DE112009002287T5 - Modular multipulse transformer Rectifier for use in multi-level power converters - Google Patents

Abstract

In one embodiment, a system may include a plurality of transformers each providing an output to one or more power cells, wherein the power cells of a load provide AC power. Each transformer may include at least one primary winding and a plurality of secondary windings, the primary winding of each transformer being out of phase with respect to its adjacent transformers, and the secondary windings also being out of phase. The phase shift of the primary winding may be based on the phase shift of the secondary windings and a number of the plurality of transformers.

Description

background

Generally, a resource referred to as a power converter, inverter, or driver is used to provide power to another resource, such as a motor. In particular, such a converter (converter is commonly used herein to refer to converters, inverters, and drivers) is coupled to a supply terminal to receive incoming power, such as three-phase AC power. The converter recycles the power so that a conditioned power signal is provided to the resource to which power is to be provided. As a result, incoming power to the resource may have improved efficiency, resulting in reduced costs in operating the equipment.

Multi-level power converters have gained popularity mainly due to improved power quality, lower switching losses, better electromagnetic compatibility, and higher voltage capability. These improvements in power conversion are achieved by using a multiple voltage step strategy. A common multi-level inverter topology is a series H-bridge inverter in which multiple H-bridge inverters are connected in series. Because this topology consists of series power conversion cells, the voltage and power levels can be easily scaled.

However, this topology requires a large number of isolated DC power sources to power each cell. The common practice is to use an isolation transformer to power a rectifier of a power cell. However, the supply current to the rectifier contains many harmonic current components that are very troublesome to a resource and power systems and cause electromagnetic interference (EMI).

Some systems use a single stage transformer with multiple phase shifted secondary windings. However, deleting harmonics in a single-stage transformer can not be optimized. The main obstacle is the manufacturing process and a lower degree of freedom due to fewer turns, which makes it very difficult to implement small phase shift angles required for efficient and optimized cancellation of harmonics.

Summary of the invention

In one aspect, the present invention is directed to a medium voltage drive system that includes modular transformers. The system may include a plurality of transformers, each providing an output for one or more power cells, wherein the power cells provide AC power to a load. Each transformer may have at least one primary winding and a plurality of secondary windings, the primary winding of each transformer being phase shifted with respect to its neighboring transformers, and the secondary windings also being out of phase. In one implementation, the phase shift of the primary winding is based on the phase shift of the secondary windings and a number of the plurality of transformers. For example, there may be three modular transformers, and the system acts as a 54-pulse transformer. In some implementations, in addition to the phase-shifted transformers, one or more non-phase-shifted transformers may also be present to provide at least one power cell with an output.

Another aspect of the present invention is directed to a system having a plurality of modular transformers, each of which includes at least one out-of-phase primary set of windings for receiving power from a supply terminal and comprising a plurality of secondary sets of windings. In addition, the system includes power cells, each of which is coupled to one of the secondary sets of windings of one of the modular transformers. The power cells are configured such that a first subset of the power cells is coupled to a first phase output line, a second subset of the power cells is coupled to a second phase output line, and a third subset of the power cells is coupled to a third phase output line. Each modular transformer provides output to a first number of power cells of a pair of the three phase output lines and a second number of power cells of a last one of the phase output lines. Furthermore, any of the power cells may be coupled to any of the secondary sets of windings of any of the modular transformers.

In one implementation, each transformer provides the output to the first number of power cells from another pair of the three phase output lines. For example, a first modular transformer of a first power cell of the first and second phase output lines and provide two power cells of the third phase output line outputs.

Yet another aspect of the present invention is directed to a system having multiple transformers, each of which provides an output for at least one power cell coupled to at least one phase output line and configured to provide AC power to a load. Each transformer may include at least one primary winding and a plurality of secondary windings, the primary winding of each transformer being phase shifted with respect to its adjacent transformers, and the secondary windings being out of phase with the other secondary windings of the corresponding transformer. In addition, the system further includes a non-phase-shifted transformer that provides output to at least a second power cell. Such second power cell (s) may be configured to partially regenerate the load. For this purpose, the second power cell (s) include an active input coupled to an output of its corresponding secondary winding (s). A controller may be coupled to at least one of the second power cell (s) to control switching of the active input.

In one aspect, the present invention is directed to a drive system that includes modular transformers. The system may include a plurality of modular transformers, each including a phase-shifted primary winding coupled to an input power source, and phase-shifted secondary windings, each of which is connected to a power cell. The system further includes various phase output lines coupled to a load. These lines may include first, second and third phase output lines. The first phase output line may include at least first and second level power cells, wherein a first of the modular transformers includes a first plurality of the phase shifted secondary windings coupled to the first level power cells and a second plurality of the phase shifted secondary windings connected to the second level power cell are coupled. Likewise, the second phase output line may include at least first and second level power cells, a second one of the modular transformers having a first plurality of the phase shifted secondary windings coupled to the first level power cell and a second plurality of the second phase shifted windings second to the power cell Levels are coupled. The third phase output line may in turn comprise at least first and second level power cells, a third of the modular transformers having a first plurality of the phase shifted secondary windings coupled to the first level power cell and a second plurality of the phase shifted secondary windings second to the power cell Levels are coupled.

