Patent Description:
Power devices, such as uninterruptible power supplies (UPSs), may be used to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems and other data-processing systems. Existing UPSs include online UPSs, offline UPSs, line-interactive UPSs, as well as others. UPSs may provide output power to a load. The output power may be derived from a primary source of power, such as a utility-mains source, and/or derived from a back-up source of power, such as an energy-storage device.

Patent document <CIT> discloses a Soft Switched Voltage Source Inverter powered from a DC bus and implemented as an active neutral point clamped topology for use in a UPS. The UPS also comprises a battery connected to the DC bus through a DC-DC converter.

In one of the architectures, an energy storage system can be directly connected to the DC side of the inverter.

Patent document <CIT> discloses a Three-Level Two-Stage Decoupled Active NPC Converter.

At least one example in accordance with the present disclosure relates generally to power-conversion systems. Power devices such as uninterruptible power supplies (UPSs) may be used to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems and other data-processing systems. Existing UPSs include online UPSs, offline UPSs, line-interactive UPSs, as well as others. UPSs may provide output power to a load. The output power may be derived from a primary source of power, such as a utility-mains source, and/or derived from a back-up source of power, such as an energy-storage device.

According to at least one aspect of the present disclosure, a power system is provided comprising a power-system output configured to be coupled to, and provide an output AC waveform to, one or more loads, a positive DC bus, a negative DC bus, an inverter coupled to the positive DC bus and the negative DC bus, the inverter including an inverter output coupled to the power-system output, and a DC/DC converter coupled between the inverter output and at least one of the positive DC bus or the negative DC bus.

The disclosure is defined in the appended independent claims. Dependent claims constitute embodiments of the disclosure.

In some examples, the inverter is coupled between the positive DC bus and the negative DC bus and the DC/DC converter. In various examples, the inverter is configured to isolate the DC/DC converter from at least one of the positive DC bus or the negative DC bus. In at least one example, the power system includes at least one controller coupled to the inverter and the DC/DC converter, wherein the at least one controller is configured to control, during a positive portion of the output AC waveform, the inverter to isolate the DC/DC converter from the negative DC bus. In some examples, the at least one controller is further configured to control, during a negative portion of the output AC waveform, the inverter to isolate the DC/DC converter from the positive DC bus.

In various examples, the power system includes at least one controller coupled to the inverter and the DC/DC converter, wherein the power-system output is configured to provide an output AC waveform to the one or more loads, and wherein the at least one controller is configured to control, during a negative portion of the output AC waveform, the inverter to isolate the DC/DC converter from the positive DC bus. In at least one example, the inverter includes a first plurality of inverter switches coupled between at least one node and the positive DC bus and the negative DC bus, and a second plurality of inverter switches coupled between the at least one node and the inverter output. In some examples, the DC/DC converter includes a plurality of converter switches coupled to the at least one node.

In various examples, the power system includes at least one controller coupled to the inverter and the DC/DC converter, the at least one controller being configured to control, during a positive portion of the output AC waveform, the first plurality of inverter switches to couple the positive DC bus to the plurality of converter switches. In at least one example, the at least one controller is further configured to control, during the positive portion of the output AC waveform, the first plurality of inverter switches to isolate the negative DC bus from the plurality of converter switches. In some examples, the power system includes at least one controller coupled to the inverter and the DC/DC converter, the at least one controller being configured to control, during a negative portion of the output AC waveform, the first plurality of inverter switches to couple the negative DC bus to the plurality of converter switches.

In various examples, the power system includes at least one controller coupled to the inverter and the DC/DC converter, wherein the DC/DC converter includes a transformer, and wherein the at least one controller is configured to control the first plurality of inverter switches to couple the transformer to at most one of the positive DC bus or the negative DC bus at any time during at least a positive portion or a negative portion of the AC output waveform. In at least one example, the power system includes at least one controller coupled to the second plurality of inverter switches, wherein the at least one controller is configured to control the second plurality of inverter switches to produce a positive portion of the output AC waveform using DC power derived from the positive DC bus. In some examples, the at least one controller is configured to control the first plurality of inverter switches to couple the positive DC bus to the second plurality of inverter switches during the positive portion of the output AC waveform.

According to aspects of the disclosure, a method of controlling a power system including a positive DC bus, a negative DC bus, an output, an inverter, and a DC/DC converter coupled between the output and the inverter is provided, the method comprising controlling the inverter to provide an output AC waveform to the output, controlling, during a positive portion of the output AC waveform, the inverter to couple the positive DC bus to the DC/DC converter, and controlling, during the positive portion of the output AC waveform, the inverter to isolate the negative DC bus from the DC/DC converter.

In some examples, the method includes controlling, during a negative portion of the output AC waveform, the inverter to couple the negative DC bus to the DC/DC converter, and controlling, during the negative portion of the output AC waveform, the inverter to isolate the positive DC bus from the DC/DC converter. In various examples, the inverter includes at least one first inverter switch and at least one second inverter switch, and wherein controlling the inverter to couple the positive DC bus to the DC/DC converter includes closing the at least one first inverter switch, and controlling the inverter to isolate the negative DC bus from the DC/DC converter includes opening the at least one second inverter switch. In at least one example, the inverter includes at least one third inverter switch, and controlling the inverter to provide the output AC waveform to the output includes controlling the at least one third inverter switch to produce the output AC waveform using DC power derived from at least one of the positive DC bus or the negative DC bus.

According to aspects of the disclosure, a non-transitory computer-readable medium storing thereon sequences of computer-executable instructions for controlling a power system including a positive DC bus, a negative DC bus, an output, an inverter, and a DC/DC converter coupled between the output and the inverter is provided, the sequences of computer-executable instructions including instructions that instruct at least one processor to control the inverter to provide an output AC waveform to the output, control, during a positive portion of the output AC waveform, the inverter to couple the positive DC bus to the DC/DC converter, and control, during the positive portion of the output AC waveform, the inverter to isolate the negative DC bus from the DC/DC converter.

In some examples, the instructions further instruct the at least one processor to control, during a negative portion of the output AC waveform, the inverter to couple the negative DC bus to the DC/DC converter, and control, during the negative portion of the output AC waveform, the inverter to isolate the positive DC bus from the DC/DC converter.

According to aspects of the disclosure, a power system is provided comprising a power-system output configured to be coupled to, and provide an output AC waveform to, one or more loads, a positive DC bus, a negative DC bus, an inverter coupled to the positive DC bus and the negative DC bus, the inverter including an inverter output coupled to the power-system output, and a DC/DC converter coupled between the inverter output and at least one of the positive DC bus or the negative DC bus.

