WO2015090627A1

WO2015090627A1 - Power unit and multi-phase electric drive using the same

Info

Publication number: WO2015090627A1
Application number: PCT/EP2014/059484
Authority: WO
Inventors: Andreas Voegeli; Jukka Palomaki
Original assignee: Abb Technology Ltd.
Priority date: 2013-12-19
Filing date: 2014-05-08
Publication date: 2015-06-25
Also published as: CN104734529A

Abstract

It provides a power unit including: a multi-phase bridge rectifier, having inputs being electrically connectable to a source of multi-phase AC power; a smoothing filter, being connected to an output of said multi-phase bridge rectifier; and a multiple of H-bridge inverters; wherein: input terminals of said multiple of H-bridge inverters are electrically connected in parallel with said smoothing filter; and output terminals of said multiple of H-bridge inverters are electrically connected in parallel and are adapted for providing a single-phase output to an AC load. By having the power unit, it has one three-phase bridge rectifier thus it is helpful for eliminating the current sharing issues occurring among more than one three-phase bridge rectifiers. In addition, by having three H-bridge inverters electrically connected in parallel in the power unit, the current rate for the power unit is increased as compared with that with one H-bridge inverter. Preferably, a multiple of pre- charging resistors can respectively arranged between said output of said respective one of said multiple of legs of said multi-phase bridge rectifier and said respective one of said multiple of capacitor banks.

Description

Power Unit and Multi-phase Electric Drive Using the Same

Technical Field

The invention relates to the field of a power unit, and more particularly to a power unit used in a cascaded multi-phase electric drive.

Background Art

Cascaded multi-phase electric drives are used in industry to provide variable electric power to AC motors. These same drives can be used in other applications not related to specifically to motors but where a variable-output voltage or frequency is desired. Typical drives have an AC input power source and some type of conversion apparatus, usually using solid-state devices, for converting the fixed AC input voltage into a variable-voltage and/or variable-frequency output. One such type of drive is described in U.S. Pat. No. 5,625,545, which is incorporated herein by reference. That patent describes a power supply used as a drive which utilizes a number of power cells (power units) arranged to produce a three-phase AC output. Such multiple power units in series can be utilized to provide higher voltage outputs than would be available with only a single power unit.

IGBT modules are conventionally used for the power switches in the power cell. For example, dual IGBT modules in 62mm housings are very cost competitive but are only available up to 400 A ratings. This further limits the current ratings of the power cell of the cascaded multi-phase electric drive.

Brief Summary of the Invention

It is therefore an objective of the invention to provide a power unit and a multi-phase electric drive that overcomes at least part of the disadvantages in the prior art.

A power unit according to the present disclosure includes: a multi-phase bridge rectifier, having inputs being electrically connectable to a source of multi-phase AC power; a smoothing filter, being connected to an output of said multi-phase bridge rectifier; and a multiple of H-bridge inverters; wherein: input terminals of said multiple of H-bridge inverters are electrically connected in parallel with said smoothing filter; and output terminals of said multiple of H-bridge inverters are electrically connected in parallel and are adapted for providing a single -phase output to an AC load. By having the power unit, it has one three-phase bridge rectifier thus it is helpful for eliminating the current sharing issues occurring among more than one three-phase bridge rectifiers. In addition, by having three H-bridge inverters electrically connected in parallel in the power unit, the current rate for the power unit is increased as compared with that with one H-bridge inverter.

Preferably, a multiple of pre-charging resistors can respectively arranged between said output of said respective one of said multiple of legs of said multi-phase bridge rectifier and said respective one of said multiple of capacitor banks.