In some implementations, the first phase output line may include a third level power cell, wherein at least one of the phase shifted secondary windings of the first modular transformer is coupled to the third level power cell. The power cells of different levels may be of different voltages, wherein the power cell is first level of a higher voltage than the second level power cell and the second level power cell is of a higher voltage than the third level power cell. Each modular transformer can be of the same level of expenditure.

In another aspect, the present invention includes a device having a plurality of modular transformers, each of which includes at least one out-of-phase primary set of windings to receive power from a supply port, and a plurality of secondary sets of windings. In addition, there may be power cells of multiple levels, the first level power cells each coupled to a first plurality of secondary sets of windings of at least two of the modular transformers, and the second level power cells each having a second plurality of secondary sets of windings of at least two of the modular ones Transformers are coupled. In some implementations, any of the first level and second level power cells may be coupled to any one of the secondary sets of windings of any one of the modular transformers.

In yet another aspect, a system includes a plurality of modular transformers. A first modular transformer includes at least one phase-shifted primary winding to be coupled to a supply and phase-shifted secondary windings, each for coupling to a third-level power cell. A plurality of second modular transformers each include at least one phase-shifted primary winding for coupling to the supply and phase-shifted secondary windings each for coupling to a second level power cell. Several of the phase-shifted secondary windings of the second modular transformers are intended to be connected to the same second-level power cell couple. A plurality of third modular transformers each include at least one phase-shifted primary winding coupled to the supply and phase-shifted secondary windings each for coupling to a first level power cell. The system may be implemented such that a plurality of phase-shifted secondary windings of the third modular transformers are coupled to the same first-level power cell. Further, more of the secondary windings of the third transformer are to couple to the same first level power cell than second transformer phase shifted secondary windings coupled to the same second level power cell.

Brief description of the drawings

1 FIG. 10 is a block diagram of a power converter in accordance with one embodiment of the present invention. FIG.

2 FIG. 12 is a block diagram of a power converter in accordance with another embodiment of the present invention. FIG.

3 FIG. 10 is a block diagram of a power converter in accordance with yet another embodiment of the present invention. FIG.

4 FIG. 12 is a block diagram of yet another embodiment of a power converter. FIG.

5 FIG. 12 is a block diagram of an asymmetric power converter in accordance with one embodiment of the present invention. FIG.

5A FIG. 12 is a block diagram of an alternate implementation of an asymmetric power converter in accordance with one embodiment of the present invention. FIG.

6 FIG. 12 is a block diagram of an asymmetric power converter in accordance with another embodiment of the present invention. FIG.

6A Figure 4 is a block diagram of an alternate implementation of an asymmetric power converter in accordance with another embodiment of the present invention.

7 FIG. 12 is a graphical representation of simulated primary and secondary output currents for the modular transformer of FIG 1 ,

8th FIG. 12 is a graphical representation of a simulated input current from a supply terminal of the modular transformer. FIG.

9 FIG. 10 is a block diagram of an inverter in accordance with still another embodiment of the present invention.

Detailed description

Embodiments may provide modular transformers having multiple phase shifted windings to achieve the highest power quality at a supply terminal while providing scalability and modularity for various inverter topologies, such as a series H-bridge inverter. In particular, in various implementations, both a primary winding and secondary windings of each modular transformer may be out of phase. Particular implementations of such a phase shift are discussed below. Thus, each modular transformer has a primary winding which is at least phase shifted with respect to its neighboring transformers.

By providing modular transformer technology with adequate phase shifting in both secondary windings and primary windings, the most problematic harmonics on the supply side of the multistage inverter can be eliminated. Furthermore, by providing modular transformer configurations, the need for a single large transformer, which may be difficult to manufacture, install, and package, can be eliminated.

wobei N_T die Anzahl der Transformatormodule ist; N_dc die Anzahl der isolierten Gleichstromquellen ist; N_S eine Integer-Anzahl der Anzahl von Sekundärwicklungen in jedem Transformator ist; N_ph die Anzahl von Phasen einer Versorgung ist; α_sec die Sekundärwicklungenphasenverschiebung in jedem Modul ist; und α_prim die Primärwicklungsphasenverschiebung in jedem Modul ist.In various implementations, each transformer has at least one set of primary windings and a set of secondary windings, each set relating to polyphase windings (eg, three phase windings). As used herein, a winding may designate a set of windings (eg, a set of secondary windings coupled to a three-phase power cell). Both primary and secondary windings may be out of phase for optimal cancellation of harmonics. The degree of phase shift of secondary and primary windings can be calculated according to the following equations:

where N _{T is} the number of transformer modules; N _{dc is} the number of isolated DC sources; N _{S is} an integer number of the number of secondary windings in each transformer; N _{ph is} the number of phases of a supply; α _{sec is} the secondary winding phase shift in each module; and α _{prim is} the primary winding phase shift in each module.

