Medium-pressure speed change assembly

Abstract

A medium voltage speed change assembly comprises an electric machine (2) and a power supply arrangement for providing alternating current power to the electric machine (2). The electric machine comprises a plurality of stator winding systems (4). The power supply arrangement comprises a power converter system (6) having a two-level direct current input (61) and an alternating current output (62) connected to a plurality of stator winding systems (4). The power converter system (6) comprises a plurality of converter devices (8) connected in series such that each converter device (8) comprises at least one two-level converter cell having a DC link whose nominal voltage is sufficiently low for an IGBT, MOSFET or similar component. Characteristics of the electric machine, such as the number of machine phases, the number of stator poles, the number of stator winding systems, and the number of stator slots, are selected in a particular manner.

Description

Technical Field

[0001] The present invention relates to a medium voltage variable speed assembly including a rotating electric machine and a power supply arrangement for supplying alternating current power to the machine. Background Art

[0002] The torque and power of an electric machine are associated with the rotor volume. This leads to maximizing the rotor diameter and length in the design and correspondingly minimizing the height of the stator yoke. A common formula for electric machine power production is:

[0003] P mec = C mec ·D 2 ·L·n syn

[0004] Where C mec represents the machine constant, D represents the rotor diameter, L represents the equivalent stack length, and n syn represents the rotor synchronous speed.

[0005] Since maximizing the rotor volume is advantageous, the first limiting factor comes from the space reserved for the magnetic flux. Electrical steel sheets can use a magnetic flux density of up to about 1.2 tesla without severe saturation. If the magnetic flux density is much higher, the required magnetization current increases but the torque is not increased. Due to this magnetic flux density limitation, the machine is designed such that the stator or rotor yoke does not saturate severely. The magnetic flux density in the stator (or rotor) yoke also depends on the number of poles of the machine. If there are only two poles in the machine, the flux needs to flow back to the air gap after half a cycle of the machine. For a higher number of poles, the same air gap flux is more evenly distributed around the yoke. As a result, when the number of poles increases, the required thickness of the stator yoke decreases.

[0006] When the number of poles increases, the required thicknesses of the stator and rotor yokes decrease significantly. In fact, compared to a two-pole machine, a four-pole machine has a larger rotor diameter but a smaller stator outer diameter. In practice, this makes the machine design smaller and thus more cost-effective.

[0007] If the speed of the shaft system is controlled by a variable speed drive (VSD), it is very beneficial, or even mandatory, to allow continuous operation at any speed between zero and the nominal speed (also known as sub-critical operation). Unfortunately, the mechanical structure of the electric machine often limits the operating speed range of the system. These limitations affect the sub-critical design in two ways; due to rotor bending modes and frame modes.

[0008] The rotor bending mode mainly depends on the bearing span of the system, the weight of the rotor core, and the diameter of the shaft. In a two-pole machine, the diameter of the rotor core is limited due to the thickness of the stator yoke. In addition, the length of the rotor core is limited due to the space reserved for the long stator coil ends. These factors reduce the volume of the rotor and further increase the weight of the core. Ultimately, the first bending mode appears at a higher frequency, but the same factors also reduce the torque of the machine. If the number of poles is increased, the rotor diameter can be increased while the stator yoke becomes thinner. This not only increases the torque generation but also increases the weight of the core. Initially, the motor generates greater torque, but the first bending mode limits the nominal speed to a value lower than that of a two-pole machine. However, this drawback can also be compensated for by considering the dimensions of the rotor yoke. As the number of poles increases, the required thickness of the rotor yoke also decreases. For a thinner yoke, a larger shaft diameter can be used. Therefore, the rotor can be designed such that the first bending mode appears at a higher frequency than in a two-pole design. In summary, by using the optimal number of poles, the machine can generate greater torque for the same frame size without sacrificing rotor dynamic characteristics, such as maintaining the same operating speed range.

[0009] The number of poles of the machine also affects the exciting force caused by the radial air-gap flux. Especially in a two-pole machine, the radial flux generates a force on the inner diameter of the stator, which rotates at twice the line frequency.

[0010] This force can excite the mechanical modes of the static structure, such as the overall mode of the machine. The most problematic mode shape that this force can excite is the horizontal mode of the frame, as Figure 1 shown.

[0011] The nominal frequency of the horizontal mode depends on the size and weight of the machine. Therefore, the only viable solution to solve the vibration is to reduce the exciting force from the stator to the frame. In a two-pole machine, common solutions are to increase the stator yoke thickness and reduce the air-gap flux density. Both have a negative impact on the power density of the machine, as well as its size and cost.

