THREE-LEVEL T-TYPE NPC POWER CONVERTER

Abstract

A three-level converter includes a first converter leg having first switches connected across a positive DC node and a negative DC node, a second converter leg having second switches connected across the positive DC node and the negative DC node, and a third converter leg having third switches connected across the positive DC node the negative DC node. The converter includes a battery connected between the positive DC node and the negative DC node, and center-connected to a ground node having a ground potential. Each of the first, second, and third converter legs is connected to the ground node.

Claims

1. A three-level converter, comprising: a first converter leg having first switches connected across a positive DC node and a negative DC node; a second converter leg having second switches connected across the positive DC node and the negative DC node; a third converter leg having third switches connected across the positive DC node and the negative DC node; and a battery connected between the positive DC node and the negative DC node, and center-connected to a ground node having a ground potential, each of the first, second, and third converter legs connected to the ground node.

2. The three-level converter of claim 1, further comprising: first and second capacitors connected in series between the positive DC node and the negative DC node, a connection of a cathode of the first capacitor and the anode of the second capacitor connected to the ground node.

3. The three-level converter of claim 1, wherein the first, second, and third converter legs are arranged with one of a T-type neutral point clamped (T-NPC) and an advanced T-type neutral point clamped (AT-NPC) circuit topology.

4. The three-level converter of claim 1, wherein each of the first, second, and third converter legs comprises first and second transistors connected in series, drain-to-source, between the positive DC node and the negative DC node, and an electrical connection between a drain of the first transistor and a source of the second transistor of each of the first, second, and third converter legs defines an AC voltage node

5. The three-level converter of claim 1, wherein the first converter leg comprises: a first transistor and a second transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the first transistor and a source of the second transistor defining a first leg node; and a third transistor connected in parallel, source-to-drain, with a fourth transistor, such that a first source-to-drain connection is connected to the ground node and a second source-to-drain connection is connected to the first leg node.

6. The three-level converter of claim 5, wherein the second converter leg comprises: a fifth transistor and a sixth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the fifth transistor and a source of the sixth transistor defining a second leg node; and a seventh transistor connected in parallel, source-to-drain, with an eighth transistor, such that a first source-to-drain connection is connected to the ground node and a second source-to-drain connection is connected to the second leg node, and wherein the third converter leg comprises: a ninth transistor and a tenth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the ninth transistor and a source of the tenth transistor defining a third leg node; and an eleventh transistor connected in parallel, source-to-drain, with a twelfth transistor, such that a first source-to-drain connection is connected to the ground node and a second source-to-drain connection is connected to the third leg node.

7. The three-level converter of claim 1, wherein the first converter leg comprises: a first transistor and a second transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the first transistor and a source of the second transistor defining a first leg node; and a first transistor/diode pair including a third transistor connected in parallel, source-to-drain with a first diode, and a second transistor/diode pair including a fourth transistor connected in parallel, source-to-drain, with a second diode, the first transistor/diode pair connected in series with the second transistor/diode pair between the ground node and the first leg node.

8. The three-level converter of claim 7, wherein the second converter leg comprises: a fifth transistor and a sixth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the fifth transistor and a source of the sixth transistor defining a second leg node; and a third transistor/diode pair including a seventh transistor connected in parallel, source-to-drain with a third diode, and a fourth transistor/diode pair including an eighth transistor connected in parallel, source-to-drain, with a fourth diode, the third transistor/diode pair connected in series with the fourth transistor/diode pair between the ground node and the second leg node, and wherein the third converter leg comprises: a ninth transistor and a tenth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the ninth transistor and a source of the tenth transistor defining a third leg node; and a fifth transistor/diode pair including an eleventh transistor connected in parallel, source-to-drain with a fifth diode, and a sixth transistor/diode pair including a twelfth transistor connected in parallel, source-to-drain, with a sixth diode, the fifth transistor/diode pair connected in series with the sixth transistor/diode pair between the ground node and the third leg node.

9. A power conversion system, comprising: an AC power device configured to perform one of receiving AC power to operate the AC power device or generating AC power; and a three-level converter connected to the AC power device, the three-level converter comprising: a first converter leg having first switches connected across a positive DC node and a negative DC node; a second converter leg having second switches connected across the positive DC node and the negative DC node; a third converter leg having third switches connected across the positive DC node and the negative DC node, the first, second, and third converter legs connected to the AC power device to perform one of providing AC power to the AC power device and receiving AC power from the AC power device; and a battery connected between the positive DC node and the negative DC node, and center-connected to a ground node having a ground potential, each of the first, second, and third converter legs connected to the ground node.