For example, if the number of DC isolated power _sources needed is N _dc = 9, with N _T = 3 transformer modules (and assuming a three-phase supply), the phase shift between secondary windings of each transformer can be calculated as: N _S = 9/3 = 3; and α _sec = 360/18 = 20 °. The primary winding phase shift (between each transformer) can in turn be calculated as: α _prim = 20/3 = 6.7 °.

Now referring to 1 Referring now to the drawings, there is shown a block diagram of a power converter in accordance with one embodiment of the present invention. As in 1 shown includes system 100 several modular transformers 110a - 110c (generally transformer 110 ). As shown, every transformer is 110 coupled to a supply terminal U, which provides three-phase power to the transformers. Every transformer 110 again comprises a primary winding 112p and several secondary windings 112s (Note that for ease of illustration, such reference numbers apply only to the first transformer 110a are displayed).

For each primary transformer 110 is its primary coil 112p out of phase with respect to its neighboring transformers. In the particular implementation shown is at the first transformer 110a the primary winding 112p at a phase shift of -6.7 °, at the second transformer 110p is the primary winding at 112p at 0 ° and the third transformer 110c is the primary winding 112p at a phase shift of + 6.7 °. The phase shifts for this configuration can be obtained using equations 1-3 above. Therefore, given a given number of DC sources (ie, power cells) and a given number of transformers N _T and supply phases, the phase shift of the primary and secondary coils can be determined.

As further in 1 shown, each transformer includes 110 several secondary windings 112s which are also out of phase. In the implementation, which in 1 is shown, each of the secondary windings is phase shifted by 20 °.

The output of each of the secondary windings 112s thus provide three-phase AC power for a corresponding power cell 120a1 - 120c3 ready. Note that power cells 120a1 - 120a3 are coupled in series as a phase output line P1, which is a motor 130 Provides a first phase performance. Likewise, power cells provide 120b1 - 120b3 its phase output line P2, with motor 130 coupled, performance of a second phase ready. performance cells 120c1 - 120c3 put their phase output cable P3 with motor 130 coupled, in turn, power of a third phase ready.

The modular transformers can be manufactured using transformer manufacturing techniques and implement various types of winding designs for both primary and secondary windings. In the in 1 As shown, the primary windings include both extended delta configurations and a standard delta configuration. However, the use of primary and secondary windings can be freely selected. In various implementations, a desired phase shift may be realized by changing the geometry of the winding, for example by adjusting the number of turns of one or more coils of the transformer or the taps with respect to other coils. By controlling the number of turns of coils and a connection method therefor, a given phase shift can be realized. As in the implementation of 1 Secondary windings may include standard delta configurations as well as polygon configurations, again, by varying the size and / or turns of one or more coils, different phase shifts may be obtained. Of course, other configurations or connections may be used to realize a desired phase shift in various implementations. By phase shifting in the primary windings as well as in the secondary windings of transformer modules, the manufacturing process can be simplified by implementing small phase angles (eg 4 ° for a 90-pulse transformer, 15 power cells to supply) in secondary windings is not needed. The main obstacle to implementing a phase shift in secondary windings is the smaller number of turns in secondary windings (LV side) relative to primary windings (HV side). The smaller number of turns in secondary windings gives less freedom to realize smaller phase shift angles.

In various implementations, each modular transformer provides isolated three-phase power to one or more power cells of the same voltage from each phase output line. By separating a transformer into modular units, there is more surface area for the core and it can dissipate heat more effectively. Furthermore, each modular core volume may be reduced in size since the winding window must accommodate only one or a small number of secondary windings per output phase. In addition, the use of modular transformers will benefit the placement of the inverter. However, the cross-sectional area of the core may be substantially the same as in a single transformer implementation to ensure equal flux density. Also, the secondary copper windings may have the same wire thickness because the current density remains constant. Thus, while the average flux path for a modular core may be shorter, the combined volume between all modular cores will be greater than the volume of a single transformer.

The modular approach allows a single transformer unit to be used over a wide voltage and power range. By increasing a number of modular units, a converter in accordance with one embodiment of the present invention is capable of higher voltage and lower harmonic distortion performance. Modular units can be easily removed to reduce costs and efficiently accommodate lower voltages. In contrast, a conventional transformer would have to be completely redesigned for other rates. By providing a modular transformer instead, more suppliers may be able to make such a smaller transformer.