In at least one example, the positive DC bus and the negative DC bus are configured to be coupled to at least one energy-storage device. In at least one example, the DC/DC converter is configured to execute one or both of providing, via at least one of the positive DC bus or the negative DC bus, output power to the at least one energy-storage device, and receiving, via at least one of the positive DC bus or the negative DC bus, input power from the at least one energy-storage device. In at least one example, the output AC waveform includes a positive cycle and a negative cycle, and wherein the inverter is configured to provide, during the positive cycle, positive-voltage power to the DC/DC converter, and provide, during the negative cycle, negative-voltage power to the DC/DC converter.

In at least one example, the inverter includes a plurality of switches coupled between the inverter output and the power-system output. In at least one example, the inverter includes a snubber capacitor coupled in parallel with the plurality of switches. In at least one example, the inverter further comprises a first set of one or more inverter switches coupled to a positive-DC-power source at a first connection and to the plurality of switches at a second connection, and a second set of one or more inverter switches coupled to a negative-DC-power source at a third connection and to the plurality of switches at a fourth connection.

In at least one example, the inverter further comprises a first set of one or more inverter switches coupled to a positive-DC-power source at a first connection and to the inverter output at a second connection, and a second set of one or more inverter switches coupled to a negative-DC-power source at a third connection and to the inverter output at a fourth connection. In at least one example, the inverter further comprises a set of one or more inverter switches coupled to a power source at a first connection and to the inverter output at a second connection. In at least one example, the power source includes a capacitor, and wherein the set of one or more inverter switches is coupled in parallel with the capacitor.

In at least one example, the instructions further instruct the at least one processor to control, during a negative portion of the output AC waveform, the inverter to couple the negative DC bus to the DC/DC converter, and control, during the negative portion of the output AC waveform, the inverter to isolate the positive DC bus from the DC/DC converter. In at least one example, the instructions further instruct the at least one processor to control, during the negative portion of the output AC waveform, the DC/DC converter to provide power derived from the negative DC bus to at least one energy-storage device. In at least one example, the instructions further instruct the at least one processor to control, during the positive portion of the output AC waveform, the DC/DC converter to provide power derived from the positive DC bus to at least one energy-storage device.

In at least one example, the instructions further instruct the at least one processor to control, during the positive portion of the output AC waveform, the inverter to draw power from the positive DC bus, provide a first portion of the drawn power to the output, and provide a second portion of the drawn power to the DC/DC converter. In at least one example, the instructions further instruct the at least one processor to control, during the negative portion of the output AC waveform, the inverter to draw power from the negative DC bus, provide a first portion of the drawn power to the output, and provide a second portion of the drawn power to the DC/DC converter.

In at least one example, the method includes controlling, during a negative portion of the output AC waveform, the inverter to couple the negative DC bus to the DC/DC converter, and controlling, during the negative portion of the output AC waveform, the inverter to isolate the positive DC bus from the DC/DC converter. In at least one example, the method includes controlling, during the negative portion of the output AC waveform, the DC/DC converter to provide power derived from the negative DC bus to at least one energy-storage device. In at least one example, the method includes controlling, during the positive portion of the output AC waveform, the DC/DC converter to provide power derived from the positive DC bus to at least one energy-storage device.

Examples of the methods and systems discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and systems are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, components, elements and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples.

Any references to examples, embodiments, components, elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any embodiment, component, element or act herein may also embrace embodiments including only a singularity. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. In addition, in the event of inconsistent usages of terms between this document and documents incorporated herein by reference, the term usage in the incorporated features is supplementary to that of this document; for irreconcilable differences, the term usage in this document controls.

Uninterruptible power supplies (UPSs) are configured to provide uninterrupted power to one or more loads. An example UPS may draw power from at least one of several power sources. For example, a UPS may be coupled to a primary power source, such as a utility mains, and to a secondary power source, such as a battery. The primary power source may provide AC power to the UPS. The secondary power source may provide DC power to the UPS. The UPS may draw primary power (for example, AC power) from the primary power source when primary power is available (for example, when acceptable utility-mains power is available) and may draw DC power from the secondary power source when acceptable primary power is not available (for example, when the utility mains is experiencing a blackout condition). The UPS may use the primary and/or secondary power to provide output power to the one or more loads. The UPS may also use the primary power to recharge the secondary power source when, for example, the secondary power source is not fully charged.

The UPS may include power-conversion circuitry to process the primary power, secondary power, and output power. The UPS may also include at least one DC bus (for example, a positive DC bus and a negative DC bus) to interconnect the power-conversion circuitry. For example, the UPS may include an AC/DC converter coupled to the primary power source to convert primary AC power to DC bus power, a DC/DC converter coupled to the secondary power source to convert battery DC power to bus DC power, and a DC/AC inverter coupled to the one or more loads to convert DC bus power to output AC power. In some examples the DC/DC converter may be configured to only convert battery DC power to bus DC power (that is, the DC/DC converter may be "unidirectional"). Separate circuitry, which may be referred to as a "charger," may be provided to convert bus DC power to battery DC power to recharge the battery. In other examples the DC/DC converter may be configured to convert bus DC power to battery DC power (that is, recharging power) in addition to converting battery DC power to bus DC power (that is, the DC/DC converter may be "bidirectional"). A separate charger may thus be omitted in some examples.

One example of a DC/DC converter topology is the dual active bridge (DAB) converter topology, as described in greater detail below. DAB converters may be configured to support bidirectional power conversion between a battery and DC busses, which may be advantageous in certain UPS topologies. For example, DAB converters may be coupled to the positive DC bus and the negative DC bus of the UPS to not only provide bus DC power derived from the battery DC power, but also to draw bus DC power for conversion to battery DC power. However, in certain implementations, DAB converters may be susceptible to voltage imbalances on the positive and negative DC busses. For example, if a voltage imbalance exists between the positive and negative DC busses, a transformer of the DAB converter may become saturated and adversely impact performance of the DAB converter.

