Uninterruptible Power Supply System

Abstract

The present invention relates to an uninterruptible power supply system, comprising: at least one AC input terminal (3); an AC output terminal (2) and a DC input terminal (4); at least one uninterruptible power supply UPS device (1, N), the at least one uninterruptible power supply UPS device (1, N) comprising a DC link (7), a DC / AC converter (9) connected to the DC link (7) on a first side and to the AC output terminal (2) on a second side, and a DC / DC converter (11) connected to the DC input terminal (4) on a first side and to the DC link (7) on a second side; and at least two switches (8) and at least one coupled differential mode inductor (12) having two windings (10), whereby each switch (8) is connected in series with at least one winding (10) to form a series connection (6), and the series connection (6) is connected to at least one AC input terminal (3) on a first side and to the AC output terminal (2) on a second side.

Description

Technical Field

[0001] The present invention relates to an uninterruptible power supply system, comprising: at least one AC input terminal, an AC output terminal and a DC input terminal; at least one uninterruptible power supply UPS, comprising a DC link, a DC / AC converter connected to the DC link on a first side and to the AC output terminal on a second side, and a DC / DC converter connected to the DC input terminal on a first side and to the DC link on a second side. Background Art

[0002] Power quality events in electrical installations are a significant issue. These events include any type of disturbance in the AC source, ranging from single-phase drops (sags) or failures to outages of a polyphase AC source. To handle power quality events, uninterruptible power supply units and systems provide an uninterruptible power supply (UPS) to the load.

[0003] A typical UPS system and / or UPS device, respectively, includes an AC / DC converter, also known as a rectifier, and an output DC / AC converter, also known as an inverter. The AC / DC converter and the DC / AC output converter are interconnected via a DC link having positive and negative busbars and / or rails or simply a link. The DC link typically has a midpoint reference, a positive reference, and a negative reference, connected via two capacitors arranged in series. The rectifier is typically implemented as a half-bridge boost converter, maintaining regulation relative to an internal and / or source reference (e.g., typically source neutral) via the positive and negative rails of the DC link. Furthermore, the AC / DC converter is connected to an AC source on the source side of the UPS, and the DC / AC output converter is connected to a load, typically an AC load, on the load side of the UPS. Furthermore, the UPS includes an additional DC / DC converter (also known as a battery converter) and a DC source, whereby the DC / DC converter connects the DC source to the DC link. The DC source is typically a battery, which is charged from the DC link via the DC / DC converter. Each UPS device in such a UPS system may be connected to an individual battery, or the UPS devices in the UPS system may share a single battery or multiple batteries. One or more batteries may be an integral part of the UPS device or UPS system, or they may be provided separately. In either case, the operation of the UPS device or UPS system does not change, as this is more of a limiting issue.

[0004] Today's UPS systems often feature a modular approach, allowing for a very flexible and robust approach to system construction. This makes system growth easily accommodated, both for redundancy and maintainability, or overall reliability. Since converters are inherently current-controlled devices, load sharing is typically perfectly controlled to a precision that is not an issue for individual drive systems (i.e., UPS units operating in parallel). This distributed architecture is an attractive alternative for bypassing UPS systems, particularly for large systems where high short-circuit currents and letthrough energy are essential.

[0005] However, due to the nature of commonly used semiconductor devices, current sharing can pose a problem in silicon-controlled rectifiers (SCRs), also known as thyristors. It's important to note that such devices are typically naturally commutated and therefore cannot easily operate as converters within line cycles such as 50 / 60 Hz. Due to structural tolerances and material properties, the current sharing of these parallel devices depends on inherent variations within the semiconductors. Parameters influencing current sharing can include threshold voltage, forward voltage, forward slope resistance, fall time, forward recovery time, and temperature coefficient, among others. For example, variations in forward voltage (Vf) and threshold voltage (Vt) play a relevant role in current sharing between devices, as devices with higher currents due to lower Vf will run hotter and therefore conduct a greater share of the total current due to the negative Vf coefficient of their silicon structure. Other differences in the physical structure of the UPS system, external to the semiconductor devices, can further affect current sharing within the semiconductors. These differences can include imbalances in passive current paths, temperature variations between devices, gating delays and amplitude differences between devices, and overall wiring impedance mismatches.