Modular transformers in accordance with one embodiment of the present invention can provide a variety of advantages, including better cancellation of harmonics and reliability. With respect to the benefits of harmonic cancellation, these modular transformers can provide better power quality in the supply because the phase shift of the primary and secondary can provide an N-pulse output that has a harmonic distortion in the supply current that is less than the requirements of Standards IEEE 519 , Such harmonic levels far exceed those possible with a single transformer because the mechanical tolerances at the careful phase angles required for such a system cause higher harmonic distortion. Furthermore, the modular transformers as a whole may have a common voltage and current level so as to cancel harmonics due to matching the outputs.

Furthermore, modular transformers can provide advances in reliability as various concerns inherent in a single transformer can be avoided by providing many smaller modular transformers. For example, concerns about short circuits from winding to winding can be reduced by isolating the multiple secondary sides in different modular transformers. Furthermore, thermal effects can be removed, such as a skin effect caused by configuring other windings over inner windings. Furthermore, by providing smaller separate modular transformers, avalanche of errors can be avoided. Further, by having multiple transformers in place, in the event of a fault from a transformer, the remaining transformers may permit further system operation despite a potentially lower power level. Embodiments may further include various bypass or switching mechanisms so as to enable dynamic removal of one or more transformers in the event of a fault. In addition, modular transformers reduce leakage in comparison to a single transformer with many secondary sides. Smaller leakage causes better use of iron and lower core losses.

As in 1 shown, every transformer has 110 a three-phase input with isolated three phase secondary output. primaries 112p Each transformer may have taps that phase-rotate relative to other modular transformers 110 enable. Such a phase rotation can match equation 3 from above. The turns ratio between the primary side and the secondary side can be individually selected for the desired output voltage level. In asymmetric configuration implementations, the turns ratio for one or more of the transformers may differ to accommodate different output voltages.

1 also shows a method for implementing one of the power cells 120 , Note that each of these power cells can be formed with the same topology. In particular, a power cell 120 be coupled to receive incoming power from a given modular transformer connected via a rectifier 130 rectified, which can be formed from a parallel implementation of diodes. With rectifier 130 is a power storage unit 140 coupled, which may include one or more storage capacitors. A switching stage 150 again, which may also be a so-called H-bridge implementation, may include a plurality of switching elements Q1-Q4, which may take the form of a power transistor, such as insulated gate bipolar transistors (IGBTs). Switching transistors can be protected by parallel-coupled counter diodes D1-D4. Switching of switching elements Q1-Q4 may be according to a local cell control 160 be implemented, which in turn control signals via a phase-optical interface 170 from a system control. While using this particular implementation in the embodiment of 1 is shown, the scope of the present invention is not limited in this respect.

In the example of 1 Each module transformer is an 18-pulse transformer. However, by applying the phase shift in the primary winding of the modular transformer, it acts as a 54-pulse transformer. Thus, while only three modular transformers are provided, each having a single primary winding and three secondary windings, harmonic cancellation of a 54-pulse transformer is realized. While in 1 with secondary windings configured as delta or extended polygonal connections and primary windings configured as delta or extended delta links, the scope of the present invention is not limited thereto. In other implementations, the secondary and primary windings may be connected in an extended star, zigzag, extended delta and polygon configurations as well.

Further, it is understood that in some implementations, an inverter formed from multiple modular transformers and corresponding power cells may include at least one transformer that is not out of phase. However, the power cells that receive power from such a non-phase-shifted transformer may be controlled using electronic means, thus allowing relatively harmonic distortion-free sine wave output. Thus, some embodiments may enable a combination of active and passive rectifiers. Namely, the phase-shifted transformers can provide passive phase rectifiers, such as diode rectifiers, while active phase shifts, such as in the form of input switching mechanisms of power cells coupled to a non-phase-shifted transformer, allow for equivalent control of an inverter. In such cases, therefore, an equivalent N-pulse inverter can be realized using a combination of phase shifted and non-phase shifted transformers.

Furthermore, it is understood that while in a three-phase system in the embodiment of 1 modular transformers can be used in various multiphase systems, such as systems with more than three phases (both in the input and output sides), such as a five-phase, six-phase, nine-phase system, etc. In such systems, similar Configurations of transformers and power cells are implemented.

Referring now to 2 Fig. 12 is a block diagram of a power converter in accordance with another embodiment of the present invention. As in 2 shown includes system 200 four modular transformers 210a - 210b , each of which is a primary page 212p and 3 secondary windings 212s having. In the implementation of 2 For example, the primary windings may be out of phase with each other by 5 degrees, and each may be configured as an extended Y configuration. Note that the phase shifts for the primary windings in 2 are shown to be a substantial mid-point between the modular transformers (ie, between the middle two modular transformers) at a 0 ° phase shift, so that the middle two transformers have primary windings of + 2.5 ° phase shift respectively. 2.5 °.

