Patent Description:
Electrical appliances (e.g., office or home equipment, measuring instruments, medical devices, datacenter equipment such as routers and servers, etc.) may be configured to receive and operate on AC or DC power from an AC or DC source. Such electrical appliances are commonly coupled to an AC or DC power outlet that provides AC or DC power to the appliance from an AC or DC source. The power outlet may be one of a plurality of power outlets of a power distribution unit (e.g., a power strip). The AC or DC power received by an appliance from a power outlet may be provided directly to the appliance from the outlet or may first be conditioned via an Uninterruptible Power Supply (UPS) coupled between the power outlet and the appliance.

The use of a power device, such as a UPS, to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems, datacenter equipment, and other data processing systems, is known. In general, a UPS includes, or is connected to, both a primary source of power and an alternate source of power where the alternate source of power can be employed to supply power to the electrical load when the primary source is not available (i.e., in a backup mode of operation). Often, the primary source of power is an AC power source such as power supplied from an electric utility. The alternate source of power generally includes one or more batteries supplying DC power which is converted by the UPS into AC power and provided to the electrical load during the backup mode of operation. The batteries are generally recharged by a battery charger coupled to the UPS that receives power provided to the UPS by the primary source of power.

In particular, the invention is directed, in a first aspect corresponding to independent claim <NUM>, to a Uninterruptible Power Supply (UPS) and in a further aspect corresponding to independent claim <NUM>, to a method for operating an UPS. One aspect in accord with the present invention is directed to an Uninterruptible Power Supply (UPS) comprising an input configured to be coupled to an AC source and to receive input AC power from the AC source, a DC bus configured to be coupled to a DC source and to receive backup DC power from the DC source, a first output configured to be coupled to at least one AC load and to provide output AC power having an output AC voltage to the at least one AC load derived from at least one of the input AC power and the backup DC power, a second output configured to be coupled to at least one DC load and to provide output DC power having an output DC voltage to the at least one DC load derived from at least one of the input AC power and the backup DC power, a first bidirectional inverter coupled between the DC bus and a first transformer, the first transformer coupled to the input and configured to provide isolation between the input and the DC source, a second bidirectional inverter coupled between the DC bus and a second transformer, the second transformer coupled to the first output and configured to provide isolation between the first output and the second output, and a controller configured to operate the second inverter to maintain the output AC voltage above a first threshold value and to operate the first inverter to maintain the output DC voltage above a second threshold.

A primary winding of the first transformer is coupled between the input and the first output, and a secondary winding of the first transformer is coupled to the first inverter. In one embodiment, the controller is further configured to monitor a voltage level of the DC bus and, based on the voltage level of the DC bus, to operate the first inverter to adjust the input AC power by regulating current in the secondary winding of the first transformer.

According to another embodiment, the controller is further configured to determine whether the voltage level of the DC bus is at a desired float level, and in response to a determination that the voltage level of the DC bus is less than the desired float level, to operate the first inverter to increase the input AC power, convert at least a portion of the increased input AC power, from the first transformer, into DC power, and provide the converted DC power from the first inverter to the DC bus. In one embodiment, the controller is further configured to operate the second inverter to convert at least a portion of the increased input AC power, from the second transformer, into DC power and provide the converted DC power from the second inverter to the DC bus. In another embodiment, the controller is further configured, in response to a determination that the voltage level of the DC bus is greater than the desired float level, to operate the first inverter to decrease the input AC power, convert DC power from the DC bus into AC power, and provide the converted AC power from the first inverter to the input via the first transformer.

A primary winding of the second transformer is coupled between the first output and ground, and a secondary winding of the second transformer is coupled to the second inverter. In one embodiment, the controller is further configured to monitor the output AC voltage and, in response to a determination that the output AC voltage is less than the first threshold value, to operate the second inverter to convert DC power from the DC bus into AC power and provide the converted AC power from the second inverter to the first output via the second transformer. The controller is further configured, in response to a determination that the output AC voltage is greater than the first threshold value, to operate the second inverter to convert a portion of the output AC power, from the second transformer, into DC power and provide the converted DC power from the second inverter to the DC bus.

