Converter system
阅读说明:本技术 一种转换器系统 (Converter system ) 是由 范宝龙 于 2019-09-20 设计创作,主要内容包括:本发明公开了一种转换器系统(10)包括多个转换器单元(26),每个转换器单元(26)适于将AC单元输入电压转换为单元输出电压和变压器(18)。具有多个次级绕组(22),每个次级绕组(22)5与一个转换器单元(26)连接并提供一个转换器单元(26)的AC单元输入电压;其中,次级绕组(22)布置成至少两组(G1,G2,G3),并且连接到一组(G1,G2,G3)的转换器单元(26)串联连接;其中变压器(18)设计成使得不同组(G1,G2,G3)的次级绕组(22)提供相对于彼此相移10的AC单元输入电压,使得由转换器单元产生的更高次谐波(26)互相取消;并且其中一组(G1,G2,G3)的次级绕组(22)提供具有至少两个不同相移(θ1,θ2,θ3,θ4,θ5,θ6)的AC单元输入电压。(A converter system (10) comprises a plurality of converter cells (26), each converter cell (26) being adapted to convert an AC cell input voltage into a cell output voltage and a transformer (18). Having a plurality of secondary windings (22), each secondary winding (22) 5 being connected with one converter cell (26) and providing an AC cell input voltage of one converter cell (26), wherein the secondary windings (22) are arranged in at least two groups (G1, G2, G3) and the converter cells (26) connected to one group (G1, G2, G3) are connected in series, wherein the transformer (18) is designed such that the secondary windings (22) of different groups (G1, G2, G3) provide AC cell input voltages which are phase shifted 10 with respect to each other such that higher harmonics (26) generated by the converter cells cancel each other out, and wherein the secondary windings (22) of one group (G1, G2, G3) provide AC cell input voltages with at least two different phase shifts (θ 1, θ 2, θ 3, θ 4, θ 5, θ 6).)
1. A converter system (10) comprising: a plurality of converter cells (26), each converter cell (26) being adapted to convert an AC cell input voltage into a cell output voltage, a transformer (18) having a plurality of secondary windings (22), each secondary winding (22) being connected with one converter cell (26) and providing an AC cell input voltage of one converter cell (26), wherein the secondary windings (22) are arranged in at least two groups (Gi, G2, G3) and connected in series to the converter cells (26) of one group (Gi, G2, G3), wherein the transformer (18) is designed such that the secondary windings (22) of different groups (Gi, G2, G3) provide AC cell input voltages phase shifted with respect to each other such that higher harmonics resulting therefrom, the converter cells (26) cancel each other out, wherein the secondary windings (22) of one group (GI, G2, G3) provide AC input cells with at least two equal phase shifts (Θ 1), 02,03, θ voltage 4, 9S, θ β).
2. The converter system (10) of claim 1 wherein the secondary winding (22) of one group (Gi, G2, G3) provides an AC cell input voltage-displacement (Θ 1,02,03, θ 4, 9S, θ β) having at most two different phases in the case where K ≧ 3 converter cells (26) per group (Gi, G2, G3).
3. The converter system (10) according to claim 1 or 2, wherein each group (Gi, G2, G3) of converter cells (26) comprises at least one redundant converter cell.
4. The converter system (10) of any one of the preceding claims 1 to 3, wherein the converter system (10) comprises M groups (Gi, G2, G3) of secondary windings (22), M being an integer and the phase shift between the AC cell input voltages of the different groups being 607M.
5. The converter system (10) of claim 4, wherein the number of different phase shifts is a multiple of M.
6. The converter system (10) according to any of claims 2 to 5, wherein the phase shift between the AC cell input voltages of the secondary windings of a group (Gi, G2, G3) is 30 °.
7. The converter system (10) of one of the preceding claims, wherein each group (Gi, G2, G3) comprises two, three, four or more secondary windings (22) and converter cells (26).
8. The converter system (10) of one of the preceding claims, wherein the converter cells (26) of a group (Gi, G2, G3) are connected in series such that two directly connected converter cells (26) have the same phase shift in their AC cell input voltages.
9. The converter system (10) of one of the preceding claims, wherein the converter cells (26) of a group (Gi, G2, G3) are connected in series such that two directly connected converter cells (26) have different phase shifts in their AC cell input voltages.
10. The converter system (10) of one of the preceding claims, wherein each group (Gi, G2, G3) of series-connected converter cells (26) provides a phase (A, B, C) for the converter output voltage, and/or wherein the groups (Gi, G2, G3) of series-connected converter cells (26) are star-connected or delta-connected.
