0075] like Figure 7 As can be seen, in the second variant of the second type of converter, the damping units of the first type can be connected in the same way in the connection between the unit and the frame. Therefore, the first electrical connection between the first unit CE1 and the first frame FR1 includes damping unit D1, the second electrical connection between the third unit CE3 and the second frame FR2 includes damping unit D2, the third electrical connection between the sixth unit CE6 and the third frame FR3 includes damping unit D3, the fourth electrical connection between the eighth unit CE8 and the fourth frame FR4 includes damping unit D4, the fifth electrical connection between the ninth unit CE9 and the fifth frame FR5 includes damping unit D5, and the sixth electrical connection between the eleventh unit CE11 and the sixth frame FR6 includes damping unit D6, wherein all damping units are of the first type.

[0076] The first type of damping unit can be implemented as a resistor R, such as Figure 12a As shown, or implemented as a resistor R connected in parallel with the inductor L, such as Figure 12b As shown, in the latter case, the damping unit of the first type can actually be the first filter.

[0077] Another possible placement of the damping unit is in parallel with the stray capacitance of the resonant circuit. This is as shown in the first variant of the first type of converter device disclosed. Figure 8 As can be seen, the second damping unit 38A can be connected between the first corona shield 24A and the second corona shield 26A, and it is actually connected in parallel with the first stray capacitor CSTR1A. The other damping unit 39A can be connected in a similar manner between the second corona shield 26A and the third corona shield 28A, that is, it is actually connected in parallel with the second stray capacitor CSTR2A. In this case, both damping units are of the second type.

[0078] like Figure 9As can be seen, this method can also be applied to a first variant of the second type of converter device. Therefore, the second damping unit 38B can be connected between the first PEBB frame 24B and the second PEBB frame 26B, effectively in parallel with the first stray capacitor CSTR1B. The additional damping unit 39B can be connected in a similar manner between the second PEBB frame 26B and the third PEBB frame 28B, effectively in parallel with the second stray capacitor CSTR2B. In this case, both damping units are also of the second type.

[0079] like Figure 10 As can be seen, in the second variant of the second type converter, the second type of damping unit can be connected in parallel with the stray capacitance between adjacent frames in the same manner. Therefore, there are damping units D12 connected in parallel with stray capacitance C12 between the first frame FR1 and the second frame FR2, D14 connected in parallel with stray capacitance C14 between the first frame FR1 and the fourth frame FR4, D23 connected in parallel with stray capacitance C23 between the second frame FR2 and the third frame FR3, D34 connected in parallel with stray capacitance C34 between the third frame FR3 and the fourth frame FR4, D36 connected in parallel with stray capacitance C36 between the third frame FR3 and the sixth frame FR6, D45 connected in parallel with stray capacitance C45 between the fourth frame FR4 and the fifth frame FR5, and D56 connected in parallel with stray capacitance C56 between the fifth frame FR5 and the sixth frame FR6, wherein all damping units are of the second type.

[0080] In this case, the second type of damping unit 38 can be implemented as a resistor R connected in series with the capacitor C, such as... Figure 12c As shown, in this case, the damping unit is actually a second filter.

[0081] exist Figure 11It can be seen that the damping of the resonant loop formed between the parallel stacks in the first type converter arrangement. In this case, a first vertically oriented conductive housing 42A is introduced adjacent to a first group of cells G1A' comprising cells 12A', 14A' and 16A' in the first stack, and a second vertically oriented conductive housing 44A is introduced adjacent to a second group of cells G2A' comprising cells 18A', 20A' and 22A' in the second stack. In this case, the conductive housings 42A and 44A are first and second shields, for example metal shields (made of copper or aluminum) that have already been introduced in the structure. Thus, each resonant loop extends from the first module via the first and second shields and the second module back to the first module. In this way, a well-defined stray capacitance CSTR is obtained between the two stacks. A damping cell can then be connected between the cells of the stacks and the corresponding conductive housing. This means that the resonant loop comprising the damping cells can comprise a first damping cell of the first type between the first module and the first shield, and another damping cell of the first type between the second shield and the second module. As an example, the third cell 16A' and the fourth cell 18A' are connected to the conductive housings 42A and 44A by a damping cell 48A and 52A of the first type (for example, comprising only a resistor), respectively, while the first cell 12A' and the sixth cell 22A' are connected to the conductive housings 42A and 44A by further damping cells 46A and 50A comprising a resistor in series with a capacitor, respectively. In order to avoid bypassing the first damping cell, the further damping cells typically require the capacitor to be connected to the shield. In addition, a damping cell of the second type can be connected between the two conductive housings. The further damping cells 46A and 50A can also be removed.

