UPS system for powering alternating and direct current loads

Methods, systems, and apparatus, for powering AC and DC loads in the event of a power failure. In one aspect, a system includes one or more DC loads that are powered by DC power, one or more AC loads that are powered by AC power, and an uninterruptible power supply (UPS). The UPS includes AC terminals connected to an AC power source and to the one or more AC loads to power the AC loads, DC terminals connected to a backup battery and to the one or more DC loads to power the DC loads a bidirectional AC/DC converter connected between the AC terminals and the DC terminals, and a controller that selectively switches the bidirectional AC/DC converter to the first mode when the AC power source is available and to the second mode when the AC power source is not available.

BACKGROUND

Uninterruptible power supplies (UPSs) are used in mission critical applications to provide continuous power in case of a power failure event. In general, there are two types of UPS systems, direct current (DC) UPSs and alternating current (AC) UPSs. A DC UPS is used to provide DC power to DC loads. An AC UPS is used to provide AC power to AC loads. Both types of UPSs can provide the backup power from batteries or other stored power sources, such as capacitors.

In a typical AC UPS system, the backup battery is a higher voltage battery than for DC UPS systems. In general, a DC UPS is not compatible with an AC UPS. Thus, different types of UPS systems need to be used in order to supply power to both AC and DC loads.

SUMMARY

This specification describes technologies relating to UPS systems that provide power to both AC and DC loads.

In general, one innovative aspect of the subject matter described in this specification can be embodied in systems that include one or more direct current (DC) loads that are powered by DC power, one or more alternating current (AC) loads that are powered by AC power, and an uninterruptible power supply (UPS) that includes AC terminals connected to an AC power source and to the one or more AC loads to power the AC loads, DC terminals connected to a backup battery and to the one or more DC loads to power the DC loads, a bidirectional AC/DC converter connected between the AC terminals and the DC terminals and that operates in a first mode in which the bidirectional AC/DC converter converts AC power received at the AC terminals to DC power and provides the DC power at the DC terminals, wherein the DC power at the DC terminals charges the backup battery and powers the one or more DC loads; and a second mode in which the bidirectional AC/DC converter converts DC power received at the DC terminals to AC power and provides the AC power at the AC terminals, wherein the AC power at the AC terminals powers the one or more AC loads; and a controller that selectively switches the bidirectional AC/DC converter to the first mode when the AC power source is available and to the second mode when the AC power source is not available. Other embodiments of this aspect include corresponding methods and apparatus.

These and other implementations can each optionally include one or more of the following features. In some aspects, the backup battery provides the DC power at the DC terminals when the bidirectional AC/DC converter is operating in the second mode. The backup battery can also provide DC power to the one or more DC loads when the bidirectional AC/DC converter is operating in the second mode. In some aspects, the AC power source is connected to the one or more AC loads and provides AC power to the one or more AC loads when the bidirectional AC/DC converter is operating in the first mode.

Some aspects include a switch connected between the AC power source and (i) the AC power terminals and (ii) the one or more AC loads. The controller can close the switch when the bidirectional AC/DC converter is operating in the first mode and opens the switch when the bidirectional AC/DC converter is operating in the second mode.

In some aspects, the UPS includes a bidirectional DC/DC converter connected between the AC/DC converter and the DC terminals. In some aspects, when the AC/DC converter is operating in the second mode, the bidirectional DC/DC converter steps up a voltage of the DC power at the DC terminals for input to the bidirectional AC/DC converter and when the AC/DC converter is operating in the first mode, the bidirectional DC/DC converter steps down an output voltage of the bidirectional AC/DC converter.

In general, another aspect of the subject matter described in this specification can be embodied in a UPS that includes AC terminals configured to connect to an AC power source and to one or more AC loads, DC terminals configured to connect to a backup battery and to one or more DC loads, a bidirectional AC/DC converter connected between the AC terminals and the DC terminals and that operates in: a first mode in which the bidirectional AC/DC converter converts AC power received at the AC terminals to DC power and provides the DC power at the DC terminals for charging the backup battery and powering the one or more DC loads; and a second mode in which the bidirectional AC/DC converter converts DC power received at the DC terminals to AC power and provides the AC power at the AC terminals for powering the one or more AC loads; and a controller that selectively switches the bidirectional AC/DC converter to the first mode when the AC power source is available and to the second mode when the AC power source is not available. Other embodiments of this aspect include corresponding methods and apparatus.