Technical Field
The present invention relates to the field of harmonic cancellation in electrical converter systems. In particular, the invention relates to a converter system with a special transformer for minimizing input harmonics, in particular when applying redundancy of converter cell stages.
Background
One particular type of converter system is the so-called cascaded H-bridge converter system, in which converter cells connected in series at their output terminals are connected at their input terminals to the secondary winding of a transformer. For example, such converter systems are used in subsea drives, wherein the converter system may be arranged subsea at sea, e.g. near a pump or the like. Such subsea systems require high reliability and long maintenance times (up to 5 to 7 years), so the use of miniaturization and redundancy of components may be one of the key issues.
When a multi-pulse transformer is used in such a cascaded H-bridge converter system, the transformer has several secondary windings providing different phase shifts, which may allow low current Total Harmonic Distortion (THD) values to be obtained.
For example, US5,625,545 and EP0913918a2 show converter systems in which converter cells of one phase are connected to a secondary winding, providing a different phase shift for each converter cell.
However, developing a multi-pulse transformer that produces a well-defined phase shift angle between the multiple three-phase systems provided on the secondary windings of the transformer may require the application of complex winding strategies (Zig-zag, Poligon, etc.). This winding strategy may result in different secondary-related short circuit impedances due to different coupling factors between the primary and secondary windings and coupling between the secondary windings. This difference in coupling factor and equivalent short circuit impedance of each secondary winding can result in ineffective harmonic cancellation on the primary side of the transformer, different DC link voltages associated with each DC link, and different harmonic currents of the DC link capacitors. These problems are therefore overcome, and become more complex as the number of secondary windings increases.
Even with a large number of converter cells and corresponding transformer secondary windings, current harmonic cancellation may be practically limited by the transformer design (coupling factor between windings, turns difference, etc.).
In addition, in the event of a failure of one of the converter cells, when redundancy of the converter cell stages is provided, the input of the converter cell may be disconnected from its corresponding transformer secondary and the output of the converter cell may be short circuited. In this case, the converter operation can continue even under nominal conditions. Also, even if the converter unit is fully operational, a unit standby strategy (N +0 operation) may be applied to minimize the total losses of the converter system and to increase the reliability of the converter system. In the case of one or more defective converter cells disconnected from the transformer, however, the number of active secondary windings of the multi-pulse transformer is reduced compared to full operation, and thus harmonic cancellation may be affected,
EP2587658a2 discloses a converter system comprising: a transformer having a plurality of secondary windings, each secondary winding being connected to one of the converter units and providing the AC unit input voltage of one of the converter units. The secondary windings are arranged in at least two groups, and the converter cells connected to one group are connected in series.
At US6,229,722B1, a universal converter system is disclosed.
Further, EP2782240a2 discloses a multilevel inverter and battery, wherein a battery switch circuit is selectively disconnected from the battery output and a bypass is closed to connect first and second battery output terminals to selectively bypass a power stage. A multi-level inverter having an optional AC input switch to selectively disconnect the AC input from the battery switch circuit during bypass.
Disclosure of Invention
It is an object of the present invention to provide a simple and robust converter system having a low THD even in case of failure of one or more converter cells and/or providing converter cell level redundancy.
This object is achieved by the subject matter of the independent claims. Further exemplary embodiments are apparent from the dependent claims and the following description.
Converter system technical field the present invention relates to a converter system, e.g. based on a cascaded H-bridge converter, connected to a multi-pulse transformer. The converter system may be
Adapted to operate subsea, may for example comprise a housing that is subjected to subsea pressure and/or is sealed against sea water. The converter system may be a medium voltage system, which may for example be adapted to handle voltages larger than 1 kV.
According to an embodiment of the invention, the converter system comprises a plurality of converter units, each converter unit being adapted to convert an AC unit input voltage into a unit output voltage, and a transformer having a plurality of secondary windings, each secondary winding being connected to one converter unit and providing the AC unit input voltage of one converter unit. Wherein the transformers are designed such that the secondary windings of the different groups provide AC unit input voltages that are phase shifted with respect to each other such that higher harmonics generated by the converter units cancel each other out.
It has to be understood that since each secondary winding is associated with one converter cell, the set of secondary windings can also be considered as a set of converter cells. These secondary winding/converter cell groups may be used to provide phases of the output voltage of the converter system, or may be connected in series to provide one output phase.
Since the converter system comprises secondary windings providing phase shifted AC converter cell voltages for different groups, the THD of the overall system can be reduced. In addition, to keep the transformer complexity down, each group of converter cells may be associated with only one phase shift or only two phase shifts relative to the other groups. Also in this case, the THD of the converter system can be reduced even in the case where the redundant unit is disconnected from the transformer.