[0006] Distributed bypass is a common practical solution used in UPS systems. The bypass drive system is typically housed in a UPS unit that also houses the converter, whereby each UPS unit is typically provided as a complete UPS consisting of a conventional AC-DC-AC converter (i.e., rectifier) with a converter and inverter (as described above) and a bypass for energy storage. However, with this approach, current sharing in bypass mode is a known problem for UPS systems built with a balance, for example by compensating a certain point with impedances between modules. The size of the UPS system, i.e., the number of UPS units, increases this problem and tends to get worse in unpredictable ways. An alternative approach is to house the parallel bypass drive systems in separate assemblies, but the current sharing problem still persists or may actually become more severe due to the reduction in overall wiring through a more compact system build. Summary of the Invention

[0007] It is therefore an object of the present invention to provide an improved solution to current sharing between parallel UPS devices in a UPS system.

[0008] The objects of the invention are solved by the features of the independent claims. Preferred embodiments are specified in the dependent claims.

[0009] Therefore, the object is solved by an uninterruptible power supply system comprising

[0010] at least one AC input terminal, an AC output terminal and a DC input terminal,

[0011] At least one uninterruptible power supply (UPS) device, including

[0012] DC link

[0013] a DC / AC converter connected on a first side to the DC link and on a second side to the AC output terminals, and

[0014] a DC / DC converter connected on a first side to the DC input terminals and on a second side to the DC link, and

[0015] At least two switches and at least one coupled differential mode inductor having two windings, whereby

[0016] Each switch is connected in series with at least one winding to form a series connection, and

[0017] The series connection is connected on a first side to at least one AC input terminal and on a second side to an AC output terminal.

[0018] Therefore, a key point of the present invention is to provide a very cost-effective, scalable and redundant bypass structure for a UPS system by connecting a switch in series with at least one winding of at least one coupled differential-mode inductor. The bypass thus provided takes into account the current sharing between parallel UPS devices in the UPS system, thereby providing a robust, passively controlled, fault-tolerant, and especially inherently reliable and accurate current sharing for a distributed bypass architecture, especially when divided with three or more UPS devices. The series connection thus compensates for possible current imbalances between parallel UPS devices by the current imbalances caused by the magnetically coupled windings of the coupled differential-mode inductors. Therefore, each coupled differential-mode inductor is connected to two different switches via its two windings. The UPS device preferably includes a DC link (optionally including an AC / DC converter), a DC / AC converter, and a DC / DC converter.

[0019] A UPS system may have a stored energy source, commonly referred to as a "battery", to maintain the DC link in the event of an abnormal condition of the AC source, so that load support through the second converter assembly can be maintained without interruption. The battery is typically connected to the DC link through a DC / DC converter to account for voltage changes in the battery due to depletion or other characteristics. The battery is not limited to ordinary VRLA, it can be any practical DC source, including fuel cells, photovoltaics, wind power or other. Multiple DC / DC converters can be connected to the DC link and run in parallel to support the DC link. For maximum simplicity, the connection to the battery is preferably two wires. The connection of the battery and\or DC source to the DC link and its common internal reference / neutral line can take several forms, such as only linking the positive and negative terminals or only linking to one of the link and neutral line. The load can be an AC load, a DC load or a combination thereof and / or a multi-phase load.

[0020] Preferably, the AC / DC converter, DC / AC converter, and / or DC / DC converter are operated using an interleaved mode with pulse-width PWM modulation or PWM phase shifting. PWM has the advantage of requiring less control power, while interleaving facilitates optimization of, for example, filter ripple. Preferably, multiple DC / AC converters and / or DC / DC converters are provided. The AC / DC converter, DC / AC converter, and / or DC / DC converter preferably comprise Si, SiC, and / or GaN semiconductors. Such semiconductors are characterized by improved performance, as the materials allow for efficient operation, particularly in a two-stage topology with a much simpler overall construction. SiC and / or GaN semiconductors have significantly lower switching losses than conventional Si semiconductors. Therefore, in addition to discontinuous current mode (DCM), operation in permanent constant current mode (CCM) may also be advantageous. In this mode, the slope of the current is typically allowed to return to zero before the next switching event, thereby significantly reducing overall losses. The modes can be adopted and varied on an adaptive basis depending on load level and short- and long-term stress considerations, with the potential energy throughput generally being higher in CCM.