The secondary windings 212s Each transformer may in turn have a phase shift of 20 ° and may be configured as a Y configuration or an extended Y configuration. Thus, in the system 200 modular transformers 210a - 210d 12 isolated DC power sources, namely power cells 220a1 - 220c4 , In the embodiment of 2 Each power cell can be designed exactly like the power cells in 1 , Thus, in the implementation of 2 the system acts as a 72-pulse transformer. Note that the selected phase angles in the implementation of 2 in accordance with equations 1 to 3 can be determined so that N _{s is} 3, α _{sec is} 20 ° and α _{prime is} 5 °.

Now referring to 3 Referring now to the drawings, there is shown a block diagram of a power converter in accordance with yet another embodiment of the present invention. As in 3 shown includes system 300 three modular transformers 310a - 310c , Each transformer comprises a single primary coil 312p and four secondary windings 312S , In the implementation shown, the primary pages may be Y or extended Y configurations and the secondary pages may be extended Y configurations or other configurations. As in the implementation of 3 For example, at least two secondary windings of each transformer may be coupled to multiple power cells of a single phase output line. For example, two secondary windings of transformer 310a with power cells 320a1 and 320a2 be coupled. The remaining two secondary coils of transformer 310a may each be coupled to a power cell of the other two phase lines (namely, power cells 320b1 and 320C2 ). While shown with this particular implementation, the coils can be connected in some way to the different power cells. Thus, connections between the secondary windings and the power cells can be reversed as desired. This is because in various implementations the power cells can be of the same configuration and thus can receive power from any given secondary winding. That is, any of the power cells 320 can be through one or more secondary windings of any transformer 310 so that full interchangeability can be realized since any secondary output (in any phase) can be provided by any of the modular transformers of any given power cell. Interchangeability of power supplies to power cells can be realized by balancing power that must be supplied to the power cells. In the implementation of 3 Again, a 72-pulse transformer is realized by the three modular transformers driving the 12 individual power cells. As described above, every power cell can 320 be designed the same as with respect to 1 described.

Now referring to 4 Referring now to the drawings, there is shown a block diagram of still another embodiment of a power converter. In this implementation, five modular transformers 410a - 410e be present, with the primary winding 412p each of them has a phase shift of 4 °. Each modular transformer can in turn have three secondary windings 412s having 20 ° phase shifts. In essence, system can 400 similar to that of 1 be arranged with the addition of two additional modular transformers, so that 15 isolated DC sources corresponding to the power cells 420a1 - 420c5 can be driven.

Embodiments may also be applied to asymmetric cascaded multilevel inverters. 5 is a block diagram of an asymmetrical cascaded inverter 500 , the three power cells 520A1 - 520c3 per phase. In 5 For example, the input power supply to the inverter is implemented by three modular transformers, each transformer 510a - 510c seven secondary windings 512P having. The total required number of isolated DC sources N _dc is 21, thus N _{s is} 7. Thus, α _sec = 360/42 = 8.57 ° and α _prim = 8.57 / 3 = 2.86 ° in accordance with Equations 1 -3.

As in 5 shown, the phase-shifted primary windings 512P , which may be implemented as Y or extended Y configuration, each with seven secondary windings 512s coupled, which can be formed as Y or extended Y configurations. As shown, a plurality of secondary windings of each transformer may be coupled to a first power cell of each phase output line including a high voltage cell 520A1 (and 520B1 and 520c1 ) can be. A smaller number of secondary windings of each transformer may be coupled to a second power cell of each phase output line having a corresponding medium voltage cell 520a2 (and 520b2 and 520c2 ) can be. Finally, a single secondary winding of each transformer can be coupled to a corresponding low voltage power cell of each phase output line (namely, power cells 520a3 to 520c3 ). This type of configuration produces more voltage levels or less voltage harmonics for the motor. While using this particular implementation in the embodiment of 5 It is understood that various amounts of secondary windings of the transformer can be coupled to different power cells.