[0012] A more fundamental solution to avoid vibration problems caused by mechanical mode shapes and critical speed limitations is to reduce the harmful exciting modes in the stator core. The air-gap force has different shapes between two- and four-pole designs. The number and frequency of the symmetrically rotating force components on the inner surface of the stator directly depend on the number of poles of the machine and the supply frequency. Therefore, if the number of poles is higher, the component forces caused by the air-gap flux also affect a smaller area. Since the exciting force acts on a narrower stator region, the overall mode of the entire structure is not excited. It can also be generalized that if the number of poles of a large motor with a modular steel frame is high enough, the lowest mechanical mode shape of the frame appears at a frequency much lower than the frequency of the exciting force caused by the main stator flux.

[0013] In summary, the number of poles of a VSD-powered motor should be based on specific application requirements rather than selecting a standard direct-online machine as the basic design, for several reasons:

[0014] · Motors with the optimal number of poles are smaller and more cost-effective.

[0015] · Motors with the optimal number of poles have a wider sub-critical operating range.

[0016] · Motors with the optimal number of poles can be designed such that the excitation force caused by the stator main flux does not have a corresponding mechanical mode shape, resulting in low vibration of the structure.

[0017] In high-power applications, the end user connects a direct-online motor to a medium-voltage power grid. This medium-voltage power grid typically operates between 4.16 kV and 13.2 kV. If speed control is required for the application, it would be beneficial to connect these speed-controlled machines to the same power grid. This means that the VSD must also operate at a medium-voltage level. Of course, a higher voltage level also reduces the wiring cost of the system.

[0018] The traditional solution for high-power medium-voltage VSD applications is to manufacture converters with integrated gate-commutated thyristors (IGCTs) or similar thyristor-based semiconductors to withstand high voltages. Unfortunately, these thyristor-based semiconductors typically operate with high switching losses. Due to the high switching losses, the switching frequency must be much smaller than that of converters based on insulated gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs). The low switching frequency also limits the maximum output frequency of the converter because the number of switches per fundamental period should be high enough, typically more than 15, to achieve precise control. Figure 2 and Figure 3 shows an ICGT-based NPC topology converter. In both cases, an independent block transformer with multiple secondary coils is required. From the perspective of the machine, the high total harmonic distortion (THD) of the inverter output voltage and the limited output frequency reduce the performance of the machine.

[0019] To address the problems caused by the high switching losses of thyristor-based components, the industry has developed different types of multilevel inverter modules. Using this approach, transistor-based semiconductors (IGBTs) are used instead of thyristors. However, this requires the system to have multiple DC levels and thus a more complex rectifier unit. For example, in practice, the cascaded H-bridge can only be used for special transformers with multiple secondary windings. A large number of secondary windings forces the transformer to be integrated near the converter unit, otherwise the wiring cost would be too high. Although the motor design can be more optimized, both the system complexity and cost increase. Additional limitations come from the series connection of components, and these configurations do not scale well to multi-phase configurations.Figure 4 and Figure 5 shows some of the most common medium - voltage converter configurations made of IGBT components.

[0020] Figure 4 shows a known five - level active neutral - point clamped (ANPC) VSD assembly with IGBT components. Figure 5 shows a known cascaded H - bridge with IGBT modules and a special transformer. In Figure 5 it, the power units are denoted by the reference symbols A1 - A6, B1 - B6, and C1 - C6. Figure 5 The power units shown are IGBT modules.

[0021] As described above, the number of poles has a significant impact on the size and performance of the machine. However, since the number of poles directly affects the supply frequency of the machine, existing VSD technologies limit the optimization of the motor. Due to the output frequency limitation caused by thyristor - based semiconductors, the motor must use a non - optimal number of poles, which further reduces the motor utilization rate and ultimately increases the motor cost. Multilevel converters using IGBT components can enable a more optimized machine design, but the complex converter structure often leads to a higher system cost and lower overall efficiency.

[0022] When a medium - voltage direct - on - line (DOL) motor is compared with a VSD system, the end - user not only needs to consider the additional losses and the cost of a separate block transformer, but also the space and ventilation required. Especially in the case where the customer has a medium - voltage distribution network such as 6.6 kV, the installation cost of a medium - power (<2 MW) variable - speed drive can be several times higher than the installation cost of using only a medium - voltage DOL motor. Summary of the Invention

[0023] The object of the present invention is to provide a medium - voltage variable - speed assembly optimized for a specific speed and power. The object of the present invention is achieved by the following medium - voltage variable - speed assembly.