Further embodiments, aspect, and details are evident from the detailed description, the figures, and the dependent claims. Brief Description of the Drawings

The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:

Figure 1 shows a power circuit diagram for a cascaded multi-phase drive having three power units in each phase;

Figure 2 shows a typical power unit as shown in figure 1 ;

Figure 3A shows a power unit according to an embodiment of present invention;

Figure 3B shows a power unit according to anther embodiment of present invention as an alternative to that of figure 3A;

Figure 3C shows a power unit according to another embodiment of present invention; Figure 4A shows the power unit according to figure 3 A with gate drives; and

Figure 4B shows the drive circuit for the power unit according to figure 4A.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

Preferred Embodiments of the Invention

Figure 1 shows a power circuit diagram for a cascaded multi-phase drive having three power units in each phase. As shown in figure 1, three-phase AC power is inputted to primary winding 100 of power supply transformer 10 of a cascaded multi-phase drive 1. Primary winding 100, which may be star- or mesh-connected, energizes three-phase secondary windings 101 through 109. The three-phase power associated with each of secondary windings 101 through 109 can be supplied to power units 110 through 118, respectively. In this present embodiment it is preferred to provide mesh-connected secondary windings 101 through 109 to lower the supply transformer's K-factor and to improve harmonics control. Mesh-connected winding may include, for example, delta or extended delta configurations. Under certain circumstances, such mesh windings may be manipulated to advance some of the secondary windings by preselected degrees of electrical phase, to retard other secondary windings by preselected degrees of electrical phase, and, perhaps, to leave other secondary windings substantially un-shifted in phase. In the present embodiment shown in figure 1, it is described that one-third of the secondary windings be advanced in phase by 20 (degree) and that one-third of the secondary windings be delayed in phase by 20 (degree). The remaining third of the secondary windings remain un-shifted. In the embodiment of figure 1, the phase-shifted windings use extended-delta-configured windings, and the un-shifted windings use delta-configured windings. For other voltages, the respective phase shift needed can be obtained by dividing 60 (degree) by the number of power units per phase. For example, with 5 power units per phase, the shifts are +24 (degree), +12 (degree) , 0 (degree) , -12 (degree) and -24 (degree); with 6 power units per phase, the shifts are +25 (degree), +15 (degree) , +5 (degree) , -5 (degree), -15 (degree) and -25 (degree); with 8 power units per phase, the shifts are +18.75 (degree), +11.25 (degree), +3.75 (degree) , -3.75 (degree), -11.25 (degree) and -18.75 (degree). It is preferred to connect multiple power units to each of phase output lines 120, 121, 122, which can represent phase A, Phase B and Phase C, respectively. Multiple power units can be connected in series on each phase output line, making it possible to produce a medium- voltage input phase line controller with a plurality of low-voltage power units. Serial connections also make multiple voltage states per phase possible; these multiple voltage states per phase may be used to obtain improved current waveforms. Each power unit may be constructed internally to low- voltage standards, for example, each power unit may have a 1000-volts rating, despite its inclusion in a medium- voltage apparatus. In such an embodiment, the individual power units may be isolated from ground, and other power units, using insulation suitable for the medium voltage level being used.

Figure 2 shows a typical power unit as shown in figure 1. However, it is to be understood that other power units can be utilized in practicing this invention. The power unit shown in Figure 2 is similar to that shown in U.S. Pat. No. 5,625,545. As show in figure 2, each of power units 110 through 118 is a power converter which converts the three-phase incoming power into a DC component through utilization of a three-phase bridge rectifier composed of diodes 20a -20f. The output of this three-phase bridge rectifier is then directed across capacitor 21, which can provide storage and smoothing of the DC output. The DC power in the converter can be selectively applied to the power unit outputs 22a and 22b using a pulse-width modulated (PWM) method. The pulse-width modulation may be implemented using a bridge converter which is composed of semiconductor switches such as 23a-23d. Any type of acceptable switch element can be used; and depending on the power level, various solid-state components may be chosen. As shown, the converter output utilizes four IGBTs. In such a pulse- width modulated operation the switches can be considered either fully on or filly off as they operate. As will be understood in most applications, it is desirable that the power units utilized in a cascaded arrangement be similar and constructed in a form so as to limit the number of subassemblies and permit power units to be interchangeable within the same drive. Power unit 110 through 118 as shown in figure 2 could be utilized for all of the power units in figure 1.