5 Further, there is shown a block diagram for each different asymmetric type of power cell present in the embodiment. As shown, the high voltage cells (e.g. 520A1 ) a rectifier stack 540 , a storage level 550 and a switching stage 560 , Note that four rectifier diodes coupled in series in this high voltage cell of the embodiment of FIG 5 are available to provide the high voltage output. In Different implementations can be any rectifier diode, which in the schematic view of 5 is shown to be implemented as a single rectifier diode, which may be a half-wave, full-wave rectifier or any topology. Note that in the embodiment of 5 each rectifier diode from high voltage cell 520A1 is coupled to receive incoming power from a set of secondary windings. That is, each rectifier diode is associated with a single secondary winding. By using several such rectifier diodes, a better power balance can be achieved. In a particular embodiment of a 6600 V center drive, the high voltage cells may output a voltage of between 0 and 2178 volts. Further, while shown for ease of illustration as a single H-bridge, in some embodiments the high voltage cells may be formed using a multi-level H-bridge configuration, such as a three-level H-bridge configuration. The medium voltage cells in turn (eg represented by 520 ) comprise a similar but smaller rectifier diode stack 540 (where each rectifier diode is still coupled to a single set of secondary windings), memory level 550 and switching stage 560 , In the same particular embodiment of a 6600V medium voltage drive, the medium voltage cells may output a voltage between 0 and 1089 volts. The low voltage cells, as well as by power cell 520a3 represent similar components. As in 5 2, its rectifier stage may be implemented using only a single rectifier diode coupled to a set of secondary windings in some embodiments. In a particular embodiment, the low voltage cells may output a voltage of between 0 and 544 volts. Thus, the total voltage with which the motor is according to 5 is supplied 3810 volts per phase or 6600 volts of voltage from line to line. Thus, in the implementation of 5 relatively smaller modular transformers are provided at equal voltages, wherein the number of rectifiers of each voltage level power cell corresponds to the number of sets of secondary windings coupled to the voltage level cell. By using an asymmetric configuration such as that of 5 , can the engine 530 be provided a higher output. Also, the input current to the driver includes fewer harmonic components by using multiple power cell power supplies and phase shifting in primary and secondary sides. This power quality of the drive is achieved by erasing harmonic components by implementing phase shift in primary windings and secondary windings of the transformer modules. While the specific configuration that in 5 1, assigns power cells to a single phase output line to each modular transformer, the scope of the invention is not limited in this respect. Furthermore, while a three-level inverter is shown, more or less asymmetric levels may be present in a given implementation.

5A shows an alternative implementation of an asymmetrical inverter 500 ' using three modular transformers. In this implementation, the secondary sets of windings of each transformer were interchangeably coupled to different power cells of three different levels. For example, the power cell is first level 520A1 with secondary sets of windings of both the first transformer 510a as well as the second transformer 510b coupled. Likewise, the power cell is second level 520a2 with secondary sets of turns of the second transformer 510b and the third transformer 510c coupled. Power cell third level 520a3 is with a secondary set of windings from the third transformer 510c coupled. The other phase lines include similarly coupled power cells. While shown with this particular implementation, other implementations may provide other exchangeable connections between secondary sets of windings and any of the transformers with any power cell. Furthermore, it is understood that while in a three-phase system in the embodiment of 5 Asymmetric modular transformers can be used in various multiphase systems, such as systems with more than three phases (both on the output and input sides), such as a five-phase, six-phase, nine-phase system, etc. In such systems, similar configurations of Transformers and power cells are implemented.

Now referring to 6 Fig. 3 shows a block diagram of an asymmetrical power converter in accordance with another embodiment of the present invention. As in 6 shown includes system 600 seven modular transformers 610a - 610g , The total required number of isolated DC sources (N _dc ) is 21, so N _{s is} three. Thus, α _sec = 360/18 = 20 ° and α _prim = 20/7 = 2.86 ° in accordance with equations 1 to 3.

As shown in this implementation, secondary windings can 612s of several modular transformers to be coupled to the same phase output line.

In particular as in 6 shown includes system 600 Power cells of different voltage levels, comprising a first set of high voltage power cells 620a1 - 620c1 , a second set of medium voltage power cells 620a2 - 620c2 and a third set of low voltage power cells 620a3 - 620c3 which are coupled to a motor 630 Provide power. As can be seen, different numbers of secondary coils from different transformers are coupled to each of these power cells. In the particular implementation of 6 have modular transformers 610a - 610d Secondary windings connected to the high voltage power cells 620a1 - 620c1 are coupled while modular transformers 610e and 610f Have secondary windings with medium voltage power cells 610a2 - 620c2 are coupled. Finally, the modular transformer 610g its secondary windings with the low voltage power cells 620a3 - 620c3 coupled. The primary windings 612P The modular transformers may be configured as delta or extended delta configurations while the secondary winding 612s may be formed as delta or extended polygon configurations, although the scope of the present invention is not limited in this respect. As in 6 As can be seen, the asymmetric power cell configurations may be the same as those above 5 described.

6A shows an alternate implementation 600 ' of the embodiment of 6 , where seven transformers are coupled to the three power level cells of the three-phase lines. As in the implementation of 6A shown are the first to fourth transformers 610a - 610d each with first level power cells 620a1 - 620a3 coupled. Fifth and sixth transformer 610e - 610f are again with second-level power cells 620a2 - 620a3 coupled. Finally, a seventh transformer 510g a secondary set of windings associated with each of the third level power cells 620a3 - 620c3 is coupled. Again, these are interchangeable configurations that are in 6A and other implementations may be configured differently.