[0024] The present invention is based on the following ideas: providing an assembly motor with a plurality of stator winding systems; providing a power supply configuration of the assembly with a plurality of converter devices connected in series, such that each converter device in the converter devices includes at least one two - level converter unit having a DC link, and the nominal voltage of the DC link is low enough for IGBTs, MOSFETs, or similar components; and selecting the number of machine phases, the number of stator winding systems, the number of groups of stator winding systems, the number of stator poles, the number of stator poles connected in series in each stator winding system, and the number of stator slots in a specific manner.

[0025] The advantages of the medium-voltage variable-speed component of the present invention are that when the DC input of the power converter system is a two-level input, the rotor volume of the motor of the component and the torque per volume are maximized. The motor of the component is optimized and not limited by the nominal frequency. The converter unit of the power converter system is realized by controllable switches with a relatively low nominal voltage, such as IGBTs, MOSFETs or similar components. The power configuration of the component can realize a grid converter system, for example, through a six-pulse configuration with passive semiconductors (such as diodes). A bulky transformer is not required, thus avoiding transformer losses.

[0026] The present invention reduces the mechanical stress in the motor during a short circuit of the power converter system. If a single converter unit fails and eventually a short circuit occurs, only a single winding system is short-circuited, and the force caused by the short-circuit current is reduced compared to a complete short circuit of all stator windings.

[0027] In the medium-voltage variable-speed component of the present invention, by selecting the dimensions of the magnetic circuit, the motor is optimized for a specific speed and power, such that the rotor volume is maximized while the frame size is minimized. Part of this optimization process is to select the number of poles of the motor without restricting the nominal frequency of the machine. This can be achieved by dividing the stator windings of the motor into independent winding systems, which are powered by a power converter system realized by controllable semiconductor switches with a high switching frequency and output frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Hereinafter, the present invention will be described in more detail by way of preferred embodiments with reference to the accompanying drawings, wherein

[0029] Figure 1 shows a typical mechanical mode shape of a motor with a modular frame;

[0030] Figure 2 shows a known typical medium-voltage converter with an NPC topology;

[0031] Figure 3 shows a known medium-voltage frequency converter with an NPC converter module in an H-bridge;

[0032] Figure 4 shows a known VSD component with a five-level ANPC topology;

[0033] Figure 5 shows a known cascaded H-bridge with IGBT modules and a special transformer;

[0034] Figure 6 shows a connection diagram of a medium-voltage variable-speed component according to an embodiment of the present invention;

[0035] Figure 7Shows a connection diagram of a medium-voltage variable-speed assembly according to another embodiment of the present invention; and

[0036] Figure 8 Shows a connection diagram of a medium-voltage variable-speed assembly according to another embodiment of the present invention. Detailed Description

[0037] Figure 6 Shows a connection diagram of a medium-voltage variable-speed assembly, which includes a motor 2, a power supply configuration for supplying AC power to the motor 2, and a controller 909 for controlling the power supply configuration. Here, the medium-voltage variable-speed assembly refers to an assembly whose nominal voltage of the assembly motor is in the range of 1 kV to 35 kV.

[0038] The motor 2 is a rotating motor including six poles and six stator winding systems 4. Each stator winding system 4 is a three-phase system isolated from the ground and other stator winding systems 4. The power supply configuration includes a grid converter system 5 and a power converter system 6.

[0039] In one embodiment, each stator winding system includes two layers of diamond coils.

[0040] The grid converter system 5 has an AC input 51 and a DC output 52. The AC input 51 is adapted to be electrically connected to a three-phase medium-voltage grid. In Figure 6 this case, the AC input 51 is electrochemically connected to the three-phase medium-voltage grid.

[0041] The nominal voltage of the AC input 51 of the grid converter system 5 is 5.6 kV. In an alternative embodiment, the nominal voltage of the AC input of the grid converter system is in the range of 4 kV to 15 kV. The grid converter system 5 has a six-pulse configuration implemented by six diodes. In another alternative embodiment, the grid converter system has a six-pulse configuration with other passive semiconductors.

[0042] The power converter system 6 has a DC input 61 and an AC output 62. The DC input 61 is electrically connected to the DC output 52 of the grid converter system 5. The AC output 62 is electrically connected to the stator winding system 4.