Another aspect in accord with the present invention is directed to a method for operating a UPS having an input to receive input AC power, a DC bus configured to receive backup DC power, a first output configured to be coupled to at least one AC load and to provide output AC power having an output AC voltage to the at least one AC load derived from at least one of the input AC power and the backup DC power, a second output configured to be coupled to at least one DC load and to provide output DC power having an output DC voltage to the at least one DC load derived from at least one of the input AC power and the backup DC power, wherein the method comprises monitoring, with a controller, the output DC voltage provided to the at least one DC load, monitoring, with the controller, the output AC voltage provided to the at least one AC load, operating a first bidirectional inverter coupled between the DC bus and the input to maintain the output DC voltage provided to the at least one DC load above a first threshold, operating a second bidirectional inverter coupled between the DC bus and the first output to maintain the output AC voltage provided to the at least one AC load above a second threshold, and providing isolation between the first output and the second output.

The first inverter is coupled to the input via a first transformer, the first transformer having a primary winding coupled between the input and the first output and a secondary winding coupled to the first inverter. According to one embodiment, monitoring the output DC voltage includes monitoring a DC voltage level of the DC bus, and operating the first inverter includes operating, based on the DC voltage level of the DC bus, the first inverter to adjust the input AC power by regulating current in the secondary winding of the first transformer.

According to another embodiment, operating the first inverter to adjust the input AC power includes determining whether the DC voltage level of the DC bus is less than a desired float level, in response to a determination that the DC voltage level of the DC bus is less than the desired float level, operating the first inverter to increase the input AC power, converting at least a portion of the increased input AC power, from the first transformer, into DC power, and providing the converted DC power from the first inverter to the DC bus.

According to one embodiment, the method further comprises operating the second inverter to convert at least a portion of the increased input AC power, from the second transformer, into DC power, and providing the converted DC power from the second inverter to the DC bus. In one embodiment, operating the first inverter to adjust the input AC power further includes, in response to a determination that the DC voltage level of the DC bus is greater than the desired float level, operating the first inverter to decrease the input AC power, converting DC power from the DC bus into AC power, and providing the converted AC power from the first inverter to the input via the first transformer.

The second inverter is coupled to the first output via a second transformer, the second transformer having a primary winding coupled between the first output and ground and a secondary winding coupled to the second inverter. According to another embodiment, operating the second inverter includes, in response to a determination that the output AC voltage is less than the second threshold, operating the second inverter to convert DC power from the DC bus into AC power, and providing the converted AC power from the second inverter to the first output via the second transformer. In one embodiment, operating the second inverter further includes, in response to a determination that the output AC voltage is greater than the second threshold, operating the second inverter to convert a portion of the output AC power, from the second transformer, into DC power, and providing the converted DC power from the second inverter to the DC bus.

In the drawings, each identical or nearly identical component that is illustrated in various FIGs. is represented by a like numeral. In the drawings:.

The use of "including," "comprising," or "having," "containing", "involving", and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

As discussed above, electrical appliances may be configured to receive and operate on AC or DC power from an AC or DC source. Some systems or installations may include both AC powered and DC powered appliances. For example, datacenters typically include mixed-source electrical appliances, with some appliances operating on AC power and some appliances operating on DC power. This may prove problematic where connection of both types of appliances (AC and DC) to a UPS system is desired.

A standard approach to accommodate both AC and DC powered appliances within a datacenter is to include separate UPS systems with respective AC and DC outputs within the datacenter. However, this may lead to a large, complex and relatively expensive system to install and maintain. Additionally, the split between the number of AC powered loads and DC power loads within the datacenter may change over time, resulting in insufficient UPS support and/or stranded capacity within the datacenter. For example, if a datacenter with separate AC and DC UPS systems is initially designed to accommodate a fixed number of AC and DC powered loads, the future development or conversion of additional DC power loads within the datacenter (i.e., a higher deployment of DC loads in the datacenter) may result in the datacenter not having enough DC UPS systems to accommodate each DC powered load and the AC UPS systems having stranded capacity (i.e., unused capacity).