7 shows simulated primary-side and secondary-side output currents for transformers 110a from 1 , Values start from a 4160 volt inverter for a motor of 1000 horsepower. 8th again shows a simulated input current from a supply terminal to the modular transformers. By providing phase shift in the primary windings as well as the secondary windings, more harmonics can be erased so that the overall harmonic distortion (THD) can be lowered. By using modular transformer technology, as in 1 For example, the total harmonic distortion of an input current to the transformer is approximately 4.5%, which is in line with the requirements of Standard IEEE 519 perfectly compatible. However, without implementation of phase shift in primary sides, the total harmonic distortion of input current will be about 7.1%. These numbers show a significant improvement over a single transformer with no phase shift in primary sides. Note the differences in currents between the input streams for the system that is in 8th is shown and the input current to the primary winding of each modular transformer as in 7 shown. Connecting multiple modular transformers also improves the power factor while eliminating more harmonic currents. The primary side of each modular transformer will contribute approximately one-third of the total input current to the driver. Thus, in various embodiments, optimal harmonic cancellation on the input side to the transformers may be realized by providing phase shifted windings on both the primary and secondary side of the modular transformers, the phase shift being in accordance with equations 1-3. Accordingly, not only are harmonics reduced, but they are reduced to an optimal level, as low as possible at a reasonable cost of the transformer implementation.

As mentioned above, in other implementations, a combination of active and passive phase shifting may be present in an inverter. Now referring to 9 Fig. 3 shows a block diagram of an inverter in accordance with yet another embodiment of the present invention. In particular shows 9 an implementation of a symmetrical cascaded medium voltage inverter with partial regeneration capability for a three phase motor. As in 9 shown, the inverter can 900 modular transformers 910b and 910c with passive phase shifting, which is realized by both phase shifts of primary windings and secondary windings. Furthermore, at least one further modular transformer 910a be provided, which is not out of phase. However, the outputs of this modular transformer can be provided to power cells of a different configuration than those of the other power cells. In particular, these power cells can 920a1 - 920c1 be regenerative power cells having an active input, z. By IGBTs 905 implemented. If these input IGBTs are controlled accordingly, For example, a relatively pure sinusoidal current is realized in the main side (ie power cell input current) with minimal harmonic distortion.

Nonetheless, the winding sets of the primary and secondary transformer modules 910b and 910c which power the other power cells to be phase shifted to minimize the harmonics in the main current. In this example, N _dc = 6 and T _T = 2 such that N _S = 3. Since N _ph = 3, α _{prim is} 20 ° and α _sec = 10. Thus, in the embodiment of FIG 9 an equivalent 36-pulse transformer using two 18-pulse transformers 910b and 910c be realized with phase-shifted primary pages. However, the phase shift for the transformer module 910a not needed, as the electronically controlled active input 905 the power cell will receive almost pure sinusoidal power from the supply.

Further, by providing an active input, this implementation provides the opportunity for partial regeneration. Of course, other implementations using different combinations of active and passive transformers are possible, as well as a control means for actively controlling one or more power cells. Note in the embodiment of 9 can be a control 980 which may be a local or master control to which power cells are coupled (note that the connections in 9 not shown for ease of illustration). Furthermore, this control may include control of the active circuitry of the input IGBTs of the power cells 920a3 - 920c3 to enable a clean sine wave output, as well as to allow a partial regeneration mode.

While the present invention has been described with reference to a limited number of embodiments, those skilled in the art will recognize numerous modifications and variations thereof. It is intended by the appended claims to cover all such modifications and variations that fall within the true spirit and scope of the present invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Standards IEEE 519 [0035]
• Standard IEEE 519 [0054]

Claims (17)