[0021] In a preferred embodiment, the switch includes and / or is provided as a thyristor, a gate turn-off thyristor (GTO), an insulated gate bipolar transistor (IGBT), an integrated gate commutated thyristor (IGCT), a field effect transistor (FET), a contactor, a relay, a switch, a pluggable contact and / or plug, a mechanical switch, or any other possible switching method. In an alternative embodiment, the switch can be replaced by an electronically controlled and / or manually operated contact, or have parallel and / or serial electronically controlled and / or manually operated contacts, such as, but not limited to, contactors, relays, switches, pluggable contacts, and / or plugs.

[0022] According to another preferred embodiment, the switch is provided as a semiconductor module with controlled current commutation and / or includes a protection device, a controlled disconnection device, and / or a measuring device connected in series with at least one winding. The protection device is preferably provided as a fuse and / or the controlled disconnection device is preferably provided as a contactor and / or any other electrical and / or mechanical switching device, such as, for example, an IGBT, a GTO, and / or an IGCT. The measuring device is preferably connected to a control device as described below and / or to the controlled disconnection device. In this way, for example, if the current measured by the measuring device exceeds a threshold value, the control device can open the series connection by actuating the controlled disconnection device.

[0023] In another preferred embodiment, the uninterruptible power supply system includes at least N switches and at least N, N-1, or N-2 coupled differential-mode inductors, each having two windings, where N is an integer and ≥ 2, whereby at least two windings of at least two different coupled differential-mode inductors are connected in series. Thus, at least two windings of separate, different coupled differential-mode inductors are connected in series with each current-commutated semiconductor module. The coupled windings of at least two coupled differential-mode inductors in series particularly improve current sharing because the circular connection essentially solves the aforementioned problems.

[0024] According to another preferred implementation, an uninterruptible power supply system includes at least N switches and at least N, N-1, or N-2 coupled differential-mode inductors, each having two windings, where N is an integer and ≥ 3, such that each of the at least N, N-1, or N-2 different coupled differential-mode inductors has at least N, N-1, or N-2 windings connected in series. Because the first and last lines have the impedance of the other lines, this implementation allows for even distribution of line impedance among the switches. Furthermore, because a failure of one switch inhibits current balancing among the other switches, the use of at least two coupled differential-mode inductors coupled in series can provide single fault tolerance. For example, there may be four switches, two coupled differential-mode inductors, and one winding (i.e., no series connection of windings from different coupled differential-mode inductors), while in another case, there may be four switches, four coupled differential-mode inductors, and two windings each connected in series. In another case, there may be four switches, 16 coupled differential-mode inductors with eight windings connected in series.

[0025] In a further preferred embodiment, at least one uninterruptible power supply (UPS) device comprises an AC / DC converter connected on a first side to at least one AC input terminal and on a second side to a DC link. With such an AC / DC converter, the system can be operated online, and in an alternative topology without an AC / DC converter, offline operation is possible as a whole, so that the link support and the stored energy charge are performed by the reverse-operated DC / AC converter. The series connection is connected on a first side to at least one AC input terminal and on a second side to the AC output terminal. This means, for example, that the series connection can be connected in parallel to the UPS device, between the AC input terminal and the AC / DC converter, or between the DC / AC converter and the AC output terminal.

[0026] According to another preferred embodiment, the uninterruptible power supply system includes two, three, or more phases. Preferably, each phase includes at least one series connection formed by a switch and at least one winding connected in parallel. In another preferred embodiment, at least one AC input terminal and / or AC output terminal is provided as a busbar. The busbar is preferably a mounting point for power inlet, for example, for connecting an AC source to an outlet for connecting a load.