[0043] The DC input 61 of the power supply conversion system 6 is a two-level input, such that the grid converter system 5 is electrically connected to the power converter system 6 only through two busbars (i.e., the positive busbar and the negative busbar). The power converter system 6 includes six series-connected converter devices 8. The voltage across the six series-connected converter devices 8 is equal to the voltage between the positive busbar and the negative busbar.

[0044] Each converter device 8 includes exactly one converter unit 82 and is adapted to supply AC power to exactly one stator winding system 4. In an alternative embodiment, the number of multiple stator winding systems is a multiple of the number of converter devices.

[0045] The controller 909 is adapted to control the converter devices 8 such that they are in phase with each other, so that there is no phase shift between the different converter devices 8. In an alternative embodiment, the power converter system comprises a plurality of converter devices connected in series, wherein the plurality of converter devices comprises a plurality of groups of converter devices such that there is a phase shift between different groups of converter devices. Each group of converter devices has the same number of converter devices.

[0046] Each converter device 8 comprises a capacitor system electrically connected to the DC input of the converter device 8. Each capacitor system has only one capacitor C1. In an alternative embodiment, each capacitor system comprises at least one capacitor.

[0047] Each converter unit 82 is a two-level converter unit and comprises a three-phase output electrically connected to exactly one stator winding system 4. Here, the two-level converter is a converter implemented by a six-pulse bridge. Each converter unit 82 comprises six controllable switches which are adapted to supply AC power to exactly one stator winding system 4. Each controllable switch is an insulated gate bipolar transistor (IGBT).

[0048] In an alternative embodiment, the controllable switches of each converter unit in the plurality of converter devices comprise insulated gate bipolar transistors, metal oxide semiconductor field effect transistors (MOSFETs) or similar components having low switching losses and high switching frequencies. In said alternative embodiment, the switching frequency of the controllable switches of each converter unit is greater than or equal to 750 Hz.

[0049] The medium voltage variable speed assembly according to the invention is designed such that the parameter q defined by the formula

[0050]

[0051] is the number of stator slots per pole per phase, where Q s is the number of stator slots in the motor (2), p is the number of pole pairs in the motor (2), and c p is the number of groups of stator winding systems, where in embodiments where c p is greater than or equal to 2, c p gives a plurality of stator winding systems having a phase shift relative to each other in each stator pole. The phase shift between two consecutive groups of stator winding systems is 60° / c p . Thus, the number of phases in the motor of the medium voltage variable speed assembly according to the invention is equal to 3c p . Further, the number n c of converter devices connected in series in the power converter system and the number k spand the number k of stator poles connected in parallel in each stator winding pp meet the requirements

[0052] n c k sp k pp = 2pc p and the product qk sp is an integer.

[0053] Refer to Figure 6 the illustrated embodiment, where p = 3, c p = 1, n c = 6, k pp = 1, k sp = 1. Therefore, the number Q of stator slots s can be selected as a multiple of 18, or a multiple of any one of them.

[0054] Figure 6 There are six stator winding systems 4 in the medium voltage variable speed assembly shown. For Figure 6 the assembly, c p is selected to be 2, and the assembly is a six-phase assembly. In a six-phase assembly, there are two groups of stator winding systems with a phase shift of 60 / c p between them, which is equal to 30. It should be noted that by only configuring the controller 909, values 1, 2, and 3 can be selected for c Figure 6 in the assembly shown. If the stator windings are connected accordingly, no modification to the hardware of the power converter system 6 is required. p

[0055] Due to the maximum voltage of currently available IGBTs, the number n Figure 6 of converter devices connected in series in the power converter system 6 c is selected such that the nominal DC link voltage of each converter unit is less than 1700V. The nominal voltage U tot at the DC input 61 of the power converter system 6is the sum of the nominal voltages of the DC links of the converter units 82. In an alternative embodiment, each converter unit in the plurality of converter devices is a two-level converter unit and has a DC link with a nominal voltage less than or equal to 2 kV.