Apparatus comprising: a plurality of transformers, each providing an output for at least one of a plurality of power cells configured to provide AC power to a load, each of the plurality of transformers comprising: at least one primary winding and a plurality of secondary windings, wherein the at least one primary winding of each of the transformers is phase shifted with respect to its adjacent transformers, and the plurality of secondary windings are phase shifted with respect to the other secondary windings of the respective transformer, wherein the phase shift of the at least one primary winding is due to the phase shift of the secondary windings based on a number of multiple transformers. The apparatus of claim 1, wherein the phase shift of the at least one primary winding is α _sec / N _t , where N _{t is} the number of multiple transformers and α _sec corresponds to the phase shift between two of the secondary windings of a respective transformer, and 360/2 N _ph N _s , where N _{ph is} a number of phases of a supply of the plurality of transformers and N _{s is} an integer number of the secondary windings in each of the transformers. The device of claim 2, wherein the number of secondary windings per transformer corresponds to N _dc / N _t , where N _{dc is} a number of the plurality of power cells coupled to the plurality of transformers. The apparatus of claim 1, further comprising a non-phase shifted transformer to provide an output for at least one second power cell. The device of claim 1, wherein a plurality of secondary windings of a first transformer are coupled to a first power cell and at least one secondary winding of the first transformer is coupled to a second power cell, and the first power cell and the second power cell are asymmetric, and wherein at least one further secondary winding of the first first transformer is coupled to a third power cell. System comprising: a plurality of modular transformers, each including at least one out-of-phase primary set of windings for receiving power from a supply terminal and comprising a plurality of secondary sets of windings; and a plurality of power cells, each coupled to one of the secondary sets of windings of one of the modular transformers, wherein a first subset of the power cells is coupled to a first phase output line, a second subset of the power cells is coupled to a second phase output line, and a third subset of the power cells is coupled to a third phase output line, and wherein each modular transformer provides an output of a first number of power cells of a pair of the three phase output lines and a second number of power cells of a last of the phase output lines, wherein the first number of power cells and the second number of power cells from each other and wherein any one of the plurality of power cells may be coupled to any of the secondary sets of windings of any one of the plurality of modular transformers. The system of claim 6, wherein each modular transformer provides the output of the first number of power cells of another pair of the three phase output lines. The system of claim 6, wherein a phase shift of the phase-shifted primary sets of windings α _sec / N _t , where N _{t is} the number of multiple modular transformers, and α _sec corresponds to a phase shift of the secondary sets of windings of a corresponding modular transformer, and on a Number of phases of the supply terminal coupled to the modular transformers and the number of secondary sets of windings per modular transformer based in turn on a total number of the power cells and N _t . The system of claim 8, wherein α _sec corresponds to 360/2 N _ph N _s , where N _{ph is} a number of phases of the supply connection to the plurality of modular transformers and N _{s is} an integer number of secondary sets of windings in each of the modular transformers , A system comprising: a plurality of modular transformers each including a phase shifted primary winding coupled to an input power source and a plurality of phase shifted secondary windings, each coupled to a power cell; a first phase output line having at least a first level power cell and a second level power cell, a first one of the modular transformers having a first plurality of the phase shifted secondary windings connected to the first level power cell and having a second plurality of the phase-shifted secondary windings coupled to the second-level power cell; a second phase output line having at least a first level power cell and a second level power cell, a second one of the modular transformers having a first plurality of the phase shifted secondary windings coupled to the first level power cell and a second plurality of the phase shifted secondary windings are coupled to the second level power cell; and a third phase output line having at least a first level power cell and a second level power cell, a third of the modular transformers having a first plurality of phase shifted secondary windings coupled to the first level power cell and a second plurality of phase shifted secondary windings. which are coupled to the power cell second level. The system of claim 10, wherein the first phase output line comprises a third level power cell, and wherein at least one of the phase shifted secondary windings of the first modular transformer is coupled to the third level power cell, wherein the power cell is a first voltage higher level than the second level power cell , and the second level power cell is for a higher voltage than the third level power cell, and wherein each of the plurality of modular transformers are of the same output level. The system of claim 10, wherein the first level power cell comprises a rectifier stack having a larger number of diodes than a second level power cell rectifier stack, and wherein each of the first power cell diodes is coupled to one of the first plurality of phase shifted secondary windings. The system of claim 10, wherein the phase shift of the phase-shifted primary winding is α _sec / N _t , where N _{t is} the number of multiple modular transformers, and α _sec corresponds to the phase shift between two of the phase-shifted secondary windings of a corresponding modular transformer, and 360/2 N _ph N _s corresponds, where N _ph is a number of phases of the input power source, and N _s is an integer number of phase-shifted secondary windings in each of the modular transformers. Apparatus comprising: a plurality of modular transformers, each comprising at least one out-of-phase primary set of windings for receiving power from a utility terminal, and a plurality of secondary sets of windings; a plurality of first level power cells, each coupled to a first plurality of secondary sets of windings of at least two of the modular transformers, wherein a first of the first level power cells is coupled to a first phase output line, and a second of the first level power cells is coupled to a second phase output line and a third of the first level power cells is coupled to a third phase output line; and a plurality of second level power cells, each coupled to a second plurality of secondary sets of windings of at least two of the modular transformers, wherein a first of the second level power cells is coupled to the first phase output line, and a second of the second level power cells is coupled to the second phase output line and a third of the second level power cells is coupled to the third phase output line, wherein each of the first level power cells and the second level power cells may be coupled to any one of the secondary sets of windings of any one of the plurality of modular transformers. The apparatus of claim 14, further comprising a plurality of third level power cells, each coupled to at least one of the secondary sets of windings of at least one of the modular transformers, wherein a first of the third level power cells is coupled to the first phase output line, a second one of the power cells third level is coupled to the second phase output line and a third of the third level power cells is coupled to the third phase output line, wherein any of the third level power cells may be coupled to any one of the secondary sets of windings of any one of the plurality of modular transformers. The apparatus of claim 14, wherein the first level power cells include a first plurality of rectifiers, each coupled to one of the secondary sets of windings, and the second level power cells comprising a second plurality of rectifiers, each with one of the sets of Secondary windings is coupled, wherein the second plurality of rectifiers is less than the first plurality of rectifiers. The apparatus of claim 14, wherein a first set of the modular transformers has at least one of its secondary sets of windings coupled to each of the first level power cells and a second set of the modular transformers has at least one of its secondary sets of windings associated with each of Power cells second level is coupled.

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