[0082] From Figure 13 , Figure 14 and Figure 15 The principle of damping can be understood, where Figure 13 shows an unfiltered noise curve 54, a filtered noise curve 56 using a first filter, and a filtered noise curve 58 using a second filter, Figure 14 shows an equivalent circuit of a noise source, a stray capacitance and a stray inductance, and a first type damping cell 32, and Figure 15 shows a noise source, a stray capacitance and a stray inductance, and a second type damping cell 38.

[0083] The operation of the cells in the phase leg can be seen as providing a noise source V that feeds a stray inductance LSTR in series with a stray capacitance CSTR, where the first filter 32 is connected in series with the stray capacitance CSTR in the loop, and the second filter 38 is connected in parallel with the stray capacitance CSTR in the loop. From Figure 13As can be seen, in both cases, the resonance can be significantly reduced, and thus the EMI.

[0084] As indicated above, the damping unit can be placed in the low ohmic metal connection between the unit and the shield, wherein the damping unit can be implemented by a single resistor, or by a parallel connection of discrete R and L elements (coil and resistor). The resistance value can need to be chosen so as to obtain a sufficient damping effect, while the steady state potential of the shield is not changed, and the high frequency transient potential change of the shield or enclosure does not affect the dielectric design of the station. This can be achieved with resistors in the range of 10-10 kΩ. The inductor, if present, can be in the range of 1 μ-10 mH.

[0085] The capacitor, if included, can be in the range of 1-100 nF.

[0086] It should be realized that additional components (such as additional inductors and / or capacitors) can be added to the filter to obtain enhanced filtering, such as band pass and band stop filtering.

[0087] As an alternative to the first damping unit, a core of magnetic material, such as iron or HF magnetic material (ferrite / nanocrystalline or amorphous tape) can be used instead, located on the conductor connecting the corona shield or PEBB frame with the unit. Such a core on the conductor is represented by an equivalent circuit of a parallel connection of L and R, wherein R represents the losses in the core. The optimal filter design can require more than one turn of the primary conductor, which increases the effective inductance, but reduces the maximum current at core saturation. The core can additionally comprise a secondary winding, to which a damping resistor is connected. This enables optimization of the value of the parallel R in the equivalent circuit, resulting in the optimal damping effect. The function of the secondary winding and the resistor can be implemented by a resistor and short-circuit terminals, or by a resistive coating (or potting) on the core.

[0088] Figure 16 Such a damping unit 32C with a magnetic core 60 around the first connection 30 is schematically shown, wherein a coil 62 is in turn wound around the core 60 and connected to a further resistor Rf.

[0089] The above core can additionally be formed from two halves, i.e. a ring-shaped core is cut in two halves, so that a "clip-on" application can be realized. The clip-on application is particularly useful when the conductor on which the filter RL element is to be placed cannot or can hardly be opened (disassembled). The application is thus also useful in retrofit situations.

[0090] In the above, the shield is disclosed as a metallic shield, such as an aluminum shield or a copper shield. However, it should be realized that the damping unit can also be realized by using a non-metallic corona shield element made of an electrically resistive (semi-conductive) material, e.g. a thermoplastic material comprising electrically conductive fillers like carbon black. Another alternative is to use a non-conductive shield made of e.g. a thermoplastic material, which shield has an electrically resistive coating that enables the electrical connection. In this case, the limited electrical conductivity of the shield material or shield coating introduces a resistive damping into the high frequency current path. This can also be used for damping performed by the PEBB frame.

[0091] The advantages of the present invention can be summarized as follows:

[0092] • The high frequency noise of the converter station can be significantly reduced

[0093] • The damping unit can be compact and lightweight, since the damping unit is not placed in the main current path and does not need to be dimensioned for high current carrying capacity (such as low Joule heating, no magnetic saturation, etc.)