Examples of the disclosure provide a DC/AC inverter configured to provide positive-voltage DC power and negative-voltage DC power to a DC/DC converter. During a positive half-cycle of an output AC waveform, a DC/AC inverter may provide positive-voltage DC power to a DC/DC converter but isolate the DC/DC converter from the negative DC bus. During a negative half-cycle of the output AC waveform, the DC/AC inverter may provide negative-voltage DC power to the DC/DC converter but isolate the DC/DC converter from the positive DC bus. Accordingly, rather than being coupled directly to a positive DC bus and a negative DC bus simultaneously, the DC/DC converter may be alternately coupled to the positive DC bus and the negative DC bus. A risk of transformer saturation may therefore be reduced or eliminated by operating the DC/AC inverter to alternately provide positive- and negative-voltage DC power to the DC/DC converter, because a likelihood of imbalanced DC busses being continuously simultaneously coupled to the transformer is reduced or eliminated.

<FIG> is a block diagram of a UPS <NUM> according to an example. The UPS <NUM> includes an input <NUM>, an AC/DC converter <NUM>, one or more DC busses <NUM>, a DC/DC converter <NUM>, an energy-storage-device interface <NUM>, at least one controller <NUM> ("controller <NUM>"), a DC/AC inverter <NUM>, an output <NUM> (also referred to as a "power-system output"), a memory and/or storage <NUM>, one or more communication interfaces <NUM> ("communication interfaces <NUM>"), which may be communicatively coupled to one or more external systems <NUM> ("external systems <NUM>"), and one or more voltage sensors and/or current sensors <NUM> ("sensors <NUM>").

The input <NUM> is coupled to the AC/DC converter <NUM> and to an AC power source (not pictured), such as an AC mains power supply. The AC/DC converter <NUM> is coupled to the input <NUM> and to the one or more DC busses <NUM>, and is communicatively coupled to the controller <NUM>. The one or more DC busses <NUM> are coupled to the AC/DC converter <NUM>, the DC/DC converter <NUM>, and to the DC/AC inverter <NUM>, and are communicatively coupled to the controller <NUM>. The DC/DC converter <NUM> is coupled to the one or more DC busses <NUM> and to the energy-storage-device interface <NUM>, and is communicatively coupled to the controller <NUM>. The energy-storage-device interface <NUM> is coupled to the DC/DC converter <NUM>, and is configured to be coupled to at least one energy-storage device <NUM> and/or another energy-storage device. In some examples, the energy-storage-device interface <NUM> is configured to be communicatively coupled to the controller <NUM>.

In some examples, the UPS <NUM> may be external to the at least one energy-storage device <NUM> and may be coupled to the at least one energy-storage device <NUM> via the energy-storage-device interface <NUM>. In various examples, the UPS <NUM> may include one or more energy-storage devices, which may include the energy-storage device <NUM>. The energy-storage device <NUM> may include one or more batteries, capacitors, flywheels, or other energy-storage devices in various examples.

The DC/AC inverter <NUM> is coupled to the one or more DC busses <NUM> and to the output <NUM>, and is communicatively coupled to the controller <NUM>. The output <NUM> is coupled to the DC/AC inverter <NUM>, and to an external load (not pictured). The controller <NUM> is communicatively coupled to the AC/DC converter <NUM>, the one or more DC busses <NUM>, the DC/DC converter <NUM>, the energy-storage-device interface <NUM>, the DC/AC inverter <NUM>, the memory and/or storage <NUM>, the communication interfaces <NUM>, and/or the energy-storage device <NUM>. The sensors <NUM> are communicatively coupled to the controller <NUM> and may be coupled to one or more other components of the UPS <NUM>, such as the input <NUM>, the AC/DC converter <NUM>, the one or more DC busses <NUM>, the DC/DC converter <NUM>, the energy-storage-device interface <NUM>, the DC/AC inverter <NUM>, and/or the output <NUM>.

The input <NUM> is configured to be coupled to an AC mains power source and to receive input AC power having an input voltage level. The UPS <NUM> is configured to operate in different modes of operation based on the input voltage of the AC power provided to the input <NUM>. The controller <NUM> may determine a mode of operation in which to operate the UPS <NUM> based on whether the input voltage of the AC power is acceptable. The controller <NUM> may include or be coupled to one or more sensors, such as the sensors <NUM>, configured to sense parameters of the input voltage. For example, the sensors <NUM> may include one or more voltage and/or current sensors coupled to the input <NUM> and being configured to sense information indicative of a voltage at the input <NUM> and provide the sensed information to the controller <NUM>.

When AC power provided to the input <NUM> is acceptable (for example, by having parameters, such as an input voltage value, that meet specified values, such as by falling within a range of acceptable input voltage values), the controller <NUM> controls components of the UPS <NUM> to operate in an online mode of operation, or "normal mode of operation. " In the normal mode of operation, AC power received at the input <NUM> is provided to the AC/DC converter <NUM>. The AC/DC converter <NUM> converts the AC power into DC power and provides the DC power to the one or more DC busses <NUM>. The one or more DC busses <NUM> distribute the DC power to the DC/DC converter <NUM> and to the DC/AC inverter <NUM>. The DC/DC converter <NUM> converts the received DC power and provides the converted DC power to the energy-storage-device interface <NUM>. The energy-storage-device interface <NUM> receives the converted DC power, and provides the converted DC power to the energy-storage device <NUM> to charge the energy-storage device <NUM>. The DC/AC inverter <NUM> receives DC power from the one or more DC busses <NUM>, converts the DC power into regulated AC power, and provides the regulated AC power to the output <NUM> to be delivered to a load.

When AC power provided to the input <NUM> from the AC mains power source is not acceptable (for example, by having parameters, such as an input voltage value, that do not meet specified values, such as by falling outside of a range of acceptable input voltage values), the controller <NUM> controls components of the UPS <NUM> to operate in a backup mode of operation, which may be referred to as an "on-battery mode of operation" in some examples. In the backup mode of operation, DC power is discharged from the energy-storage device <NUM> to the energy-storage-device interface <NUM>, and the energy-storage-device interface <NUM> provides the discharged DC power to the DC/DC converter <NUM>. The DC/DC converter <NUM> converts the received DC power and distributes the DC power amongst the one or more DC busses <NUM>. For example, the DC/DC converter <NUM> may evenly distribute the power amongst the one or more DC busses <NUM>. The one or more DC busses <NUM> provide the received power to the DC/AC inverter <NUM>. The DC/AC inverter <NUM> receives the DC power from the one or more DC busses <NUM>, converts the DC power into regulated AC power, and provides the regulated AC power to the output <NUM>.