Accordingly, embodiments described herein provide a UPS with both AC and DC outputs that is capable of providing power to both AC and DC powered loads. By providing a single UPS with both AC and DC outputs, the complexity of UPS systems within a datacenter may be reduced and the single UPS may be adapted to meet different AC and DC load requirements of the datacenter. Additionally, according to some embodiments, the UPS described herein may be relatively efficient, able to provide isolation between AC and DC loads, and provide Power Factor Correction (PFC) functionality for both AC and DC loads.

<FIG> shows a UPS <NUM> according to aspects described herein. The UPS <NUM> is based on a delta conversion topology. For example, according to one embodiment, the UPS <NUM> utilizes some aspects of a delta conversion topology as implemented in the Symmetra® MW model of UPS's sold by Schneider Electric IT Corporation of West Kingston, Rhode Island; however, in other embodiments, other types of delta conversion topologies may be utilized. The UPS <NUM> includes an AC mains input <NUM>, a mains switch <NUM>, a first transformer <NUM>, a second transformer <NUM>, and AC output <NUM>, a delta inverter <NUM>, a main inverter <NUM>, a DC bus <NUM>, a first battery <NUM>, a second battery <NUM>, a DC output <NUM>, and a controller <NUM>.

The AC mains input <NUM> is coupled to a first end of a primary winding <NUM> of the first transformer <NUM> via the mains switch <NUM>. The other end of the primary winding <NUM> is coupled to the AC output <NUM>. The secondary winding <NUM> of the primary transformer <NUM> is coupled to an AC interface <NUM> of the delta inverter <NUM>. A primary winding <NUM> of the second transformer <NUM> is coupled between the AC output <NUM> and ground <NUM>. A secondary winding <NUM> of the second transformer is coupled to an AC interface <NUM> of the main inverter <NUM>. A DC interface <NUM> of the delta inverter <NUM> and a DC interface <NUM> of the main inverter <NUM> are both coupled to the DC output <NUM> via the DC bus <NUM>. The first battery <NUM> and the second battery <NUM> are coupled in series between the DC bus <NUM> and ground <NUM>. The controller <NUM> is coupled to the DC bus <NUM>, the delta inverter <NUM> and the main inverter <NUM>. The AC output <NUM> is configured to be coupled to external AC loads. The DC output <NUM> is configured to be coupled to external DC loads.

The delta inverter <NUM> and the main inverter <NUM> are bidirectional devices (i.e., each is capable of converting power from AC to DC and from DC to AC). In an online mode of operation, once the mains switch <NUM> is closed, mains input AC power (e.g., from an AC utility source coupled to the AC mains input <NUM>) is provided to the primary winding <NUM> of the first transformer. DC power from the batteries <NUM>, <NUM> is provided to the DC interface <NUM> of the delta inverter <NUM>. The delta inverter <NUM> converts the DC power from the batteries <NUM>, <NUM> into AC power and provides the AC power to the secondary winding <NUM> of the first transformer <NUM>.

The delta inverter <NUM> is operated by the controller <NUM> to act as a current source and regulate the current in the secondary winding <NUM> of the first transformer <NUM>. By regulating the current in the secondary winding <NUM> of the first transformer <NUM>, the delta inverter <NUM> also controls the current through the primary winding <NUM> of the first transformer <NUM> (i.e., the input current of the UPS <NUM>). The current through the primary winding <NUM> of the first transformer <NUM> (regulated by the delta inverter <NUM>) is provided to external AC loads coupled to the AC output <NUM>.

The controller <NUM> can be configured to operate the delta inverter <NUM> to provide power factor correction. For example the controller <NUM> is configured to operate the delta inverter <NUM> to draw only sinusoidal input current (from the AC utility) that is substantially in phase with AC voltage provided to the AC input <NUM> by the AC utility. This may ensure that power is drawn from the AC utility with a unity power factor.

Operation of the UPS <NUM> is discussed in greater detail below with regard to <FIG> and <FIG>. <FIG> is a flow chart <NUM> of a process for operating the main inverter <NUM> according to at least one embodiment described herein. The controller <NUM> operates the main inverter <NUM> to maintain AC output voltage of the UPS <NUM> at a level sufficient to power AC loads coupled to the AC output <NUM>.