[0094] • The material cost is low according to the compact and lightweight damping unit design

[0095] • The method can additionally potentially prevent expensive EMI design adjustments

[0096] • Only little mechanical redesign of the converter is needed, the damping unit can be designed with sufficient margin

[0097] • The method can provide a convenient and low cost solution to meet the EMI requirement after commissioning.

[0098] • The proposed method is an additional technique to control the EM noise of the converter station

[0099] From the foregoing discussion it will be apparent that the present invention can vary in a number of ways.

[0100] It should, therefore, be realized that the present invention is not limited to the particular embodiments described above, but encompasses all variations falling within the scope of the appended claims.

Claims

1. A converter device (10A; 10B) comprising at least one first string of electrically interconnected modules (12A, 14A, 16A, 18A, 20A, 22A; 12B, 14B, 16B, 18B, 20B, 22B; CE1, CE2, CE3, CE4, CE5, CE6, CE7, CE8, CE9, CE10, CE11, CE12; 12A', 14A', 16A', 18A', 20A', 22A') and first and second shields (24A, 26A; 24B, 26B; FR1, FR2; 42A, 44A), wherein, The first shield (24A; 24B; FR1; 42A) is connected to a first defined potential and placed adjacent to a first group of modules (G1A; G1B; G1A') in the first string, the first group of modules comprising at least one first module (14A; 14B; CE1; 16A'), and the second shield (26A; 26B; FR2; 44A) is connected to a second defined potential and placed adjacent to a second group of modules (G2A, G2B; G2A') in the first string, the second group of modules comprising at least one second module (18A; 18B; CE3; 18A'), wherein, in operation of the converter device, a resonant loop (RL; RL1; RL') from the first module (14A; 14B; CE1; 16A') via the first and second shields (24A, 26A, 24B, 26B; FR1; FR2; 42A, 44A) and the second module (18A, 18B, CE3; 18A') back to the first module (14A; 14B; CE1; 16A') is generated, the converter device further comprising a damping unit (32A; 32B; 32C; 38A; 38B; D1; D12; 48A) in the resonant loop, the damping unit comprising a resistance, the resistance being implemented as a resistor or by a semi-conductive shield, and the damping unit being one of a first damping unit (32A; 32B; 32C; D1; 48A) placed between a module of the group providing the defined potential and a shield (24A; 24B; FR1; 42A) provided with this potential and a second damping unit (38A; 38B; D12) connected between the first and second shields (24A, 26A; 24B, 26B; FR1, FR2), wherein the damping unit is arranged to dampen or filter electromagnetic noise at a frequency defined by a stray capacitance and a stray inductance of the resonant loop.

2. The converter device of claim 1, wherein, The first damping unit (32A; 32B; D1) comprises a filtering component in the form of an inductor.

3. The converter device of claim 1, wherein, The damping unit (38A; 38B; D12) comprises a filtering component in the form of a capacitor.

4. The converter device of claim 1, wherein, The damping unit (32C) comprises a core (60) of magnetic material surrounding a connection (30A) between a module providing a defined potential and a corresponding shield provided with this potential.

5. The converter device of claim 4, wherein, The damping unit (32C) comprises a coil (62) wound around the core of magnetic material.

6. The converter device of claim 2 or 3, wherein, In case the filtering component is an inductor, the resistance is connected in parallel with the filtering component, or in case the filtering component is a capacitor, the resistance is connected in series with the filtering component.

7. The converter device of claim 6, wherein, The damping unit comprises at least one further filtering component for providing an enhanced filtering.

8. The converter device of claim 7, wherein, The enhanced filtering is a band-pass filtering or a band-stop filtering.

9. The converter device according to any one of claims 1 to 8, wherein, The first string includes a first stack and a second stack of electrically interconnected and horizontally aligned modules placed parallel to each other, wherein the first and second groups of modules (G1A', G2A') are comprised in the first and second stacks, respectively.

10. The converter device (10A) according to any one of claims 1 to 8, wherein, The converter arrangement is configured to convert between AC and DC, and the first and second shields are corona shields provided for adjacent groups of modules in the first string.

11. The converter arrangement (10B) according to any one of claims 1 to 8, comprising three strings connected between the phases of an AC system, wherein, The first and second shields are enclosures for the adjacent first and second groups of modules.

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