[0056] In the case of c p = 3, 2p = 6, k sp = 1 and k ppIn the embodiment where c

[0057] = 3, 2p = 6, k p = 3 and k sp = 1, there are a total of eighteen stator winding systems, and there is a 20° phase shift between the first stator winding system group and the second stator winding system group, and between the second stator winding system group and the third stator winding system group. The assembly includes eighteen converter devices in three converter device groups, and there is a 20° phase shift between the first converter device group and the second converter device group, and between the second converter device group and the third converter device group. pp = 1, there are a total of six stator winding systems, and there is a 20° phase shift between the first stator winding system group and the second stator winding system group, and between the second stator winding system group and the third stator winding system group. The assembly includes six converter devices in three converter device groups, and there is a 20° phase shift between the first converter device group and the second converter device group, and between the second converter device group and the third converter device group.

[0058] Figure 7 A connection diagram of a medium-voltage variable-speed assembly is shown, and this assembly is Figure 6 an improvement of the assembly shown. Figure 7 The medium-voltage variable-speed assembly of

[0059] includes a motor 2', a power supply configuration for supplying AC power to the motor 2', and a controller 909' for controlling the power supply configuration.

[0060] The motor 2' is a rotating motor including three stator winding systems 4'. Each stator winding system 4' is a three-phase system isolated from the ground and other stator winding systems 4'. The power supply configuration includes a grid converter system 5' and a power converter system 6'.

[0061] The grid converter system 5' is the same as the grid converter system 5. The power converter system 6' has a DC input 61' and an AC output 62'. The DC input 61' is electrically connected to the DC output 52' of the grid conversion system 5'. The AC output 62' is electrically connected to the stator winding system 4'.

[0062] The controller 909' is adapted to control the converter devices 8' such that they are coplanar with each other.

[0063] Each converter device 8' includes a capacitor system electrically connected to the DC input of each converter device 8'. Each capacitor system has two capacitors C1', one corresponding to each of the parallel converter units 82'. In an alternative embodiment, the capacitor system includes only one capacitor, and the converter device includes a plurality of parallel converter units.

[0064] Each converter unit 82' is identical to converter unit 82. Each converter device 8' includes a three-phase output that is electrically connected to exactly one stator winding system 4'. The two parallel-connected converter units 82' of each converter device 8' are adapted to supply AC power to the same stator winding system 4'.

[0065] Figure 8 A connection diagram of a medium-voltage variable-speed assembly is shown, which is Figure 6 Another variant of the assembly shown. Figure 8 The medium-voltage variable-speed assembly includes a motor 2”, a power supply configuration for supplying AC power to the motor 2”, and a controller 909” for controlling the power supply configuration.

[0066] The motor 2” is a rotating motor including six stator winding systems 4”. Each stator winding system 4” is a three-phase system isolated from ground and other stator winding systems 4”. The power supply configuration includes a grid converter system 5” and a power converter system 6”.

[0067] The grid converter system 5” is identical to the grid converter system 5. The power converter system 6” has a DC input 61” and an AC output 62”. The DC input 61” is electrically connected to the DC output 52” of the grid conversion system 5”. The AC output 62” is electrically connected to the stator winding system 4”.

[0068] The DC input 61” of the power converter system 6” is a two-level input. The power converter system 6” includes three series-connected converter devices 8”. Each converter device 8” includes two parallel-connected converter units 82”, and is adapted to supply AC power to two stator winding systems 4”, such that the two parallel-connected converter units 82” are adapted to supply AC power to different stator winding systems 4”. Each converter unit 82” is suitable for supplying AC power to exactly one stator winding system 4”.

[0069] The controller 909” is adapted to control the converter values 8” in the same way such that there is a phase shift between the two parallel-connected converter units 82” of each converter device 8”. Each converter unit 82” is identical to converter unit 82.

[0070] Each converter device 8" includes a capacitor system electrically connected to the DC input of each converter device 8". Each capacitor system has two capacitors C1", one corresponding to each parallel converter unit 82".

[0071] In c p = 3, 2p = 6, k sp = 1 and k pp = 3 embodiment, there are a total of six stator winding systems, with a 20° phase shift between the first stator winding system group and the second stator winding system group, and between the second stator winding system group and the third stator winding system group. The assembly includes three converter devices, each having two converter units. There is a 20° phase shift between the first converter device and the second converter device, and between the second converter device and the third converter device.

[0072] In c p = 3, 2p = 6, k sp = 1 and k pp = 2 another embodiment, there are a total of six stator winding systems, with a 30° phase shift between the first stator winding system group and the second stator winding system group. The assembly includes two converter devices, each having three converter units, with a 30° phase shift between the first converter device and the second converter device.