In the online mode of operation, at block <NUM>, AC power from the primary winding <NUM> of the first transformer <NUM> is provided to the AC output <NUM>. At block <NUM>, as AC power from the primary winding <NUM> of the first transformer <NUM> is provided to the AC output <NUM>, the controller <NUM>, via the main inverter <NUM> and the second transformer <NUM>, monitors the AC voltage of the AC power at the AC output <NUM>. Based on the monitored AC voltage at the AC output <NUM>, the controller <NUM> operates the main inverter <NUM> to act as a voltage source and maintain a relatively constant AC voltage at the AC output <NUM>. For example, at block <NUM>, the controller <NUM> determines if the AC voltage at the AC output <NUM> is at least at an AC output voltage threshold level (i.e., a level sufficient to adequately support AC loads coupled to the AC output <NUM>).

At block <NUM>, if the controller <NUM> determines that the AC voltage at the AC output <NUM> is low (i.e., is below the AC output voltage threshold level), the controller <NUM> operates the main inverter <NUM> to convert DC power from the DC bus <NUM>, received at the DC interface <NUM>, into AC power and provide the converted AC power, via the AC interface <NUM> and the second transformer <NUM>, to the AC output <NUM> to increase the AC voltage at the AC output <NUM>.

At block <NUM>, in response to a determination by the controller <NUM> that the AC voltage at the AC output <NUM> is at least at the AC output voltage threshold level, another determination is made by the controller <NUM> whether the AC voltage at the AC output <NUM> is greater than the AC output voltage threshold level. In response to a determination by the controller <NUM> that the AC voltage at the AC output <NUM> is at the AC output voltage threshold level, at block <NUM> the controller <NUM> continues to monitor the AC voltage at the AC output <NUM>.

At block <NUM>, in response to a determination by the controller <NUM> that the AC voltage at the AC output <NUM> is high (i.e., greater than the AC output voltage threshold level), the controller <NUM> operates the main inverter <NUM> to convert AC power from the AC output <NUM>, received at the AC interface <NUM> via the second transformer <NUM>, into DC power (consequently decreasing the AC voltage at the AC output <NUM>) and provide the converted DC power, via the DC interface <NUM>, to the DC bus <NUM>. The DC power on the DC bus <NUM> charges or maintains the batteries <NUM>, <NUM> and/or is provided to DC loads coupled to the DC output <NUM>. At block <NUM> the controller <NUM> continues to monitor the AC voltage at the AC output <NUM>.

<FIG> is a flow chart <NUM> of a process for operating the delta inverter <NUM> according to at least one embodiment described herein. The controller <NUM> operates the delta inverter <NUM> to maintain DC output voltage of the UPS <NUM> at a level sufficient to power DC loads coupled to the DC output <NUM>.

In the online mode of operation, at block <NUM>, the UPS <NUM> provides AC power to AC loads coupled to the AC output <NUM> and DC power to DC loads coupled to the DC output <NUM>. As AC power is provided to the AC loads and DC power is provided to the DC loads, the controller <NUM> is configured to control the delta inverter <NUM> to regulate the input current of the UPS <NUM> (by regulating the current in the secondary winding <NUM> of the first transformer as discussed above) so that there is sufficient power available from the UPS <NUM> to power both the AC loads coupled to the AC output <NUM> and the DC loads coupled to the DC output <NUM>.

According to one embodiment, a regulation loop including the DC bus <NUM>, the controller <NUM>, and the delta inverter <NUM> is utilized to maintain a desired float voltage on the DC bus <NUM>. The controller <NUM> monitors the DC voltage on the DC bus, and based on the sensed DC voltage, regulates the amplitude of the input current of the UPS <NUM> to ensure that the UPS <NUM> is drawing enough power from AC mains to cover the sum of power drawn by the UPS <NUM> (including power drawn by the AC loads coupled to the AC output <NUM>, power drawn by the DC loads coupled to the DC output <NUM>, power required to recharge or maintain the batteries <NUM>, <NUM>, and power to cover any UPS losses).