In some aspects, the backup battery provides the DC power at the DC terminals when the bidirectional AC/DC converter is operating in the second mode. The backup battery can also provide DC power to the one or more DC loads when the bidirectional AC/DC converter is operating in the second mode.

In some aspects, the AC power source is connected to the one or more AC loads and provides AC power to the one or more AC loads when the bidirectional AC/DC converter is operating in the first mode.

In some aspects, the AC power terminals are configured to connect to a first terminal of a switch that has a second terminal that is connected to the AC power source. The controller can be configured to close the switch when the bidirectional AC/DC converter is operating in the first mode and open the switch when the bidirectional AC/DC converter is operating in the second mode.

In some aspects, the UPS includes a bidirectional DC/DC converter connected between the AC/DC converter and the DC terminals. In some aspects, when the AC/DC converter is operating in the second mode, the bidirectional DC/DC converter steps up a voltage of the DC power at the DC terminals for input to the bidirectional AC/DC converter and when the AC/DC converter is operating in the first mode, the bidirectional DC/DC converter steps down an output voltage of the bidirectional AC/DC converter.

The subject matter described in this specification can be implemented in particular embodiments so as to realize one or more of the following advantages. A single UPS system described in this document can provide power to both AC and DC loads simultaneously in the event of a power failure. Using a single UPS system rather than one for each type of load results in more compact systems, more space for other components, and reduced costs. For example, in a data center environment, a UPS system that can power both types of loads can reduce the amount of rack space required for the UPS system, allowing for more computing components to be installed in each rack. In addition, only one type of power has to be provided to each rack, reducing the complexity of power routing systems that route power to the racks and reducing the number of cables routed to the racks.

Various features and advantages of the foregoing subject matter is described below with respect to the figures. Additional features and advantages are apparent from the subject matter described herein and the claims.

DETAILED DESCRIPTION

In general, this document describes technologies relating to UPS systems that can provide power to DC and AC loads in the event of a power failure. Power failures can include loss of input power for the loads, power sags, power surges, under voltage conditions, over voltage conditions, noise on the power line, frequency variation, switching transients, harmonics, or other conditions that cause a UPS to power the loads until the input power returns to normal.

The UPS system can include a bidirectional AC/DC converter that, in one mode, converts AC power to DC power and, in another mode, converts DC power to AC power. In one direction in a first mode, the bidirectional AC/DC converter can act as a rectifier converting AC power to DC power. In a second direction in a second mode, the bidirectional AC/DC converter can act as an inverter converting DC power to AC power. A controller can selectively switch the bidirectional AC/DC converter between the first and second modes depending on whether there is a power failure of the input power for the loads.

An AC power source can be connected to AC terminals of the UPS. The AC terminals can be connected to the AC side of the bidirectional AC/DC converter. The AC power source and the AC terminals can also be connected to one or more AC loads. DC terminals of the UPS system can be connected to one or more backup batteries and to one or more DC loads. The DC terminals can be connected to the DC side of the bidirectional AC/DC converter, e.g., by way of an optional DC/DC converter of the UPS.

In normal operation when the AC power source is available, the AC power source can provide power to the UPS system and the AC loads. The bidirectional AC/DC converter can operate in the first mode in which it converts the AC power received at the AC terminals to DC power provided at the DC terminals. This DC power can charge the backup batteries and power the DC load(s).

When there is a power failure, the bidirectional converter can operate in the second mode. In this mode, the batteries provide DC power to the DC load(s) and to the DC terminals of the UPS. The bidirectional AC/DC converter converts the DC power to AC power provided at the AC terminals. This AC power provided at the AC terminals powers the AC load(s) during the power failure. Thus, the UPS and backup batteries provide power to the AC and DC loads during a power failure.

FIG. 1is a block diagram of an environment100in which an example UPS system provides power to DC and AC loads in the event of a power failure. The environment100includes a UPS architecture in which the UPS system powers both DC and AC loads in the event of a power failure. In this example, the UPS system provides continuous power to one or more DC loads140and one or more AC loads120of a data center rack105in the event of a power failure of an input AC power source160.