In some examples, the sensors <NUM> may include one or more sensors coupled to one or more of the foregoing components such that a voltage and/or current of one or more of the foregoing components may be determined by the controller <NUM>. The controller <NUM> may store information in, and/or retrieve information from, the memory and/or storage <NUM>. For example, the controller <NUM> may store information indicative of sensed parameters (for example, input-voltage values of the AC power received at the input <NUM>) in the memory and/or storage <NUM>. The controller <NUM> may further receive information from, or provide information to, the communication interfaces <NUM>. The communication interfaces <NUM> may include one or more communication interfaces including, for example, user interfaces (such as display screens, touch-sensitive screens, keyboards, mice, track pads, dials, buttons, switches, sliders, light-emitting components such as light-emitting diodes, sound-emitting components such as speakers, buzzers, and so forth configured to output sound inside and/or outside of a frequency range audible to humans, and so forth), wired communication interfaces (such as wired ports), wireless communication interfaces (such as antennas), and so forth, configured to exchange information with one or more systems, such as the external systems <NUM>, or other entities, such as human beings. The external systems <NUM> may include any device, component, module, and so forth, that is external to the UPS <NUM>, such as a server, database, laptop computer, desktop computer, tablet computer, smartphone, central controller or data-aggregation system, other UPSs, and so forth.

<FIG> illustrates a schematic diagram of the DC/DC converter <NUM> according to an example. The DC/DC converter <NUM> may be implemented according to any of various topologies. <FIG> illustrates one example of the DC/DC converter <NUM> implemented according to a DAB topology. However, the DC/DC converter <NUM> is not limited to implementation in a DAB topology, and the illustrated topology is provided for purposes of example only.

The DC/DC converter <NUM> includes a first bus capacitor <NUM>, a second bus capacitor <NUM>, a first switching device <NUM>, a second switching device <NUM>, a first inductor <NUM>, a second inductor <NUM>, a transformer <NUM>, a third switching device <NUM>, a fourth switching device <NUM>, a fifth switching device <NUM>, a sixth switching device <NUM>, and an output capacitor <NUM>. The DC/DC converter <NUM> is coupled to a positive DC bus 106a and a negative DC bus 106b, which may be implementations of the one or more DC busses <NUM>. The DC/DC converter <NUM> is also coupled to a first energy-storage-device-interface connection 110a and a second energy-storage-device-interface connection 110b, which may be implementations of the energy-storage-device interface <NUM>.

The DC/DC converter <NUM> may operate as a two-stage converter. A first stage includes the first switching device <NUM> and the second switching device <NUM>, which may be configured in a half-bridge topology. A second stage includes the third switching device <NUM>, the fourth switching device <NUM>, the fifth switching device <NUM>, and the sixth switching device <NUM>, which may be configured in a full-bridge topology. The first stage is connected to the second stage via the transformer <NUM>.

The controller <NUM> may operate the switching devices <NUM>, <NUM>, <NUM>-<NUM> to convert, via the transformer <NUM>, bus DC power received from the DC busses 106a, 106b to battery DC power provided to the energy-storage-device-interface connections 110a, 110b. Similarly, the controller <NUM> may operate the switching devices <NUM>, <NUM>, <NUM>-<NUM> to convert, via the transformer <NUM>, battery DC power received from the energy-storage-device-interface connections 110a, 110b to bus DC power provided to the DC busses 106a, 106b.

As discussed above, however, DAB converters may be susceptible to DC-bus-voltage imbalances. For example, if a voltage on the positive DC bus 106a is not balanced with a voltage on the negative DC bus 106b (for example, by not having a substantially equal voltage magnitude relative to a common node, such as ground), the transformer <NUM> may become saturated. Performance of the transformer <NUM> may be adversely impacted by saturation. As discussed in greater detail below, a risk of saturation of the transformer <NUM> may be reduced by integrating the DC/DC converter <NUM> with the DC/AC inverter <NUM>.

<FIG> illustrates a schematic diagram of the DC/AC inverter <NUM> implemented according to an active neutral-point clamped (ANPC) topology.

The DC/AC inverter <NUM> includes a first bus capacitor <NUM>, a second bus capacitor <NUM>, a first inverter switching device <NUM>, a second inverter switching device <NUM>, a third inverter switching device <NUM>, a fourth inverter switching device <NUM>, a snubber capacitor <NUM>, a fifth inverter switching device <NUM>, and a sixth inverter switching device <NUM>. The DC/AC inverter <NUM> is coupled to the positive DC bus 106a and the negative DC bus 106b. The DC/AC inverter <NUM> is also coupled to the output <NUM>.

The DC/AC inverter <NUM> operates as a two-stage inverter. A first stage may include the first inverter switching device <NUM>, the second inverter switching device <NUM>, the third inverter switching device <NUM>, and the fourth inverter switching device <NUM>. The first-stage inverter switching devices <NUM>-<NUM> may be implemented as IGBT switches in some examples. A second stage may include the fifth inverter switching device <NUM> and the sixth inverter switching device <NUM>. The second-stage inverter switching devices <NUM>, <NUM> may be implemented as MOSFET switches in some examples.

The controller <NUM> may operate the switching devices <NUM>-<NUM>, <NUM>, <NUM> to convert bus DC power from the DC busses <NUM> to AC output power provided to one or more loads at the output <NUM>. The controller <NUM> may operate the switching devices <NUM>-<NUM>, <NUM>, <NUM> according to any of various modulation schemes. In one example, the controller <NUM> may operate the first stage including the switching devices <NUM>-<NUM> at a line frequency to alternately couple the positive DC bus 106a and the negative DC bus 106b to the switching devices <NUM>, <NUM>. For example, the controller <NUM> may close the first inverter switching device <NUM> and the third inverter switching device <NUM> to couple the positive DC bus 106a to the switching devices <NUM>, <NUM> during a positive portion of an output AC waveform. The controller <NUM> may close the second inverter switching device <NUM> and the fourth inverter switching device <NUM> to couple the negative DC bus 106b to the switching devices <NUM>, <NUM> during a negative portion of the output AC waveform. By alternately coupling the switching devices <NUM>, <NUM> and the switching devices <NUM>, <NUM> to the snubber capacitor <NUM>, a voltage across the snubber capacitor <NUM> may be a substantially DC voltage and, in some cases, may exhibit a small AC portion pulsing at line frequency if the DC busses 106a, 106b are imbalanced. The controller <NUM> may operate the second stage including the switching devices <NUM>, <NUM> at a high frequency with varying pulse widths to produce AC power from the alternate positive DC-voltage power and negative DC-voltage power received from the first stage. The snubber capacitor <NUM> may negate at least a portion of stray inductance during operation of the switching devices <NUM>-<NUM>, <NUM>, <NUM>.