[0027] In another preferred embodiment, the uninterruptible power supply system includes a plurality of at least two switches and at least one coupled differential mode inductor, each having two windings connected in parallel. In another preferred embodiment, the series connection is integrated into the UPS device as a bypass or is external to the UPS device. In this way, the series connection can be placed outside the UPS device, for example, in the current path between the DC / AC converter and / or the AC output terminals and the load. Placement within the UPS device means, for example, at least in parallel with the DC / AC converter.

[0028] According to another preferred implementation, the uninterruptible power supply system comprises at least two AC input terminals and at least three or four series connections, whereby at least every two series connections are connected to each of the at least two AC input terminals.

[0029] In another embodiment, the uninterruptible power supply system includes a control device configured to control the UPS system. The control device is preferably provided as a computerized component, for example as a correspondingly programmed microprocessor. The control device can be associated with each UPS and / or UPS device or with the UPS system, thereby controlling each UPS device of the UPS system. The control device can include a user interface, or the UPS system can include a system-level user interface. In addition, the control device can include a communication component for communicating with other control devices and / or external devices. In a preferred embodiment of the UPS, the control device is configured to operate the AC / DC converter, the DC / AC converter and / or the DC / DC converter using an interleaved mode with pulse width PWM modulation or PWM phase shift. According to another preferred embodiment, at least two parallel DC / DC converters are provided, and the control device is configured to operate the at least two DC / DC converters in parallel or in a time-interleaved manner for controlling energy extraction from multiple DC sources.

[0030] In another preferred embodiment, the coupled differential mode inductor is provided as a transformer. Generally, the coupled differential mode inductor cancels the magnetic flux within the inductor's ferrite core, so that no impedance is generated for differential mode currents and magnetic saturation issues are minimal. Coupled differential mode inductors are also referred to as differential mode chokes and / or coils. The coupled differential mode inductor preferably includes two coils and / or windings wound around a single core, whereby the windings are negatively coupled to cancel the magnetic flux generated by the differential mode DM current. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] These and other aspects of the invention will be apparent from and elucidated with reference to the implementations described hereinafter.

[0032] In the attached figure:

[0033] Figure 1 A schematic diagram shows an uninterruptible power supply UPS system according to a preferred implementation.

[0034] Figure 2 A first preferred implementation is shown in schematic form with four switches and two coupled differential mode inductors,

[0035] Figure 3 A second preferred implementation is shown in schematic form with three switches and three coupled differential mode inductors,

[0036] Figure 4 A third preferred implementation is shown in schematic form with four switches and four coupled differential mode inductors,

[0037] Figure 5 A fourth preferred implementation is shown schematically with four switches and four coupled differential mode inductors, and

[0038] Figure 6 A fifth preferred implementation with five switches and five coupled differential mode inductors is shown in the form of three schematic diagrams. DETAILED DESCRIPTION

[0039] Figure 1 A schematic diagram illustrates an uninterruptible power supply (UPS) system according to a preferred implementation. The UPS system comprises a plurality of identical UPS devices, two of which are shown, referred to as UPS 1 and UPS N. The UPS system includes at least one AC output terminal 3 for connection to an AC source 3; an AC input terminal 2 for connection to a load; and at least one DC input terminal 4 for connection to at least one DC source 4.

[0040] Each UPS device 1, N includes an AC / DC converter 5, which is implemented as an AC / DC rectifier and includes at least two independently controlled first converters (not shown). The AC / DC converter 5 is connected on a first side to at least one AC terminal 3 and on a second side to a DC link 7, which includes two halves with a midpoint reference (not shown). Each UPS device 1, N also includes a DC / AC converter 9, which is implemented as an inverter and includes an independently controlled second converter, which is implemented as a DC / AC inverter (not shown). The DC / AC converter 9 is connected on a first side to the DC link 7 and on a second side to the AC output terminal 2. Figure 1 A further DC / AC converter 9 is shown, connected in parallel to the DC / AC converter 9. Alternatively, the AC / DC converter 5 may be omitted, and the link support and stored energy charge may be done by the DC / AC converter 9 operating in reverse.