The DC load(s)140can include loads that are normally powered by DC input power, e.g., 12 VDC loads. The AC load(s)130can include loads that are powered by AC input power, e.g., 120 VAC input power. For example, in a data center, the AC loads130can include off the shelf equipment that plugs into a standard AC outlet, e.g., a standard 120 VAC outlet, although the equipment actually runs off of DC power. That is, the equipment may include an internal AC/DC converter that converts the AC power to DC power for the equipment. The DC loads in a data center can include equipment that is powered directly by DC power.

The UPS system can include a UPS120and one or more backup batteries150. The UPS120is connected to AC power lines122that connect the AC power source160to the AC load(s)130and the UPS120. The UPS120is also connected to DC power lines124that also connect to the DC load(s)140and the backup batteries150. Although shown as two different components, the batteries150can be part of the UPS120, e.g., included in the same housing at the rest of the UPS120.

As described in more detail with reference toFIG. 2, the UPS120can include a bidirectional AC/DC converter. The AC side of the bidirectional AC/DC converter can be connected to the AC power lines122and the DC side of the bidirectional AC/DC can be connected to the DC power lines124. The UPS120can also include a DC/DC converter on the DC side of the AC/DC converter, as described below.

In normal operation, the bidirectional AC/DC converter can operate in a first mode in which the AC/DC converter converts the AC power on the AC power lines122provided by the AC power source160to DC power and outputs the DC power onto the DC power lines124. This DC power can charge the backup batteries150and power the DC load(s)140. A controller of the UPS120can put the AC/DC converter into the first mode when the AC power source160is available and does not have any faults.

When the AC power source160is not available or has a fault, e.g., a power failure, the controller can put the bidirectional AC/DC converter in a second mode in which the bidirectional AC/DC converter converts the DC power on the DC power lines124to AC power and outputs the AC power onto the AC power lines122. In this mode, the backup batteries150provides the DC power on the DC power lines124. The backup batteries150also provides power to the DC power load(s)140via the DC power lines124when the bidirectional AC/DC converter is in the second mode of operation. The AC power output by the UPS120onto the AC power lines122powers the AC load(s)130.

In this way, only AC power has to be routed to the rack105and the rack105does not need both an AC UPS and a DC UPS to power the AC load(s)130and the DC load(s)140. Instead, the UPS120and batteries150can power both loads when the AC power source160is not available or is faulty.

The rack105also includes a power distribution unit (PDU)110. The PDU110can distribute power to the AC load(s)130and/or DC load(s)140. For example, the AC or DC output of the UPS120can be connected to the PDU110. That is, rather than connecting the output directly to the loads, the output can be connected to the PDU110, which is connected to the loads. The PDU110can include multiple outlets to which the AC load(s)130or DC load(s) can connect. In some implementations, the rack105can include a respective PDU110for each type of load, e.g., a PDU for the AC load(s)130and a PDU for the DC load(s). In this example, the AC output of the UPS120can be connected to the input of the AC PDU and the outlets of the AC PDU can be connected to the AC load(s)130. Similarly, the DC output of the UPS120can be connected to the input of DC PDU and the outputs of the DC PDU can be connected to the DC load(s)140.

FIG. 2is a block diagram of another environment200in which an example UPS system230provides power to DC and AC loads in the event of a power failure. The UPS system230includes a UPS231and a backup battery250. The backup battery250can include multiple batteries.

The UPS231includes AC terminals236A and236B connected to an AC power source210by way of AC power lines212A and212B (e.g., cables, insulated wires, or other conductors) and a bypass switch211. The AC power source210can be, for example, a 120 VAC or 220 VAC power source. One or more AC load(s)220are also connected to the AC power lines212A and212B. During normal operation when the AC power source210, the bypass switch211is closed allowing the AC power source210to provide input AC power to the UPS231and to the AC load(s)220. As described in more detail below, a controller234can operate the bypass switch211based on whether the AC power source210is available.

In general, an AC load220is a load that receives AC power as input. In this example, the AC load220includes an AC/DC converter221that converts the AC power input to DC power for one or more DC load(s) of the AC load220. For example, some off the shelf computing equipment is adapted in this way to plug into AC outlets, but to operate DC-powered computing equipment. The AC load222also includes a DC/DC converter222that can adjust the voltage level of the DC power output by the AC/DC converter221. For example, the DC/DC converter222can step down the voltage for the DC load(s)223.