For example, at block <NUM>, the controller <NUM> monitors the level of the DC voltage on the DC bus <NUM>. At block <NUM>, the controller <NUM> determines if the DC bus voltage is at least at a desired float voltage level (i.e., a threshold level sufficient to power DC loads coupled to the DC output <NUM> and charge or maintain the batteries <NUM>, <NUM>). At block <NUM>, in response to a determination by the controller <NUM> that the DC bus voltage is low (i.e., below the desired float voltage level) the controller <NUM> recognizes that insufficient AC power is being drawn from AC mains to adequately cover the sum of power drawn by the AC loads, DC loads and the batteries <NUM>, <NUM>.

The presence of a low DC voltage on the DC bus may result from multiple different conditions within the UPS <NUM>. For example, in one embodiment, where the AC power provided to the AC output <NUM> (being regulated by the main inverter <NUM>) is adequate to power the AC loads, excess DC power provided by the main inverter <NUM> to the DC bus <NUM> may be inadequate to power the DC loads coupled to the DC output <NUM> and to charge or maintain the batteries <NUM>, <NUM>, resulting in the low voltage on the DC bus. In another embodiment, where AC power provided to the AC output <NUM> via the primary winding <NUM> of the first transformer is inadequate, additional power may be pulled from the DC bus <NUM> by the main inverter <NUM> and provided to the AC output <NUM>, resulting in the reduced voltage on the DC bus. In another embodiment, the AC mains power being drawn by the UPS <NUM> may be insufficient to meet the total power needs of the UPS <NUM>, resulting in the reduced voltage on the DC bus.

Upon sensing a low DC voltage level on the DC bus <NUM>, the controller <NUM> operates the delta inverter <NUM> to regulate the amplitude of the input current of the UPS <NUM> to resolve the power deficiency within the UPS <NUM> indicated by the low DC voltage level on the DC bus <NUM>. For example, at block <NUM>, in response to sensing a low DC voltage level on the DC bus <NUM>, the controller <NUM> operates the delta inverter <NUM> to increase the input current of the UPS <NUM>. According to one embodiment, at block <NUM>, at least a portion of the additional AC power generated by the increase in input current is received by the AC interface <NUM> of the delta inverter <NUM> via the first transformer <NUM>, converted by the delta inverter <NUM> into DC power and provided, via the DC interface <NUM>, to the DC bus <NUM> to increase the DC voltage level (and consequently DC power available) on the DC bus. According to one embodiment, at block <NUM>, at least a portion of the additional AC power generated by the increase in input current may be provided to the AC output <NUM> to increase the AC power at the AC output <NUM>. The increased AC power at the AC output <NUM> is regulated by the main inverter <NUM> (as discussed above with regard to <FIG>) and may be provided to AC loads coupled to the AC output <NUM> and/or converted to DC power and provided to the DC bus <NUM> if excess power is available at the AC output <NUM>.

At block <NUM>, the controller <NUM> continues to monitor the DC bus voltage level. According to one embodiment, once the controller <NUM> senses that the DC voltage level on the DC bus <NUM> is no longer low (i.e., at least at the desired float voltage level), the controller <NUM> operates the delta inverter <NUM> to stop pulling AC power from the input <NUM>, via the first transformer <NUM> (and converting it into DC power), and to regulate the input current of the UPS so that the AC power provided to the primary winding <NUM> of the first transformer <NUM> by AC mains is adequate to cover the power needs of the UPS <NUM>.

At block <NUM>, in response to a determination by the controller <NUM> that the DC bus voltage is at least at the desired float voltage level, another determination is made by the controller <NUM> whether the DC bus voltage is greater than the desired float voltage level. In response to a determination by the controller <NUM> that the DC bus voltage is at the desired float voltage level, at block <NUM> the controller <NUM> continues to monitor the DC voltage on the DC bus <NUM>.

At block <NUM>, in response to a determination by the controller <NUM> that the DC bus voltage is high (i.e., greater than the desired float voltage level), the controller <NUM> recognizes that too much AC power is being drawn from AC mains. The presence of a high DC voltage on the DC bus (indicating an overdraw of input current by the UPS <NUM>) may result from multiple different conditions within the UPS <NUM>.