[0041] Each UPS device 1, N even includes at least one DC / DC converter 11, and the two DC / DC converters 11 are Figure 1 1 and are connected in parallel. Each of the two DC / DC converters 11 includes an independently controlled third converter, which is connected to the DC source 4 on a first side via the DC input terminals 4 and to the DC link 7 on a second side. The third DC / DC converter 11 is provided as an energy converter for DC / DC storage with a corresponding third converter. The UPS system or each UPS device 1, N also includes a computerized control device 13, which includes a user interface and communication means for communicating with an optional UPS system-level user interface 14. The first converter, the second converter and the third converter include Si, SiC and / or GaN semiconductors.

[0042] Now also refer to Figures 2 to 6 , the UPS system comprises at least one bypass 6 between the AC input terminal 3 and the AC output terminal 2, which is provided as a series connection 6 of a switch 8 and one winding 10 of a coupled differential mode inductor 12. By now referring to Figure 2 In the implementation shown in FIG, the UPS system includes two AC input terminals 3 and one AC output terminal 2, and Figures 3 to 6 The implementation in includes only one AC input terminal 3. For simplicity reasons, Figures 2 to 6 Converters 5, 9 and 11 are not shown.

[0043] exist Figure 2, two coupled differential-mode inductors 12, each having two windings 10, are connected in parallel on one side to the AC output terminal 2. Each winding 10 of the two coupled differential-mode inductors 12 is connected in series with one of the four switches 8 to the AC input terminal 3, such that every two switches 8 are connected to one of the two AC input terminals 3. The series connection 6 of the switches 8 and the coupled differential-mode inductors 12 compensates for possible current imbalances between the parallel UPS devices 1, N by magnetically induced current imbalances by the coupled balanced voltages in the windings 10 of the coupled differential-mode inductors 12.

[0044] Each of the four switches 8 comprises a silicon controlled rectifier SCR 15, in particular as a pair of anti-parallel thyristors 15 connected in parallel. Alternatively, the switch 8 comprises a thyristor, a gate turn-off thyristor GTO, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, a field effect transistor FET, a contactor, a relay, a switch, a pluggable contact and / or a plug, as in Figure 4 The mechanical switch shown in or any other possible switching components.

[0045] Figure 3 Another implementation is shown with three switches 8 and three coupled differential-mode inductors 12, whereby each switch 8 is connected in series with two windings 10 of two different coupled differential-mode inductors 12. Each switch 8 includes, in addition to a pair of anti-parallel thyristors 15 connected in parallel, a protection device 16, i.e., a fuse; a controlled disconnection device 17, i.e., a mechanical and / or electrical switch; and a current measuring device 18, all of which are connected in series with the parallel-connected pair of anti-parallel thyristors and / or windings 10. The controlled disconnection device 17 and the current measuring device 18 are connected to the control device 13.

[0046] Figure 4 Another implementation is shown having four switches 8 , each provided as a mechanical switch, and four coupled differential mode inductors 12 , whereby each switch 8 is connected in series with two windings 10 of two different coupled differential mode inductors 12 . Figure 5 A similar implementation is shown, but with pairs of anti-parallel thyristors 15 connected in parallel instead of mechanical switches.

[0047] at last, Figure 6The dotted lines illustrate the magnetic coupling of paired windings 10 through coupled differential-mode inductors 12. Starting with the left-hand implementation, all five switches 8 are conducting, resulting in magnetic coupling in all five coupled differential-mode inductors 12. Turning now to the upper-right implementation, the middle current-commutated semiconductor module 8 is non-conducting, while all other current-commutated semiconductor modules 8 are conducting. Thus, the second coupled differential-mode inductor 12 from the top is not magnetically coupled. Thus, the two highest current-commutated semiconductor modules 8 and the two lowest current-commutated semiconductor modules 8 remain coupled. Turning to the lower-right implementation, the third and fifth current-commutated semiconductor modules 8 from the top are both non-conducting. Thus, the second and fifth coupled differential-mode inductors 12 do not provide magnetic coupling. In this case, current balancing is no longer achieved. However, by connecting the current-commutated semiconductor modules 8 to a matrix consisting of N*N coupled differential-mode inductors 12, where N is a positive natural number, current balancing can be achieved even in this case.