The UPS231includes a bidirectional AC/DC converter232and a bidirectional DC/DC converter233. The AC side of the AC/DC converter232is connected to the AC terminals236A and236B. In a first mode, the bidirectional AC/DC converter232converts AC power received at the AC terminals236A and236B to DC power that is output to the DC/DC converter233on the DC side of the AC/DC converter232. In a second mode, the bidirectional AC/DC converter232converts DC power output by the bidirectional DC/DC converter233to AC power provided to the AC terminals236A and236B. These two modes are described in more detail below.

In some implementations, the bypass switch211is part of the UPS231, e.g., in the same housing of package as the UPS231. In this example, the UPS230can include AC input terminals that are connected to the AC power source210. The bypass switch211can be connected between one of the AC input terminals and the AC/DC converter232. The UPS230can also include AC output terminals. The AC output terminals can be connected to the AC load(s)230. For example, the AC output terminals can be connected as an input to a PDU and each AC load230can be connected to an output of the PDU.

In a first mode, the DC/DC converter233can step down the voltage output by the bidirectional AC/DC converter232and output the lower voltage DC power at DC terminals237A and237B. In a second mode, the bidirectional DC/DC converter233can step up voltage received at the DC terminals237A and237B for input to the bidirectional AC/DC converter232. These two modes are described in more detail below.

The DC terminals237A and237B are connected to DC power lines240A and240B. The DC power lines240A and240B are also connected to the backup battery250and one or more DC loads260. The DC load(s)260can operate on DC power that has the same voltage level as the backup battery's rated voltage. In this way, the backup battery250can power the DC load(s)260when the AC power source210is not available. For example, the backup battery250can be rated for 48 VDC and the DC load(s)260can operate on 48 VDC power.

The controller234can monitor the AC power source210and detect whenever there is a power failure. The controller234can operate the bypass switch211, the bidirectional AC/DC converter232, and the bidirectional DC/DC converter233based on the status of the AC power source210, e.g., whether the AC power source is available or there is a power failure.

When the AC power source210is available, the controller234closes the bypass switch211and operates both the bidirectional AC/DC converter232and the bidirectional DC/DC converter233in their respective first modes. With the AC power source210available and the bypass switch211closed, the AC power source210provides AC power to the AC terminals236A and236B and the AC load(s)220. This powers the AC load(s)220. In addition, the UPS231converts the AC power to DC power for charging the backup battery250and powering the DC load(s)260.

In the first mode, the bidirectional AC/DC converter232converts the AC power received at the AC power terminals236A and236B to DC power for the bidirectional DC/DC converter. That is, the bidirectional AC/DC converter232is configured to act as a rectifier in the first mode. In the first mode, the bidirectional DC/DC converter233steps down the DC power output by the bidirectional AC/DC converter232to a lower voltage for the DC terminals237A and237B. This DC power charges the backup battery250and powers the DC load(s)260by way of the DC power lines240A and240B. In a particular implementation, the AC input voltage to the AC power terminals can be between 85-265 Vrms. In this example, the DV output voltage of the AC/DC converter232can be about 400 VDC and the DC output voltage of the DC/DC converter233(e.g., at the DC terminals237A and237B) can be about 54 VDC.

When the controller234detects a power failure of the AC power source210, the controller234opens the bypass switch211to isolate the UPS system230, the AC load(s)220, and the DC load(s)260from the AC power source210. The controller234also switches the bidirectional AC/DC converter232and the bidirectional DC/DC converter233to their respective second modes in response to the power failure.

During a power failure, the backup battery250becomes the power source for the UPS231and the DC load(s)260. The backup battery250provides DC power to the UPS231and the DC load(s)260over the power lines240A and240B and to the DC terminals237A and237B. Thus, the DC terminals237A and237B can be DC input terminals and DC output terminals.

In the second mode, the bidirectional DC/DC converter233steps up the DC voltage received at the DC terminals237A and237B provided by the backup battery250. In the second mode, the bidirectional AC/DC converter232converts the stepped up DC power output by the bidirectional DC/DC converter233to AC power and outputs the AC power onto the AC terminals236A and236B. That is, the bidirectional AC/DC converter232is configured to act as an inverter in the second mode. This AC power output by the bidirectional AC/DC converter powers the AC load(s)220during the power failure. Thus, during the power failure, the UPS system230provides power to both the AC load(s)220and the DC load(s)260.