[0073] The following table illustrates how to configure a six-pole motor for a medium-voltage power grid with different voltage levels while maintaining the same speed and power rating of the motor. In this table, U g is the nominal voltage of the medium-voltage power grid, U tot is the nominal voltage at the DC input of the power conversion system, n c is the number of converter devices connected in series in the power conversion system, U ca is the nominal voltage of the DC link in each conversion unit of the plurality of conversion devices, 3c p is the number of phases in the six-pole motor, c is the number of stator poles connected in series in each stator winding system, k pp is the number of stator poles connected in parallel in each stator winding system, Q s is the number of stator slots in the motor.

[0074] <![CDATA[U g [kV]]]> <![CDATA[U tot [kV]]]> <![CDATA[n c > <![CDATA[U ca [kV]]]> <![CDATA[3c p > <![CDATA[3c p > <![CDATA[k pp > <![CDATA[Q s > 4.16 5.6 6 940 3 1 1 Multiples of 18 6.6 8.9 9 990 9 2 1 Multiples of 27 13.2 17.8 18 990 9 1 1 Multiples of 54

[0075] The stator winding systems are placed in the stator slots in a known manner not described in this agreement.

[0076] It will be apparent to those skilled in the art that the concepts of the present invention can be implemented in various ways. The present invention and its embodiments are not limited to the above examples, but may vary within the scope of the claims.

Claims

1. A medium voltage transmission assembly, comprising: An electric machine (2), the electric machine (2) being a rotating electric machine comprising a plurality of stator winding systems (4), wherein each of the stator winding systems (4) is a three-phase system; and A power supply arrangement for providing AC power to the motor (2), wherein the power supply arrangement comprises a power converter system (6), the power converter system (6) having a DC input (61) and an AC output (62) connected to the plurality of stator winding systems (4), wherein the power converter system (6) comprises a plurality of converter devices (8) connected in series, and each converter device of the plurality of converter devices (8) comprises at least one converter unit (82) and is adapted to provide AC power to at least one stator winding system of the plurality of stator winding systems (4), It is characterized in that The DC input (61) of the power converter system (6) is a two-level input; Each converter unit (82) of the plurality of converter devices (8) is a two-level converter unit and has a DC link with a nominal voltage less than or equal to 2 kV; The number of stator winding systems (4) is greater than or equal to the number of converter devices (8), wherein each of the converter units (82) is adapted to provide AC power to exactly one stator winding system (4); Each of the stator winding systems (4) is isolated from the ground and from other stator winding systems (4); By formula The parameter q is defined as the number of stator slots per phase and per pole, where Q s is the number of stator slots in the motor (2), p is the number of pole pairs in the motor (2), and c p is the number of stator winding system groups, The number n of converter devices (8) connected in series in the power converter system (6) is c and the number k of stator poles connected in series in each stator winding system sp and the number k of stator poles connected in parallel in each stator winding pp Meet the requirements c k sp k pp =2pc p And accumulate qk sp is an integer.

2. A medium voltage speed change component according to claim 1, wherein the component includes a controller (909), the controller (909) being used to control the power supply configuration so that the switching frequency of the controllable switch of each converter unit (82) is greater than or equal to 750 Hz, wherein the controllable switch is suitable for providing AC power to the multiple stator winding systems (4).

3. A medium voltage transmission assembly according to claim 1 or 2, wherein the controllable switch of each converter unit (82) of the plurality of converter devices (8) comprises an insulated gate bipolar transistor and / or a metal oxide semiconductor field effect transistor, wherein the controllable switch is suitable for providing AC power to the plurality of stator winding systems (4).

4. The medium voltage transmission assembly according to claim 1, wherein the nominal voltage of the DC input of the power converter system (6) is Among them U g In the range of 4kV to 15kV.

5. A medium voltage speed change assembly according to claim 1, wherein the power supply configuration includes a grid converter system (5), the grid converter system (5) having an AC input and a DC output, the AC input being suitable for being electrically connected to a three-phase grid, and the DC output being connected to the DC input of the power converter system (6).

6. The medium voltage transmission assembly according to claim 5, wherein the grid converter system (5) has a six-pulse configuration with passive semiconductors.

7. The medium voltage transmission assembly according to claim 5, wherein the nominal voltage (U g ) is in the range of 4kV to 15kV.

8. The medium voltage transmission assembly according to claim 1, wherein each converter device of the plurality of converter devices (8) comprises a capacitor system, the capacitor system being electrically connected to a DC input of the each converter device, wherein the capacitor system comprises at least one capacitor.

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