10. The power conversion system of claim 9, further comprising: first and second capacitors connected in series between the positive DC node the a negative DC node, a connection of a cathode of the first capacitor and the anode of the second capacitor connected to the ground node.

11. The power conversion system of claim 9, wherein the first, second, and third converter legs are arranged with one of a T-type neutral point clamped (T-NPC) and an advanced T-type neutral point clamped (AT-NPC) circuit topology.

12. The power conversion system of claim 9, wherein each of the first, second, and third converter legs comprises first and second transistors connected in series, drain-to-source, between the positive DC node and the negative DC node, and an electrical connection between a drain of the first transistor and a source of the second transistor of each of the first, second, and third converter legs defines an AC voltage node.

13. The power conversion system of claim 9, wherein the first converter leg comprises: a first transistor and a second transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the first transistor and a source of the second transistor defining a first leg node; and a third transistor connected in parallel, source-to-drain, with a fourth transistor, such that a first source-to-drain connection is connected to the ground node and a second source-to-drain connection is connected to the first leg node.

14. The power conversion system of claim 13, wherein the second converter leg comprises: a fifth transistor and a sixth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the fifth transistor and a source of the sixth transistor defining a second leg node; and a seventh transistor connected in parallel, source-to-drain, with an eighth transistor, such that a first source-to-drain connection is connected to the ground node and a second source-to-drain connection is connected to the second leg node, and wherein the third converter leg comprises: a ninth transistor and a tenth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the ninth transistor and a source of the tenth transistor defining a third leg node; and an eleventh transistor connected in parallel, source-to-drain, with a twelfth transistor, such that a first source-to-drain connection is connected to the ground node and a second source-to-drain connection is connected to the third leg node.

15. The power conversion system of claim 9, wherein the first converter leg comprises: a first transistor and a second transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the first transistor and a source of the second transistor defining a first leg node; and a first transistor/diode pair including a third transistor connected in parallel, source-to-drain with a first diode, and a second transistor/diode pair including a fourth transistor connected in parallel, source-to-drain, with a second diode, the first transistor/diode pair connected in series with the second transistor/diode pair between the ground node and the first leg node.

16. The power conversion system of claim 15, wherein the second converter leg comprises: a fifth transistor and a sixth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the fifth transistor and a source of the sixth transistor defining a second leg node; and a third transistor/diode pair including a seventh transistor connected in parallel, source-to-drain with a third diode, and a fourth transistor/diode pair including an eighth transistor connected in parallel, source-to-drain, with a fourth diode, the third transistor/diode pair connected in series with the fourth transistor/diode pair between the ground node and the second leg node, and wherein the third converter leg comprises: a ninth transistor and a tenth transistor connected in series, drain-to-source, between the positive DC node and the negative DC node, an electrical connection between a drain of the ninth transistor and a source of the tenth transistor defining a third leg node; and a fifth transistor/diode pair including an eleventh transistor connected in parallel, source-to-drain with a fifth diode, and a sixth transistor/diode pair including a twelfth transistor connected in parallel, source-to-drain, with a sixth diode, the fifth transistor/diode pair connected in series with the sixth transistor/diode pair between the ground node and the third leg node.

17. The power conversion system of claim 9, wherein the AC power device is an AC motor that operates based on receiving AC power from the three-level converter.

18. An elevator system, comprising: an elevator car; a motor configured to move the elevator car; a battery for supplying power to the motor; and a three-level converter electrically connected between the battery and the motor to convert DC power from the battery into AC power to run the motor, the three-level converter comprising: a first converter leg having first switches connected across a positive DC node and a negative DC node; a second converter leg having third switches connected across the positive DC node and the negative DC node; a third converter leg having third switches connected across the positive DC node and the negative DC node, wherein the battery is connected between the positive DC node and the negative DC node, and center-connected to a ground node having a ground potential, each of the first, second, and third converter legs connected to the ground node.

19. The elevator system of claim 18, wherein the three-level converter further comprises: first and second capacitors connected in series between the positive DC node and the negative DC node, a connection of a cathode of the first capacitor and the anode of the second capacitor connected to the ground node.