Figure 3A shows a power unit according to an embodiment of present invention. As shown in figure 3A, the power unit 3 includes a three-phase bridge rectifier 30, a smoothing filer 31, three H-bridge inverters 32, 33, 34. The three-phase bridge rectifier 30 has inputs 30A, 30B, 30C electrically connectable to a source of three-phase AC power, which can convert the three-phase incoming power into a DC component. The output of the three-phase bridge rectifier 30 is then directed across the smoothing filer 31, which can provide storage and smoothing of the DC output. The smoothing filter 31 can be, for example a capacitor bank. The input terminals of the H-bridge inverters 32, 33, 34 are electrically connected in parallel with the smoothing filer 31. The output terminals of the H-bridge inverters 32, 33, 34 are electrically connected in parallel and are adapted for providing a single-phase output to an AC load. The DC power in the smoothing filter 31 can be selectively applied to the power unit outputs 35a and 35b using a pulse-width modulated (PWM) method. The pulse- width modulation may be implemented using the H-bridge inverters 32, 33, 34 electrically linked in parallel, each of which is composed of semiconductor switches such as 32a-32d, 33a-33d, and 34a-34d. Any type of acceptable switch element can be used; and depending on the power level, various solid-state components may be chosen. As shown, the converter output utilizes four IGBTs. In such a pulse- width modulated operation the switches can be considered either fully on or filly off as they operate. As will be

understood in most applications, it is desirable that the power units utilized in a cascaded arrangement be similar and constructed in a form so as to limit the number of

subassemblies and permit power units to be interchangeable within the same drive. Power unit 3 as shown in figure 3 A could be utilized for all of the power units in figure 1. If three power units according to figure 2 are electrically connected in parallel, there will be a current sharing issues among the three-phase bridge rectifiers of the three power units due to the various current- voltage characteristic of the power diodes utilized in the three three- phase bridge rectifiers of the power unit. By having the power unit according to figure 3A, it has one three-phase bridge rectifier thus it is helpful for eliminating the current sharing issues occurring among more than one three-phase bridge rectifiers. In addition, by having three H-bridge inverters electrically connected in parallel in the power unit, the current rate for the power unit is increased as compared with that with one H-bridge inverter.

Referring to figure 3A, it is to be understood that for a three-phase bridge rectifier 30, six diodes 30a-30f are used, and the circuit has a pulse number of six. The three-phase bridge rectifier 30 has three legs, each of which has two diodes (two sets of diodes) in series, such as diodes 30a, 30b in series, diodes 30c, 30d in series, and diodes 30e, 30f in series, with the anode of the first diode connected to the cathode of the second, and is manufactured as a single component for this purpose.

Figure 3B shows a power unit according to anther embodiment of present invention as an alternative to that of figure 3A. The power unit according to figure 3B is different from that according to figure 3A in that: each of the diodes of the three-phase bridge rectifier 30 is replaced with three diodes electrically connected in parallel allowing the current to pass in the same direction as the replaced one does. For example, diode 30a in figure 3A is replaced by diodes 30ax, 30ay, 30az, diode 30b in figure 3A is replaced by diodes 30bx, 30by, 30bz, diode 30c in figure 3A is replaced by diodes 30cx, 30cy, 30cz, diode 30d in figure 3A is replaced by diodes 30dx, 30dy, 30dz, diode 30e in figure 3A is replaced by diodes 30ex, 30ey, 30ez, diode 30f in figure 3A is replaced by diodes 30fx, 30fy, 30fz. By having such replacement, the current flows in the rectifier is conducted by three diodes electrically connected in parallel, thus the current rate for the rectifier is increased as compared.

By referring to figures 3 A and 3B, it is to be understood that the number of diodes in the diode set of each leg may be selected depending on the requirement of the current rate for the rectifier.