For example, in one embodiment, where the AC power provided to the AC output <NUM> (being regulated by the main inverter <NUM>) is adequate to power the AC loads currently coupled to the AC output <NUM>, the excess DC power provided by the main inverter <NUM> to the DC bus <NUM> and/or the DC power provided by the delta inverter <NUM> to the DC bus <NUM> may be more than is required to power the DC loads currently coupled to the DC output <NUM> and to charge or maintain the batteries <NUM>, <NUM>, resulting in the high voltage on the DC bus.

Upon sensing a high DC voltage level on the DC bus <NUM>, the controller <NUM> operates the delta inverter <NUM> to regulate the amplitude of the input current of the UPS <NUM> to resolve the excess power being drawn by the UPS <NUM>, indicated by the high DC voltage level on the DC bus <NUM>. For example, according to one embodiment, at block <NUM>, in response to sensing a high DC voltage level on the DC bus <NUM>, the controller <NUM> operates the delta inverter <NUM> to decrease the input current of the UPS <NUM>. At block <NUM>, the controller <NUM> also operates the delta inverter <NUM> to convert DC power received from the DC bus <NUM> via the DC interface <NUM> into AC power to reduce the DC voltage level on the DC bus <NUM>, and provide the converted AC power to the input <NUM>, via the first transformer <NUM>. The controller <NUM> operates the delta inverter <NUM> to regulate the input current of the UPS and to provide AC power to the first transformer <NUM> such that the sum of AC power received at the AC input <NUM> from AC mains and the delta inverter <NUM> is adequate to cover the power needs of the UPS <NUM> but also so that the DC voltage level on the DC bus <NUM> is reduced.

At block <NUM>, the controller <NUM> continues to monitor the DC bus voltage level. According to one embodiment, once the controller <NUM> senses that the DC voltage level on the DC bus <NUM> is no longer high, the controller <NUM> operates the delta inverter <NUM> to stop pulling DC power from the DC bus (and converting it into AC power) and to regulate the input current of the UPS so that the AC power provided to the primary winding <NUM> of the first transformer <NUM> by AC mains is adequate to cover the power needs of the UPS <NUM>.

In a backup mode of operation of the UPS <NUM> (e.g., where the AC mains coupled to the AC input <NUM> fails), DC power from the batteries <NUM>, <NUM> is provided to the DC loads coupled to the DC output <NUM> via the DC bus <NUM>. The DC power on the DC bus <NUM> is also received by the main inverter <NUM> via the DC interface <NUM>, converted to AC power, and provided to the AC loads coupled to the AC output <NUM> via the second transformer <NUM>.

By maintaining a desired float voltage on the DC bus <NUM> in the online mode of operation, the control loop of the controller <NUM>, DC bus <NUM> and delta inverter <NUM> is able to ensure that adequate power is available to be provided by the single UPS <NUM> to both AC loads and DC loads in a datacenter. The UPS <NUM> is also flexible in that it may be adapted to provide AC power to any number of AC loads coupled to the AC output and DC power to any number of DC loads coupled to the DC output. The UPS <NUM> supports the AC loads by controlling the main inverter <NUM> to maintain a constant AC voltage at the AC output <NUM> capable of supporting the AC loads currently coupled to the AC output <NUM>. The UPS <NUM> supports the DC loads by maintaining a desired float voltage on the DC bus which is capable of supporting the DC loads currently coupled to the DC output <NUM>.

The first <NUM> and second transformers <NUM> provide galvanic isolation between the DC output <NUM> and the AC output <NUM> (and also between the AC input <NUM> and the batteries <NUM>, <NUM>). The galvanic isolation provided by the transformers <NUM>, <NUM> may enhance the safety of the UPS <NUM>. For example, absent the galvanic isolation, when DC power is being provided to DC loads coupled to the DC output <NUM> and AC power is being provided to AC loads coupled to the AC output <NUM>, safety critical arc flash scenarios may arise if any ground faults in the DC bus <NUM>, DC output <NUM>, or DC loads occur. The galvanic isolation provided by the transformers <NUM>, <NUM> may prevent such arc flashes.