In other examples, the controller <NUM> may implement different modulation schemes. For example, rather than operating the first-stage inverter switching devices <NUM>-<NUM> at a low frequency and the second-stage inverter switching devices <NUM>, <NUM> at a high frequency, the controller <NUM> may operate the first-stage inverter switching devices <NUM>-<NUM> at a high frequency and the second-stage inverter switching devices <NUM>, <NUM> at a low frequency. Accordingly, operation of the DC/AC inverter <NUM> is not limited to a single operation scheme.

As illustrated in <FIG> and <FIG>, the DC/DC converter <NUM> and the DC/AC inverter <NUM> may each be coupled directly to the one or more DC busses <NUM>. As discussed above, the DC/DC converter <NUM> may be sensitive to voltage imbalances on the one or more DC busses <NUM> in certain implementations (for example, as discussed above), which may cause saturation of the transformer <NUM>. Also as discussed above, the DC/AC inverter <NUM> may alternately couple the positive DC bus 106a and the negative DC bus 106b to the switching devices <NUM>, <NUM> to convert the positive-voltage DC power and the negative-voltage DC power to AC power.

A topology of the DC/DC converter <NUM> and the DC/AC inverter <NUM> are integrated together such that the DC/DC converter <NUM> is coupled to the DC busses <NUM> via the DC/AC inverter <NUM>. Rather than the DC/DC converter <NUM> being coupled directly to the DC busses <NUM>, the DC/AC inverter <NUM> may alternately couple the positive DC bus 106a and the negative DC bus 106b to the DC/DC converter <NUM> in a similar manner that the DC/AC inverter <NUM> alternately couples the DC busses 106a, 106b to the second-stage inverter switching devices <NUM>, <NUM>. Accordingly, a risk of saturation of the transformer <NUM> may be significantly reduced or eliminated.

<FIG> illustrates a block diagram of a UPS <NUM> according to an example. The UPS <NUM> may include substantially similar or identical blocks of components as the UPS <NUM>, though the blocks of components may be implemented according to different topologies. Furthermore, components of the UPS <NUM> may be coupled differently than the components of the UPS <NUM>.

For example, the UPS <NUM> includes the one or more DC busses <NUM>, the DC/AC inverter <NUM>, and the DC/DC converter <NUM>. However, whereas the DC/DC converter <NUM> is coupled directly to the one or more DC busses <NUM> in the UPS <NUM>, the DC/DC converter <NUM> is coupled to the one or more DC busses <NUM> via the DC/AC inverter <NUM> in the UPS <NUM>. The controller <NUM> may control the DC/AC inverter <NUM> to alternately couple the positive DC bus 106a and the negative DC bus 106b to the DC/DC converter <NUM> in the UPS <NUM>. In this manner, the controller <NUM> may reduce a risk of saturation of the transformer <NUM> of the DC/DC converter <NUM>.

<FIG> illustrates a schematic diagram of components of the UPS <NUM> according to an example. For example, <FIG> illustrates the positive DC bus 106a, the negative DC bus 106b, the DC/DC converter <NUM>, the first energy-storage-device-interface connection 110a, the second energy-storage-device-interface connection 110b, the DC/AC inverter <NUM>, and the output <NUM>. The DC/AC inverter <NUM> is configured in a two-stage topology substantially similar or identical to the topology illustrated in <FIG>. The DC/DC converter <NUM> is configured in a two-stage topology similar to, but different from, the topology of <FIG>. For example, whereas the topology of the DC/DC converter <NUM> in <FIG> implements a half bridge as the first stage, the topology of the DC/DC converter <NUM> in <FIG> implements a full bridge as the first stage. The principles of the disclosure are applicable to a wide variety of converter topologies and are not limited to the illustrated topologies, which are provided for purposes of example.

In one example, the DC/DC converter <NUM> of <FIG> includes a first converter switching device <NUM>, a second converter switching device <NUM>, a third converter switching device <NUM>, a fourth converter switching device <NUM>, an inductor <NUM>, a transformer <NUM>, a fifth converter switching device <NUM>, a sixth converter switching device <NUM>, a seventh converter switching device <NUM>, and an eighth converter switching device <NUM>. As discussed above with respect to <FIG>, the DC/AC inverter <NUM> includes the first bus capacitor <NUM>, the second bus capacitor <NUM>, the first inverter switching device <NUM>, the second inverter switching device <NUM>, the third inverter switching device <NUM>, the fourth inverter switching device <NUM>, the snubber capacitor <NUM>, the fifth inverter switching device <NUM>, and the sixth inverter switching device <NUM>. The UPS <NUM> further includes an output filter including an output inductor <NUM> and an output capacitor <NUM>.

The first bus capacitor <NUM> is coupled to the positive DC bus 106a at a first connection, and is coupled to a reference node <NUM> (for example, a neutral node, return node, and/or ground node) at a second connection. The second bus capacitor <NUM> is coupled to the reference node <NUM> at a first connection, and is coupled to the negative DC bus 106b at a second connection.

The first inverter switching device <NUM> is coupled to the positive DC bus 106a at a first connection, and is coupled to the second inverter switching device <NUM>, the snubber capacitor <NUM>, the fifth inverter switching device <NUM>, the first converter switching device <NUM>, and the third converter switching device <NUM> at a second connection. The first inverter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The second inverter switching device <NUM> is coupled to the first inverter switching device <NUM>, the snubber capacitor <NUM>, the fifth inverter switching device <NUM>, the first converter switching device <NUM>, and the third converter switching device <NUM> at a first connection, and is coupled to the reference node <NUM> at a second connection. The second inverter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The third inverter switching device <NUM> is coupled to the reference node <NUM> at a first connection, and is coupled to the fourth inverter switching device <NUM>, the snubber capacitor <NUM>, the sixth inverter switching device <NUM>, the second converter switching device <NUM>, and the fourth converter switching device <NUM> at a second connection. The third inverter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The fourth inverter switching device <NUM> is coupled to the third inverter switching device <NUM>, the snubber capacitor <NUM>, the sixth inverter switching device <NUM>, the second converter switching device <NUM>, and the fourth converter switching device <NUM> at a first connection, and is coupled to the negative DC bus 106b at a second connection. The fourth inverter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The snubber capacitor <NUM> is coupled to the first inverter switching device <NUM>, the second inverter switching device <NUM>, the fifth inverter switching device <NUM>, the first converter switching device <NUM>, and the third converter switching device <NUM> at a first connection, and is coupled to the third inverter switching device <NUM>, the fourth inverter switching device <NUM>, the sixth inverter switching device <NUM>, the second converter switching device <NUM>, and the fourth converter switching device <NUM> at a second connection.