According to one embodiment of the invention, in case of K ≧ 3 converter cells per group, the secondary windings of one group provide the AC cell input voltage with at most two different phase shifts, in order to minimize the transformer complexity despite the higher number or phase. Gear shifting may be applied.
According to an embodiment of the invention, each group of converter cells comprises at least one redundant converter cell. One or more or all converter cells in a group may be redundant, i.e. may be disconnected or connected to the group, while the converter system is still operational. Redundancy may be applied at the cell level.
In particular, the phase shift angle between different transformer secondary windings of different sets may be selected to ensure a sufficient transformer input current THD when the converter system is operated with all converter units.
Redundancy is provided at the cell level (N +1 operation), but when it is necessary to apply redundancy concepts/strategies to some non-working and/or malfunctioning converter cells over some different driving phases (N +0 operation). Furthermore, by using one or more secondary windings of a group having the same phase shift angle, the design complexity of the transformer can be minimized. This may also minimize the asymmetry between the secondary windings of the transformer in terms of short-circuit impedance.
Thus, different redundancy concepts can be applied to the converter system. For example, 1,2,3, etc. may consider each set of redundant converter cells (N +1 operation, N +2 operation, N +3 operation, etc.).
Furthermore, it is also possible to use all converter cells for normal operation (N +0 operation) to save losses in the converter and minimize stress/increase the reliability of the converter. In this case, the THD can be kept at a low level even when one or more converter units fail.
Especially for subsea drives with such converter systems, where reliability may be a critical issue, the converter system may provide redundancy of the entire rectifying-inverting stage when using modular converter units (e.g. with N +1 operational redundancy applications). At the cellular level). These modular converter units may comprise medium voltage components.
The transformer may have a primary winding and a common magnetic core for the primary and secondary windings. Since the input of the transformer at the primary winding and the output of the secondary winding may be multi-phase (in particular three-phase), the primary winding and/or the secondary winding may each have a plurality of single-phase windings.
According to an embodiment of the invention, the system comprises M groups of secondary windings, M being an integer, and the phase shift between the AC unit input voltages of different groups is 607M. In this case, the groups provide the phase of the output of the converter system, M may typically be 3 in the case of M =3, the phase shift between the AC unit input voltages of the different groups may be 20 °.
It has to be understood that in this case, when there is also a phase shift between the AC unit input voltages of a group, there may also be a phase shift between the groups other than 607M.
According to an embodiment of the invention, the number of different phase shifts is a multiple of M. When counting all possible phase shifts (independent of the group) provided by the secondary winding, there may be M, 2M, 3M, etc. Phase shifts the total number of phase shifts may be M in the case of only one phase shift per group, the number of phase shifts may be 2M in the case of two phase shifts per group.
The secondary windings of a group may have the same phase shift. As mentioned above, each group may have only one phase shift. In this case, the AC output voltages of a group are all in phase.
According to an embodiment of the invention, the phase shift between the AC unit input voltages of a set of secondary windings is 30 °. With two different phase shifts per group, there may be two types of secondary windings per group that provide AC unit input voltages that are 30 ° phase shifted between the two types.
According to an embodiment of the invention, each group comprises two, three or four secondary windings and converter cells. For medium voltage semiconductors, only a small number of converter cells per group may be used to generate the output voltage required by the medium voltage converter. Provided is a system. However, depending on the output voltage, a larger number of secondary windings and converter cells may also be applied.
In summary, the secondary windings are arranged over M sets of secondary windings (e.g., number of inverter phases M ≧ 3), where each set of secondary windings contains K secondary windings (e.g., number of converter cells K ≧ 2 per converter stage)). The number X of phase shift angles θ may be selected as a number Y (X = Y × M) in the M groups, wherein the number of phase shift angles will be assigned to each of the M secondary groups. The winding is Y (Y =1 or Y = 2). The phase shift between the secondary windings of a group may be
And the offset between adjacent secondary winding groups may be θ 1= 607M.
According to an embodiment of the invention, the converter cells of a group are connected in series such that two directly connected converter cells have the same phase shift in their AC cell input voltage. For example, in case of three converter cells per group, two adjacent converter cells may not have a phase shift, while the third converter cell is phase shifted with respect to the two adjacent converter cells. In case of four converter cells per group, there may be two pairs of adjacent converter cells, each pair of converter cells being not phase shifted, but the pairs being phase shifted.
According to an embodiment of the invention, the converter cells of a group are connected in series such that two directly connected converter cells have different phase shifts in their AC cell input voltages. For example, the converter cells of different phase shifts may alternate with respect to each other.