Figure 3C shows a power unit according to another embodiment of present invention. The power unit according to figure 3C is different from that according to figure 3A in that: it further includes inductance means 36a, 36b electrically connected between the outputs 35a, 35b and the AC load. The inductance means is helpful for compensation of switching timing differences between paralleled switch semiconductors, because inductance helps to reduce the current spick flowing from one IGBT to the other one if they do not switch exactly at the same time. It is to be understood that, from a mechanical configuration perspective, the H-bridge inverter can be implemented in IGBT modules, for example, in two one-phase IGBT modules electrically connected in parallel, and this package provides an easy way to cool the device and to connect it to the outer circuit. By referring to figures 3A, 3B, and 3C, the semiconductor switches 32a, 33a, 34a are electrically connected in parallel, the semiconductor switches 32b, 33b, 34b are electrically connected in parallel, the semiconductor switches 32c, 33c, 34c are electrically connected in parallel, the semiconductor switches 32d, 33d, 34d are electrically connected in parallel, so that the switching events of the parallel connected semiconductor switches can be controlled synchronously. Besides, the three-phase rectifier can be implemented in power diode modules, for example, in three one -phase rectifier modules electrically connected in parallel, and this package provides an easy way to cool the device and to connect it to the outer circuit.

It is to be understood that the power unit contains a first, a second, a third subassembly. The first subassembly includes a first one-phase rectifier 30a of the three-phase bridge rectifier 30, a first smoothing filer 31a of the smoothing filer 31, and the first H-bridge inverter 32; the second subassembly includes a second one-phase rectifier 30b of the three- phase bridge rectifier 30, a second smoothing filer 31b of the smoothing filer 31, and the second H-bridge inverter 33; and the third subassembly includes a third one -phase rectifier 30c of the three-phase bridge rectifier 30, a third smoothing filer 31c of the smoothing filer 31, and the third H-bridge inverter 34. As regards the inductance means 36a, 36b, they can be implemented in the mechanical configuration that, for example, the output terminals the power unit outputs 35a and 35b are mechanically arranged at an opposite side to the output terminals 32a, 32b of IGBT modules for the first H-bridge inverter 32 with respective to the location of the first smoothing filter 31a; the output terminals the power unit outputs 35a and 35b are mechanically arranged at an opposite side to the output terminals 33a, 33b of IGBT modules for the second H-bridge inverter 33 with respective to the location of the second smoothing filter 3 lb, and the output terminals the power unit outputs 35a and 35b are mechanically arranged at an opposite side to the output terminals 33a, 33b of IGBT modules for the first H-bridge inverter 33 with respective to the location of the third smoothing filter 31c. By having such configuration, the inductance can be provided by relatively long conductors connecting the IGBT modules and the output terminals of the power unit. Further, the degree of the inductance means 36a, 36b can be adjusted by a coiled conductor, and/or with a magnetic material being mechanically shaped and arranged to enclose a part of the coiled conductor. By having the coiled conductor, it is helpful for suppressing the short circuit current introduced by the switching time difference between the corresponding semiconductor switches 32a, 33a, 34a; 32b, 33b, 34b; 32c, 33c, 34c; and/or 32d, 33d, 34d,

Figure 4A shows the power unit according to figure 3 A with gate drives. It is to be understood that the gate drives are applicable to drive the power units according to figures 3B and 3C, and the gate drives are controlled by the power unit controller in a way that the DC power stored in the smoothing filter 31 is selectively applied to the power unit outputs 35a and 35b using a pulse- width modulated (PWM) method. As shown in Figure 4A, the power unit 3 further includes a gate driver 50 for controlling switching events of the semiconductor switches 32a, 33a, 34a electrically connected in parallel so that the switching events of them can be synchronized in time. It is to be understood that the power unit 3 can further include three gate drivers (not shown in Figure 4A) respectively controlling switching events of the semiconductor switches 32b, 33b, 34b as a group, the semiconductor switches 32c, 33c, 34c as a group, the semiconductor switches 32d, 33d, 34d as a group, and similarly the switching events of the switch semiconductors in each group can be synchronized in time. Such configuration is helpful achieving the

synchronization of the paralleled semiconductor switches.

Figure 4B shows the drive circuit for the power unit according to figure 4A. As shown in 4B, for each of the semiconductor switches in the same group, for example the group of the semiconductor switches 32a, 33a, 34a, the drive circuit includes three common mode chokes 50a, 50b, 50c. The first common mode choke 50a is electrically connected between the gate and emitter of semiconductor switch 32a and the gate driver 50, the second common mode choke 50b is electrically connected between the gate and emitter of semiconductor switch 33a and the gate driver 50, and the third common mode choke 50c is electrically connected between the gate and emitter of semiconductor switch 34a and the gate driver 50. The three semiconductor switches 32a, 33a, 34a are connected in parallel, and this might cause a transient gate voltage potential difference between the individual IGBT gates due to switching time deviations among the paralleled IGBT switches. This can result switching oscillations during the switching event or to excessive gate voltages that may damage the IGBT's. . By having the common mode chokes, it is helpful to overcome those issues because the common mode choke help to decouple the paralleled IGBT gates among each other during switching.

Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims

1. A power unit, including:

a multi-phase bridge rectifier, having inputs being electrically connectable to a source of multi-phase AC power;

a smoothing filter, being connected to an output of said multi-phase bridge rectifier; and

a multiple of H-bridge inverters;

wherein:

input terminals of said multiple of H-bridge inverters are electrically connected in parallel with said smoothing filter; and

output terminals of said multiple of H-bridge inverters are electrically connected in parallel and are adapted for providing a single-phase output to an AC load.

2. The power unit according to claim 1, wherein:

said multi-phase bridge rectifier includes a multiple of legs; and

each of the legs includes two sets of two-terminal power semiconductors electrically connected in series.

3. The power unit according to claim 2, wherein:

said two-terminal power semiconductor is a diode.

4. The power unit according to claim 1 or 2 or 3, further including:

a power unit controller, for controlling said single-phase output.

5. The power unit according to claim 4, wherein:

said power unit controller includes a multiple of gate drivers, being respectively adapted for controlling a switching event of each of said multiple of H-bridge inverters so that said switching event of respective one of said multiple of H-bridge inverters is synchronized in time with said switching event of respective others of said multiple of H- bridge inverters.

6. The power unit according to claim 5, wherein:

said H-bridge inverter includes a plurality of three-terminal power semiconductors in a H-bridge configuration; and

said respective one of said multiple of gate drives controls said switching events of a respective group of said three-terminal power semiconductors in parallel among said multiple of H-bridge inverters.

7. The power unit according to any of claims 1 to 6, wherein:

said smoothing filter includes a multiple of capacitor banks;

each of said multiple of H-bridge inverters are implemented in IGBT modules; and said respective one of said multiple of capacitor banks is connected in parallel with said respective one of IGBT modules of said multiple of H-bridge inverters.

8. The power unit according to any of claims 1 to 6, wherein:

said smoothing filter includes a multiple of capacitor banks;

each of said legs of said multi-phase bridge rectifier is of a one-phase rectifier module;

said respective one of said multiple of capacitor banks is connected in parallel with output of said respective one of said one-phase rectifier module of said multiple of legs of said multi-phase bridge rectifier.

9. The power unit according to claim 7 or 8, further including:

a multiple of pre-charging resistors, being respectively arranged between said output of said respective one of said multiple of legs of said multi-phase bridge rectifier and said respective one of said multiple of capacitor banks.

10. The power unit according to claim 6, or according to claim 7, 8 or 9 if directly or indirectly dependent on claim 6, further including:

a plurality of common mode inductors, being arranged between respective one of said multiple of gate drivers and said three-terminal power semiconductor for which it controls said switching event.

11. The power unit according to claim 7, wherein:

said output terminals of the power unit are mechanically arranged at an opposite side to output terminals of said IGBT module of said respective one of said multiple of H- bridge inverters with respective to said smoothing filter.

12. The power unit according to any of the preceding claims, further including:

a coiled conductor, for electrically connecting said output terminal of the power unit and said output terminal of said IGBT module of said respective one of said multiple of H- bridge inverters.

13. The power unit according to claim 12, further including:

a magnetic material, being mechanically shaped and arranged to enclose a part of said coiled conductor.

14. A multi-phase electric drive comprising the power unit according to any of claims 1 to 13, wherein the multi-phase electric drive includes:

a multi-phase power transformer, including at least one primary winding and a first number of secondary windings;

a first number of said power units, said inputs of said multi-phase bridge rectifier of each of said first number of power units are connected with a corresponding one of said first number of secondary windings, and said output terminals of a multiple of said first number of power units being serially connected with respective others of said power units in each phase output line for providing cascaded said single-phase outputs.