The fifth inverter switching device <NUM> is coupled to the first inverter switching device <NUM>, the second inverter switching device <NUM>, the snubber capacitor <NUM>, the first converter switching device <NUM>, and the third converter switching device <NUM> at a first connection, and is coupled to the output inductor <NUM> at a second connection (for example, via an inverter output between the switching devices <NUM>, <NUM> and the output inductor <NUM>). The fifth inverter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The sixth inverter switching device <NUM> is coupled to the third inverter switching device <NUM>, the fourth inverter switching device <NUM>, the snubber capacitor <NUM>, the second converter switching device <NUM>, and the fourth converter switching device <NUM> at a first connection, and is coupled to the output inductor <NUM> at a second connection (for example, via the inverter output connection). The sixth inverter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The first converter switching device <NUM> is coupled to the first inverter switching device <NUM>, the second inverter switching device <NUM>, the snubber capacitor <NUM>, and the fifth inverter switching device <NUM> at a first connection, and is coupled to the second converter switching device <NUM> and the inductor <NUM> at a second connection. The first converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>. The DC/DC converter <NUM> may therefore be coupled between the positive DC bus 106a and the inverter output at least inasmuch as the first connection of the first converter switching device <NUM> is coupled to the positive DC bus 106a via the first inverter switching device <NUM> and to the inverter output via the fifth inverter switching device <NUM>.

The second converter switching device <NUM> is coupled to the first converter switching device <NUM> and the inductor <NUM> at a first connection, and is coupled to the third inverter switching device <NUM>, the fourth inverter switching device <NUM>, the snubber capacitor <NUM>, and the sixth inverter switching device <NUM> at a second connection. The second converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>. The DC/DC converter <NUM> may therefore be coupled between the negative DC bus 106b and the inverter output at least inasmuch as the second connection of the second converter switching device <NUM> is coupled to the negative DC bus 106b via the fourth inverter switching device <NUM> and to the inverter output via the sixth inverter switching device <NUM>.

The third converter switching device <NUM> is coupled to the first inverter switching device <NUM>, the second inverter switching device <NUM>, the snubber capacitor <NUM>, and the fifth inverter switching device <NUM> at a first connection, and is coupled to the fourth converter switching device <NUM> and a non-dotted pole of a primary winding of the transformer <NUM> at a second connection. The third converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>. The DC/DC converter <NUM> may therefore be coupled between the positive DC bus 106a and the inverter output at least inasmuch as the first connection of the third converter switching device <NUM> is coupled to the positive DC bus 106a via the first inverter switching device <NUM> and to the inverter output via the fifth inverter switching device <NUM>.

The fourth converter switching device <NUM> is coupled to the third converter switching device <NUM> and the non-dotted pole of the primary winding of the transformer <NUM> at a first connection, and is coupled to the third inverter switching device <NUM>, the fourth inverter switching device <NUM>, the snubber capacitor <NUM>, and the sixth inverter switching device <NUM> at a second connection. The fourth converter switching device <NUM> is communicatively coupled to the controller <NUM>. The DC/DC converter <NUM> may therefore be coupled between the negative DC bus 106b and the inverter output at least inasmuch as the second connection of the fourth converter switching device <NUM> is coupled to the negative DC bus 106b via the fourth inverter switching device <NUM> and to the inverter output via the sixth inverter switching device <NUM>.

The inductor <NUM> is coupled to the first converter switching device <NUM> and the second converter switching device <NUM> at a first connection, and is coupled to a dotted pole of the primary winding of the transformer <NUM> at a second connection. The transformer <NUM> includes the primary winding having the dotted pole coupled to the inductor <NUM> and the non-dotted pole coupled to the third converter switching device <NUM> and the fourth converter switching device <NUM>. The transformer <NUM> further includes a secondary winding inductively coupled to the primary winding and having a dotted pole coupled to the fifth converter switching device <NUM> and the sixth converter switching device <NUM>, and a non-dotted pole coupled to the seventh converter switching device <NUM> and the eighth converter switching device <NUM>.

The fifth converter switching device <NUM> is coupled to the first energy-storage-device-interface connection 110a at a first connection, and is coupled to the dotted pole of the secondary winding of the transformer <NUM> and the second converter switching device <NUM> at a second connection. The fifth converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The sixth converter switching device <NUM> is coupled to the fifth converter switching device <NUM> and the dotted pole of the secondary winding of the transformer <NUM> at a first connection, and is coupled to the second energy-storage-device-interface connection 110b at a second connection. The sixth converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The seventh converter switching device <NUM> is coupled to the first energy-storage-device-interface connection 110a at a first connection, and is coupled to the non-dotted pole of the secondary winding of the transformer <NUM> and the eighth converter switching device <NUM> at a second connection. The seventh converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The eighth converter switching device <NUM> is coupled to the seventh converter switching device <NUM> and the non-dotted pole of the secondary winding of the transformer <NUM> at a first connection, and is coupled to the second energy-storage-device-interface connection 110b at a second connection. The eighth converter switching device <NUM> is configured to be communicatively coupled to the controller <NUM>.

The output inductor <NUM> is coupled to the fifth inverter switching device <NUM> and the sixth inverter switching device <NUM> (for example, via the inverter output) at a first connection, and is coupled to the output capacitor <NUM> and the output <NUM> at a second connection. The output capacitor <NUM> is coupled to the output inductor <NUM> and the output <NUM> at a first connection, and is coupled to the reference node <NUM> at a second connection.

The positive DC bus 106a is coupled to the first bus capacitor <NUM> and the first inverter switching device <NUM>. The positive DC bus 106a may be coupled to additional components not illustrated in <FIG>, such as the AC/DC converter <NUM>, which are omitted for purposes of clarity. The negative DC bus 106b is coupled to the second bus capacitor <NUM> and the fourth inverter switching device <NUM>. The negative DC bus 106b may be coupled to additional components not illustrated in <FIG>, such as the AC/DC converter <NUM>, which are omitted for purposes of clarity.