According to an embodiment of the invention, each group of series connected converter cells provides a phase for the converter output voltage, i.e. one end of the group may provide the output of the converter system. Furthermore, the series-connected groups of converter cells may be star-connected or delta-connected with their other end.
According to an embodiment of the invention, the series-connected groups of converter cells are connected in series to provide one output phase. It is also possible that the converter system has only one output phase AC or DC, which is generated by all converter units of all groups connected in series.
According to an embodiment of the invention, each converter cell comprises a bypass switch, for example for and/or bypassing the converter cell when the converter system fails. To provide redundancy, the converter system may disconnect each bypass converter cell from its group.
According to an embodiment of the invention, the AC unit input voltage is a multi-phase (e.g. three-phase) voltage. That is, each secondary winding may include a single winding for each phase.
Further, the AC battery output voltage may be a single phase voltage, and the converter output voltage may be a multi-phase (e.g., three-phase) voltage. The multi-phase voltage from the secondary winding may be converted by the respective converter unit into a single-phase voltage (of different frequency), which is added to one phase of the converter output voltage.
According to embodiments of the invention, each converter unit may comprise a (6-pulse) rectifier for rectifying the AC unit input voltage, each converter unit may comprise a DC-link and/or each converter unit may comprise an (H-bridge) inverter. For providing an AC battery output voltage. The converter unit may be an indirect converter unit, wherein the rectifier is connected to the secondary winding and the output may be an inverter connected in series. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
Drawings
Fig. 1 schematically shows a converter system according to an embodiment of the invention;
fig. 2 schematically shows a converter cell of the converter system of fig. 1;
fig. 3 schematically shows a converter system according to another embodiment of the invention;
FIG. 4 schematically illustrates a converter system according to another embodiment of the invention;
FIG. 5 schematically illustrates a converter system according to another embodiment of the invention;
FIG. 6 schematically illustrates a converter system according to another embodiment of the invention;
FIG. 7 schematically illustrates a converter system according to another embodiment of the invention;
fig. 8 schematically shows a converter system according to another embodiment of the invention.
In the figure: 10 converter systems, 12 inputs, 14 outputs, 16 loads, 18 transformers, 20 primary windings, 22 secondary windings, 24 secondary windings for outputs, 26 converter cells, 28 converter cell outputs, 30 cell modules, 32 cell controllers, 34 rectifiers, 36 dc links, 38 inverters, 40 disconnect switches, 42 bypass switches, a, B, C output phases, Gi, G2, G3 groups, 01,02,03,04,05,06 phase shifts.
Detailed Description
Fig. 1 shows a
The converter system comprises a three-
The
Fig. 2 shows a
To convert the AC battery input voltage from the respective secondary winding 22 into an output current, each
Furthermore, to bypass the
The
To avoid and/or minimize the above-mentioned problems of multi-pulse transformers, the
It has to be noted that the absolute phase shifts θ 1 to θ β can be provided with respect to the non-shifted (three-phase) voltage, wherein the relative phase shift between the two
In the case of fig. 1, the number of secondary windings is 12 for all output phases (in the case of N +1 operation), and 9 of them may be operable if N +0 operation is applied in all phases. Redundant operations may be applied in the following cases:
one battery fails and the
After a failure of one unit, another
One
One
3
Since the 12
Thus, the arrangement and design of the 12
Fig. 1 shows a solution in which 12
the 4
The phase shift between the 4
With this configuration of the
In addition, the phase shifts θ 1 to θ β of the 12
Fig. 1 shows only an example of how the phase shifts θ 1 to θ β are arranged to achieve the desired THD when operating in the N +1 and N +0 modes of operation.
Fig. 3 to 8 below show other configurations of the
In fig. 3, a configuration of a
The number of phase shifts can be further reduced by having only one phase shift per phase a, B, C or group Gi, G2, G3. In fig. 4, 6,8 configurations of
It has to be noted that the above discussion also applies to the groups Gi, G2, G3 of
In general, the following rules apply to all configurations shown in fig. 1 and 3 to 8:
the
Each group contains K ≧ 2
The number of phase shifts θ X is selected as a multiple Y of M groups (X = Y × M). For M =3, the number of phase shifts X is considered to be effectively limited to a maximum of X =6 in order to minimize the complexity of the transformer design and/or to minimize the short circuit impedance asymmetry between the different secondary stages.
Thus, the maximum number X of phase shifts θ X per secondary winding 22 may be practically limited to Y =1,2, although in theory Y may be a higher integer value, as long as the transformer complexity and its meaning is affordable.
The number of phase shifts θ x assigned to each of the M groups of
The phase shift between adjacent secondary winding
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or controller or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.
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