According to one embodiment, the isolation between the AC output <NUM> and the DC output <NUM> provided by the transformers <NUM>, <NUM> may allow for wide flexibility in the configuration of the AC voltage at the AC output <NUM> and the DC voltage at the DC output <NUM>. For example, according to one embodiment, the AC voltage at the AC output <NUM> (regulated by the main inverter <NUM>) may be defined as any AC voltage (e.g., 3x480V AC). Due to the isolation between the AC output <NUM> and the DC output provided by the transformers <NUM>, <NUM>, the DC voltage on the DC output <NUM> is fully floating and is isolated from the AC voltage of the AC output. Accordingly, the floating DC voltage on the DC bus <NUM> may be defined as any desired DC voltage depending on the requirements of the DC loads coupled to the DC output <NUM> and is not restricted by the AC voltage at the AC output <NUM>.

For example, according to one embodiment and as illustrated in <FIG>, where the batteries <NUM>, <NUM> are coupled in series (with the negative terminal <NUM> of the battery <NUM> coupled to ground <NUM> and the positive terminal <NUM> of the battery <NUM> coupled to the DC bus <NUM>) to provide a positive DC voltage to the DC bus <NUM>, the floating DC voltage may be defined as a positive floating DC voltage (e.g., +380V DC). According to another embodiment, where the batteries <NUM>, <NUM> are coupled in series (with the positive terminal <NUM> of the battery <NUM> coupled to ground <NUM> and the negative terminal <NUM> of the battery <NUM> coupled to the DC bus <NUM>) to provide a negative DC voltage to the DC bus <NUM>, the floating DC voltage may be defined as a negative floating DC voltage (e.g., -380V DC). According to another embodiment, where the DC bus <NUM> is coupled at a point <NUM> between the batteries <NUM>, <NUM> (with the negative terminal <NUM> of the battery <NUM> being coupled to the DC bus <NUM> and the positive terminal <NUM> of the battery <NUM> being coupled to the DC bus <NUM>), the floating DC voltage on the DC bus <NUM> may be defined as any other DC value generated by the sum of the negative voltage from the battery <NUM> and the positive voltage from the battery <NUM>.

By isolating the AC output <NUM> from the DC output <NUM>, the UPS <NUM> is able to generate any desired floating DC voltage on the DC bus <NUM> to be provided to DC loads coupled to the DC output <NUM>. This may allow the UPS <NUM> to be flexible and adapt to different DC voltage levels required by DC loads coupled to the UPS <NUM>.

As described above, the UPS includes two batteries; however, in other embodiments, the UPS may include any number of batteries.

As also described above, the UPS includes a single controller to operate the UPS; however, in other embodiments, more than one controller may be included within the UPS to control the operation of the UPS.

Claim 1:
An Uninterruptible Power Supply, UPS, (<NUM>) comprising:
an input (<NUM>) configured to be coupled to an AC source and to receive input AC power from the AC source;
a DC bus (<NUM>) configured to be coupled to a DC source (<NUM>, <NUM>) and to receive backup DC power from the DC source;
a first output (<NUM>) configured to be coupled to at least one AC load and to provide output AC power having an output AC voltage to the at least one AC load derived from at least one of the input AC power and the backup DC power;
a second output (<NUM>) configured to be coupled to at least one DC load and to provide via the DC bus output DC power having an output DC voltage to the at least one DC load derived from at least one of the input AC power and the backup DC power;
a first bidirectional inverter (<NUM>) coupled between the DC bus and a first transformer (<NUM>), the first transformer coupled to the input and configured to provide galvanic isolation between the input and the DC source;
a second bidirectional inverter (<NUM>) coupled between the DC bus and a second transformer (<NUM>), the second transformer coupled to the first output and configured to provide galvanic isolation between the first output and the second output; and
a controller (<NUM>) configured to operate the second bidirectional inverter to maintain the output AC voltage above a first threshold value and to operate the first bidirectional inverter to maintain the output DC voltage above a second threshold;
wherein a primary winding (<NUM>) of the first transformer is coupled between the input and the first output, and wherein a secondary winding (<NUM>) of the first transformer is coupled to an AC interface (<NUM>) of the first bidirectional inverter; and
a primary winding (<NUM>) of the second transformer is coupled between the first output and ground, and wherein a secondary winding (<NUM>) of the second transformer is coupled to an AC interface (<NUM>) of the second bidirectional inverter.