[0048] Although the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention, by studying the drawings, the present disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0049] Reference Symbols List

[0050] 1. N UPS device

[0051] 2 Load, AC output terminals

[0052] 3 AC source, AC input terminal

[0053] 4 DC source, DC input terminals

[0054] 5 AC / DC converter

[0055] 6 Bypass, series connection

[0056] 7 DC Link

[0057] 8 switches, semiconductor modules for controlled current commutation

[0058] 9 DC / AC converter

[0059] 10 windings

[0060] 11 DC / DC converter

[0061] 12 Coupled differential mode inductors

[0062] 13 Control Device

[0063] 14 User Interface

[0064] 15 Silicon controlled rectifier, a pair of anti-parallel thyristors connected in parallel

[0065] 16 Protective devices

[0066] 17 Controlled disconnect device

[0067] 18. Measuring device.

Claims

1. An uninterruptible power supply system, comprising at least one AC input terminal (3), an AC output terminal (2) and a DC input terminal (4), At least one uninterruptible power supply UPS device (1, N) comprising DC link (7), a DC / AC converter (9) connected on a first side to the DC link (7) and on a second side to the AC output terminals (2), a DC / DC converter (11) connected on a first side to the DC input terminals (4) and on a second side to the DC link (7), at least two switches (8) and at least one coupled differential mode inductor (12) having two windings (10), whereby each switch (8) is connected in series with at least one winding (10), thereby forming a series connection (6), The series connection is integrated into the at least one UPS device (1, N) as a bypass of the at least one UPS device (1, N), and The series connection (6) is connected on a first side to the at least one AC input terminal (3) and on a second side to the AC output terminal (2).

2. The uninterruptible power supply system according to claim 1, wherein the switch (8) comprises a thyristor, a GTO, an IGBT, an IGCT, a FET, a pair of anti-parallel thyristors (15) connected in parallel, a contactor, a relay, a switch, a pluggable contact and / or a plug.

3. An uninterruptible power supply system according to claim 1 or 2, whereby the switch (8) is provided as a semiconductor module with controlled current commutation and / or comprises a protection device (16), a controlled disconnection device (17) and / or a measuring device (18) connected in series with the at least one winding (10).

4. The uninterruptible power supply system according to claim 1 or 2, comprising: At least N switches (8) and at least N, N-1 or N-2 coupled differential mode inductors (12), each of the coupled differential mode inductors (12) having two windings (10), where N is an integer and ≥2, whereby at least two windings (10) of at least two different coupled differential mode inductors (12) are connected in series.

5. The uninterruptible power supply system according to claim 1 or 2, comprising at least N switches (8) and at least N, N-1 or N-2 coupled differential mode inductors (12), each of the coupled differential mode inductors (12) having two windings (10), wherein N is an integer and ≥3, whereby each of the at least N, N-1 or N-2 windings (10) of the at least N, N-1 or N-2 different coupled differential mode inductors (12) are connected in series.

6. An uninterruptible power supply system according to claim 1 or 2, whereby the at least one uninterruptible power supply UPS device (1, N) comprises an AC / DC converter (5) connected on a first side to the at least one AC input terminal (3) and on a second side to the DC link (7).

7. The uninterruptible power supply system according to claim 1 or 2, comprising two, three or more phases.

8. The uninterruptible power supply system according to claim 1 or 2, whereby the at least one AC input terminal (3) and / or the AC output terminal (2) are provided as busbars.

9. The uninterruptible power supply system according to claim 1 or 2, comprising a plurality of at least two switches (8) and at least one coupled differential mode inductor (12), each of the coupled differential mode inductors (12) having two windings (10) connected in parallel.

10. The uninterruptible power supply system according to claim 1 or 2, comprising: At least two AC input terminals (3) and at least four series connections (6), whereby at least every two series connections (6) are connected to each of the at least two AC input terminals (3).

11. The uninterruptible power supply system according to claim 1 or 2, comprising a control device (13) configured to control the UPS system.

12. The uninterruptible power supply system according to claim 1 or 2, whereby the coupled differential mode inductor (12) is provided as a transformer.

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