Various types of single phase bidirectional AC/DC converters can be used in the UPS231. In general, the AC/DC converter232can include an arrangement of switches and energy storing components (e.g., capacitors and inductors). The switches can be operated differently when converting AC power to DC power than when converting DC power to AC power. The controller234can control the switches, e.g., by turning the switches on and off depending on the mode of the AC/DC converter232.

A circuit diagram of an example bidirectional AC/DC converter232is illustrated inFIG. 2. In general, when the bidirectional AC/DC converter232is in the first mode as a rectifier, the controller234operates switches Q1-Q8to perform zero voltage switching (ZVS). The controller234also operates switches Q9-Q12to perform zero current switching (ZCS). The controller234operates the switches Q1-Q12to control an LLC270that includes two inductors and a capacitor using closed-loop control to regulate the voltage level of the DC output power. For example, the controller234can receive voltage measurements of the DC output power, e.g., at the DC terminals237A and237B, and adjust the switching frequency of the switches Q1-Q12to adjust the voltage level.

When the bidirectional AC/DC converter232is in the second mode as an inverter, the controller operates the switches Q1-Q8to perform ZVS and the switches Q9-Q12to perform ZCS. The controller234also operates the LLC270as LC and DC transformers, and the LC is operating at resonant frequency. The controller234can adjust the modulation index of the totem pole stage to regulate the voltage level of the AC output power. For example, the controller234can receive voltage measurements of the AC output and adjust the modulation index of the totem pole stage to bring the voltage level of the AC output to the appropriate voltage level.

In some implementations, the bidirectional DC/DC converter233is optional and can be excluded. For example, the bidirectional DC/DC converter233can be excluded in implementations in which the bidirectional AC/DC converter232converts AC power to DC power having the same voltage level as the rated voltage of the backup battery250and the voltage level of the DC. This can reduce the cost of the UPS230.

The UPS system230also includes optional capacitors235and244. The capacitor235can be used to condition the DC power between the two converters232and233. Similarly, the capacitor244can be used to condition the DC power between the bidirectional DC/DC converter233and the backup battery250and DC load(s)260. For example, the capacitors235and244can be used to smooth the voltage levels at these points.

The UPS system230can be implemented as a packaged solution that includes the UPS231, the bypass switch211, and optionally the backup battery250. In this way, the UPS system230can be used to provide power to AC and DC loads in various applications, e.g., in electric vehicles, mission critical industrial applications, etc.

FIG. 3is a flow diagram that illustrates an example process300for providing power to DC and AC loads in the event of a power failure. The process300can be performed by a UPS, e.g., the UPS120ofFIG. 1or the UPS231ofFIG. 2.

An AC power source is monitored (302). A controller can monitor the AC power source for the availability of input power and/or for a power failure. For example, the controller can monitor the AC power source for a specified set of power failures, such as loss of input power for the loads, power sags, power surges, under voltage conditions, over voltage conditions, noise on the power line, frequency variation, switching transients, and/or harmonics.

A determination is made whether the AC power source is available (304). The power source may be considered available when power from the power source is detected and none of the power failures are detected. The controller can continuously monitor the AC power source and make this determination continuously based on the monitoring.

If the AC power source is available, a bidirectional AC/DC converter of the UPS is operated in a first mode of operation (306). For example, the controller can operate the bidirectional AC/DC converter in the first mode of operation. In the first mode, the AC/DC converter converts AC power from the AC power source to DC power. The output DC power can recharge a backup battery and power one or more DC loads. In addition, the AC power source and the AC side of the AC/DC converter can be connected to one or more AC loads. In the first mode, the AC power source powers the AC load(s).

If the AC power source is not available, the bidirectional AC/DC converter of the UPS is operated in a second mode of operation (308). For example, the controller can operate the bidirectional AC/DC converter in the second mode of operation. In the second mode, the bidirectional AC/DC converter converts DC power from the backup battery to AC power. For example, when the AC power source is no longer available, e.g., a power failure occurs, a bypass switch between the AC power source and the bidirectional AC/DC converter can be opened to isolate the UPS from the AC power sources. The backup battery can then provide DC power to the DC side of the AC/DC converter and to the DC load(s).

The bidirectional AC/DC converter can convert the DC power to AC power. The bidirectional AC/DC converter can output the AC power to the AC load(s) to power the AC load(s). In this way, the UPS provides power to both AC and DC loads when the AC power source is not available.