20. The elevator system of claim 18, wherein the first, second, and third converter legs are arranged with one of a T-type neutral point clamped (T-NPC) and an advanced T-type neutral point clamped (AT-NPC) circuit topology.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0018] FIG. 1 is a schematic diagram of a power conversion system including a three-phase three-level converter according to an embodiment of the invention;

[0019] FIG. 2 is a schematic diagram of a power conversion system including a three-phase three-level converter according to another embodiment of the invention; and

[0020] FIG. 3 is an elevator system including a power conversion system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 is a schematic diagram of a power conversion system 100 according to an embodiment of the invention. The system 100 depicted in this embodiment uses a neutral point clamped (NPC) topology having three converter legs, indicated generally by reference letters U, V, and W. The system 100 depicted in this embodiment may be referred to as an advanced T-type neutral point clamped (AT-NPC) circuit. Switches Tu1, Tu2, Tu3, and Tu4 provide a first three-level converter leg (U), switches Tv1, Tv2, Tv3, and Tv4 provide a second three-level converter leg (V), and switches Tw1, Tw2, Tw3, and Tw4 provide a third three-level converter leg (W). In one embodiment, switches Tu1-Tu4, Tv1-Tv4, and Tw1-Tw4 are IGBTs, although MOSFETs, IGCT's, or other similar types of high-voltage switches may be utilized without departing from the scope of the invention.

[0022] When operating as an inverter, the three-level converter legs U, V, and W respectively provide AC power to AC nodes Va, Vb and Vc corresponding to motor winding phases A, B and C of motor 130 as described herein. When operating as rectifier, each three-level converter leg converts an AC voltage applied at one of AC nodes Va, Vb and Vc, to a DC voltage across positive DC node+VDC and negative DC node −VDC.

[0023] Switches Tu1, Tu4, Tv1, Tv4, Tw1, and Tw4 are each associated with a diode, Du1, Du4, Dv1, Dv4, Dw1, and Dw4, respectively. Each diode is connected with its cathode coupled to the collector and its anode coupled to the emitter of a switch, to serve as a freewheeling or flyback diode. The system 100 also includes capacitors C1 and C2, connected such that the anode of capacitor C1 is connected to a positive DC line, the cathode of the capacitor C1 is connected to the anode of the capacitor C2, and the cathode of the capacitor C2 is connected to a negative DC voltage line. A center-grounded battery 101 is illustrated connected to the cathode of capacitor C1 and the anode of the capacitor C2. The battery 101 may provide the DC voltage on the positive and negative voltage lines 102 and 103.

[0024] Also shown in FIG. 1, the system 100 comprises six switches: Tu2 and Tu3 connected source-to-drain in parallel between the nodes N1 and N2; Tv2 and Tv3 connected source-to-drain in parallel between nodes N1 and N3; and Tw2 and Tw3 connected source-to-drain in parallel between nodes N1 and N4.

[0025] When operating as an inverter, a controller (not shown in FIG. 1) applies control signals to switches Tu1-Tu4, Tv1-Tv4, and Tw1-Tw4 to generate AC waveforms at AC nodes Va, Vb and Vc. AC nodes Va, Vb and Vc are coupled to phases A, B, and C of motor 130, which correspond to windings of the motor.

[0026] The power conversion system 100 may also be used as a rectifier to convert AC voltage at AC nodes Va, Vb and/or Vc to a DC voltage across the positive DC node 102 and the negative DC node 103.

[0027] FIG. 2 illustrates a power conversion system 200 according to another embodiment of the invention.

[0028] Similar to the system 100 of the embodiment illustrated in FIG. 1, the system 200 depicted in this embodiment uses a neutral point clamped (NPC) topology having three converter legs, indicated generally by reference letters U, V, and W. The system 200 of FIG. 2 may be referred to as a T-type neutral point claims (T-NPC) circuit. Switches Tu1, Tu2, Tu3, and Tu4 provide a first three-level converter leg (U), switches Tv1, Tv2, Tv3, and Tv4 provide a second three-level converter leg (V), and switches Tw1, Tw2, Tw3, and Tw4 provide a third three-level converter leg (W). In one embodiment, switches Tu1-Tu4, Tv1-Tv4, and Tw1-Tw4 are IGBTs, although MOSFETs, IGCT's, or other similar types of high-voltage switches may be utilized without departing from the scope of the invention.

[0029] When operating as an inverter, the three-level converter legs U, V, and W respectively provide AC power to AC nodes Va, Vb and Vc corresponding to motor winding phases A, B and C of motor 230 as described herein. When operating as rectifier, each three-level converter leg converts an AC voltage applied at one of AC nodes Va, Vb and Vc, to a DC voltage across positive DC node 202 and negative DC node 203.