The first energy-storage-device-interface connection 110a is coupled to the fifth converter switching device <NUM> and the seventh converter switching device <NUM>, and is configured to be coupled to a positive terminal of the energy-storage device <NUM>. The second energy-storage-device-interface connection 110b is coupled to the sixth converter switching device <NUM> and the eighth converter switching device <NUM>, and is configured to be coupled to a negative terminal of the energy-storage device <NUM>.

The output <NUM> is coupled to the output inductor <NUM> and the output capacitor <NUM>. The output <NUM> may be coupled to additional components or devices not illustrated in <FIG>, such as one or more loads, which are omitted for purposes of clarity. The energy-storage device <NUM> is configured to be coupled to the first energy-storage-device-interface connection 110a at the positive terminal, and is configured to be coupled to the second energy-storage-device-interface connection 110b at the negative terminal.

As discussed above, the controller <NUM> may operate the DC/AC inverter <NUM> to alternately provide positive-voltage DC power and negative-voltage DC power to the DC/DC converter <NUM>. <FIG> illustrates a process <NUM> of operating the UPS <NUM> according to an example. The process <NUM> may be executed by the controller <NUM>. For example, the UPS <NUM> may include one or more computer-readable media storing instructions thereon that, when executed by the controller <NUM>, cause the controller <NUM> to execute the process <NUM>.

At act <NUM>, the controller <NUM> begins operating the UPS <NUM> to output a positive half-cycle of an output AC waveform. For example, the UPS <NUM> may output the AC waveform to one or more loads at the output <NUM>. The AC waveform may include a positive half-cycle and a negative half-cycle in some examples. In other examples, the AC waveform may include a positive portion and a negative portion in which the positive portion makes up greater than or less than half of the AC waveform and the negative portion makes up at least part of a remainder of the AC waveform. For purposes of explanation, examples are provided in which the AC waveform includes a positive half-cycle and a negative half-cycle.

At act <NUM>, the controller <NUM> controls the first inverter switching device <NUM> and the third inverter switching device <NUM> to be closed and conducting. Closing the inverter switching devices <NUM>, <NUM> couples the first bus capacitor <NUM> and the positive DC bus 106a to the inverter switching devices <NUM>, <NUM> and the DC/DC converter <NUM>, thereby applying a positive DC voltage to the inverter switching devices <NUM>, <NUM> and to the DC/DC converter <NUM>. As discussed below, act <NUM> describes operating the inverter switching devices <NUM>, <NUM> using the positive DC voltage, and act <NUM> describes operating the DC/DC converter <NUM> using the positive DC voltage. The controller <NUM> may control the second inverter switching device <NUM> and the fourth inverter switching device <NUM> to remain (or transition to) open and non-conducting to isolate the DC/DC converter <NUM> from the negative DC bus 106b, which may include not controlling the second inverter switching device <NUM> and the fourth inverter switching device <NUM> to be closed and conducting (for example, if the inverter switching devices <NUM>, <NUM> are normally open).

At act <NUM>, the controller <NUM> operates the fifth inverter switching device <NUM> and/or the sixth inverter switching device <NUM> to produce the positive half-cycle of the output AC waveform. For example, the controller <NUM> may control the fifth inverter switching device <NUM> to alternately open and close at a relatively high frequency (for example, compared to the line frequency of the output AC waveform) to produce the positive half-cycle of the output AC waveform. Closing the fifth inverter switching device <NUM> couples the output <NUM> (for example, via the output inductor <NUM>) to the positive DC bus 106a via the first inverter switching device <NUM> and the fifth inverter switching device <NUM>, thereby enabling positive-voltage power to pass from the positive DC bus 106a to the output <NUM>. The controller <NUM> may therefore produce a desired positive half-cycle AC output waveform using positive-voltage DC power received from the positive DC bus 106a by controlling the fifth inverter switching device <NUM> and/or the sixth inverter switching device <NUM>.

At act <NUM>, the controller <NUM> operates the DC/DC converter <NUM> to convert DC power using the positive-voltage DC power provided from the positive DC bus 106a via the first inverter switching device <NUM> and the third inverter switching device <NUM>. Act <NUM> may be optionally executed in examples in which the energy-storage device <NUM> is not fully charged, such that it might be desirable to provide recharging power to the energy-storage device <NUM>. If the controller <NUM> determines that the energy-storage device <NUM> is fully charged or otherwise above a recharging-threshold state of charge (SOC), act <NUM> may not be executed. In some examples, a voltage level of the one or more DC busses <NUM> (for example, about <NUM> V) may be substantially higher than a voltage level of the energy-storage device <NUM> (for example, about <NUM> V). Accordingly, the DC/DC converter <NUM> may step down bus DC voltage to battery DC voltage, and may step up battery DC voltage to bus DC voltage.

Act <NUM> may include coupling the positive DC bus 106a to the primary winding of the transformer <NUM> to induce a current in the secondary winding of the transformer <NUM>. For example, the controller <NUM> may control the converter switching devices <NUM>, <NUM> to be closed at a first point in time, and may control the converter switching devices <NUM>, <NUM> to be closed at a second point in time, such that the positive voltage is alternately applied across the poles of the primary winding of the transformer <NUM>. The controller <NUM> may operate the converter switching devices <NUM>-<NUM> in a similar manner to provide the induced current to the energy-storage device <NUM> as a recharging current.

Because the DC/DC converter <NUM> is coupled to the positive DC bus 106a via the closed inverter switching devices <NUM>, <NUM>, but is isolated from the negative DC bus 106b by the open inverter switching devise <NUM>, <NUM>, a risk of saturation of the transformer <NUM> due to a voltage imbalance on the DC busses 106a, 106b is reduced or eliminated. Accordingly, the controller <NUM> may operate the DC/DC converter <NUM> to provide a recharging current derived from the positive DC bus 106a to the energy-storage device <NUM> with a minimized or eliminated risk of saturation of the transformer <NUM>.

At act <NUM>, the controller <NUM> determines whether the positive half-cycle of the output AC waveform is complete. For example, the controller <NUM> may determine if half a period of the output AC waveform has elapsed since beginning to provide the negative half-cycle of the output AC waveform at act <NUM>. If the positive half-cycle of the output AC waveform is not complete (<NUM> NO), the process <NUM> returns to act <NUM>. Acts <NUM>-<NUM> are repeated until a determination is made that the positive half-cycle of the output AC waveform is complete (<NUM> YES), at which point the process <NUM> continues to act <NUM>. Act <NUM> is not described as being repeated at least because the controller <NUM> may control the inverter switching devices <NUM>, <NUM> to remain closed as acts <NUM>-<NUM> are repeatedly executed, that is, the inverter switching devices <NUM>, <NUM> need not be closed again while acts <NUM>-<NUM> are repeatedly executed.