[0030] Switches Tu1, Tu4, Tv1, Tv4, Tw1, and Tw4 are each associated with a diode, Du1, Du4, Dv1, Dv4, Dw1, and Dw4, respectively. Each diode is connected with its cathode coupled to the collector and its anode coupled to the emitter of a switch, to serve as a freewheeling or flyback diode. The system 200 also includes capacitors C1 and C2, connected such that the anode of capacitor C1 is connected to the positive DC node 202, the cathode of the capacitor C1 is connected to the anode of the capacitor C2, and the cathode of the capacitor C2 is connected to the negative DC node 203. A center-grounded battery 201 is illustrated connected to the cathode of capacitor C1 and the anode of the capacitor C2. The battery 201 may provide the DC voltage on the positive and negative nodes 102 and 103.

[0031] Also shown in FIG. 2, the system 200 comprises six diode-switch pairs. The first pair 211 includes switch Tu2 connected in parallel with diode Du2, and the second pair 212 includes switch Tu3 connected in parallel with diode Du3. The first and second pairs are connected in series between node N1 and node N2. The third pair 213 includes switch Tv2 connected in parallel with diode Dv2, and the fourth pair 214 includes switch Tv3 connected in parallel with diode Dv3. The third and fourth pairs are connected in series between node N1 and node N3. The fifth pair 215 includes switch Tw2 connected in parallel with diode Dw2, and the sixth pair 216 includes switch Tw3 connected in parallel with diode Dw3. The fifth and sixth pairs are connected in series between node N1 and node N4.

[0032] When operating as an inverter, a controller (not shown in FIG. 2) applies control signals to switches Tu1-Tu4, Tv1-Tv4, and Tw1-Tw4 to generate AC waveforms at AC nodes Va, Vb and Vc. AC nodes Va, Vb and Vc are coupled to phases A, B, and C of motor 130, which correspond to windings of the motor.

[0033] The power conversion system 100 may also be used as a rectifier to convert AC voltage at AC nodes Va, Vb and/or Vc to a DC voltage across the positive DC node 202 and the negative DC node 203.

[0034] While embodiments of the invention encompass any system, device, or assembly requiring power conversion, in one embodiment the power conversion system is implemented in a battery-powered elevator system. FIG. 3 illustrates a block diagram of a battery-powered elevator system according to an embodiment of the invention. The system 300 includes a battery 301. The battery 301 may be a center-grounded battery, such as the battery 101 of FIG. 1 or the battery 201 of FIG. 2. The elevator system 300 includes a 3-level converter system 302, such as the system 100 illustrated in FIG. 1 or the system 200 illustrated in FIG. 2, between the battery 301 and a motor 303. The motor 303 is connected to an elevator car 304 to move the elevator car 304. In addition, the motor 303 may be configured to generate AC power based on movement of the elevator car 304, such as by the descent of the elevator car 304 to provide regenerative power in the elevator system 300. In such an embodiment, the power provided by the motor 303 based on movement of the elevator car 304 is provided to the three-level converter system 302, where it is converted to DC power and supplied to the battery 301 to charge the battery. The block diagram of FIG. 3 illustrates a basic functional structure of an elevator system 300 according to an embodiment of the invention, but embodiments of the invention are not limited to the illustrated structure. Instead, embodiments encompass any elevator system utilizing a three-level converter.

[0035] Technical effects of embodiments of the invention having 3-level power conversion include providing power conversion utilizing lower voltages and less electromagnetic interference compared to conventional power converters, such as half-bus switched power converters.

[0036] Embodiments provide benefits over existing designs. The use of a battery center-connected to a ground node means there is no need for a control effort to ensure neutral point stability. As the switches no longer are used to control stability of the neutral point, the system can be operated with minimized switching to achieve lower EMI, to achieve lower acoustic noise from motor and to achieve lower current ripple in motor, and hence less heating. The ability to apply a discontinuous PWM (e.g., 2 out of 3 switching) technique provides further efficiency in power conversion in the inverter, and allows other efficiencies as one degree of freedom in the control can be used for other purposes. The NPC type topology allows use of more common, lower voltage rating devices (<100V). Embodiments are efficient as a charger. A charger design using, for example, the topology of FIG. 2 achieves efficient charging, with lower EMI.

[0037] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.