At act <NUM>, the controller <NUM> begins operating the UPS <NUM> to output a negative half-cycle of an output AC waveform.

At act <NUM>, the controller <NUM> controls the second inverter switching device <NUM> and the fourth inverter switching device <NUM> to be closed and conducting. Closing the inverter switching devices <NUM>, <NUM> couples the second bus capacitor <NUM> and the negative DC bus 106b to the inverter switching devices <NUM>, <NUM>, thereby applying a negative DC voltage to the inverter switching devices <NUM>, <NUM> and to the DC/DC converter <NUM>. As discussed below, act <NUM> describes operating the inverter switching devices <NUM>, <NUM> using the negative DC voltage, and act <NUM> describes operating the DC/DC converter <NUM> using the negative DC voltage. The controller <NUM> may control the first inverter switching device <NUM> and the third inverter switching device <NUM> to remain (or transition to) open and non-conducting to isolate the DC/DC converter <NUM> from the positive DC bus 106a, which may include not controlling the first inverter switching device <NUM> and the third inverter switching device <NUM> to be closed and conducting (for example, if the inverter switching devices <NUM>, <NUM> are normally open).

At act <NUM>, the controller <NUM> operates the fifth inverter switching device <NUM> and/or the sixth inverter switching device <NUM> to produce the negative half-cycle of the output AC waveform. For example, the controller <NUM> may control the sixth inverter switching device <NUM> to alternately open and close at a relatively high frequency (for example, compared to the line frequency of the output AC waveform) to produce the negative half-cycle of the output AC waveform. Closing the sixth inverter switching device <NUM> couples the output <NUM> (for example, via the output inductor <NUM>) to the negative DC bus 106b via the fourth inverter switching device <NUM> and the sixth inverter switching device <NUM>, thereby enabling negative-voltage power to pass from the negative DC bus 106b to the output <NUM>. The controller <NUM> may therefore produce a desired negative half-cycle AC output waveform using negative-voltage DC power received from the negative DC bus 106b by controlling the fifth inverter switching device <NUM> and/or the sixth inverter switching device <NUM>.

At act <NUM>, the controller <NUM> operates the DC/DC converter <NUM> to convert DC power using the negative-voltage DC power provided from the negative DC bus 106b via the second inverter switching device <NUM> and the fourth inverter switching device <NUM>. Act <NUM> may be optionally executed in examples in which the energy-storage device <NUM> is not fully charged, such that it might be desirable to provide recharging power to the energy-storage device <NUM>. If the energy-storage device <NUM> is fully charged or otherwise above a recharging-threshold state of charge (SOC), act <NUM> may not be executed.

Act <NUM> may include coupling the negative DC bus 106b to the primary winding of the transformer <NUM> to induce a current in the secondary winding of the transformer <NUM>. For example, the controller <NUM> may control the converter switching devices <NUM>, <NUM> to be closed at a first point in time, and may control the converter switching devices <NUM>, <NUM> to be closed at a second point in time, such that the negative voltage is alternately applied across the poles of the primary winding of the transformer <NUM>. The controller <NUM> may operate the converter switching devices <NUM>-<NUM> in a similar manner to provide the induced current to the energy-storage device <NUM> as a recharging current.

Because the DC/DC converter <NUM> is coupled to the negative DC bus 106b via the closed inverter switching devices <NUM>, <NUM>, but is isolated from the positive DC bus 106a by the open inverter switching devise <NUM>, <NUM>, a risk of saturation of the transformer <NUM> due to a voltage imbalance on the DC busses 106a, 106b is reduced or eliminated. Accordingly, the controller <NUM> may operate the DC/DC converter <NUM> to provide a recharging current derived from the negative DC bus 106b to the energy-storage device <NUM> with a minimized or eliminated risk of saturation of the transformer <NUM>.

At act <NUM>, the controller <NUM> determines whether the negative half-cycle of the output AC waveform is complete. For example, the controller <NUM> may determine if half a period of the output AC waveform has elapsed since beginning to provide the negative half-cycle of the output AC waveform at act <NUM>. If the negative half-cycle of the output AC waveform is not complete (<NUM> NO), the process <NUM> returns to act <NUM>. Acts <NUM>-<NUM> are repeated until a determination is made that the negative half-cycle of the output AC waveform is complete (<NUM> YES), at which point the process <NUM> returns to act <NUM>. Act <NUM> is not described as being repeated at least because the controller <NUM> may control the inverter switching devices <NUM>, <NUM> to remain closed as acts <NUM>-<NUM> are repeatedly executed, that is, the inverter switching devices <NUM>, <NUM> need not be closed again while acts <NUM>-<NUM> are repeatedly executed. The process <NUM> may then be repeated.

According, the process <NUM> provides a method for the controller <NUM> to control the inverter switching devices <NUM>-<NUM> to alternately provide positive-voltage DC power and negative-voltage DC power to the inverter switching devices <NUM>, <NUM> and the DC/DC converter <NUM>. By alternately coupling the positive and negative DC busses 106a, 106b to the DC/DC converter <NUM>, rather than maintaining a direct connection between the DC busses 106a, 106b and the DC/DC converter <NUM>, a risk of transformer saturation may be eliminated or reduced. Additionally, in various examples the switching device <NUM>-<NUM> and the transformer <NUM> may be subjected to a voltage drop from either of the DC busses 106a, 106b to the reference node <NUM>, rather than a voltage drop from one of the DC busses 106a, 106b to the other, which may provide for a reduction in losses, cost, and size of components.

Although certain examples of the DC/DC converter <NUM> have been provided for purposes of explanation, the principles of the disclosure are not limited to the example implementations of the DC/DC converter <NUM>. Although <FIG> illustrates an example in which the DC/DC converter <NUM> is implemented as a bidirectional DAB converter, alternative DC/DC converter topologies may be implemented, including unidirectional and/or bidirectional DC/DC converters. For example, <FIG> illustrates a schematic diagram of a UPS <NUM> in which the DC/DC converter <NUM> may be implemented as one or more unidirectional DC/DC converters, one or more bidirectional DC/DC converters, a combination of the foregoing, and so forth. Accordingly, the principles of the disclosure are not limited to DAB converters nor to bidirectional converters. Similarly, although in some examples the first inverter stage including the inverter switching devices <NUM>-<NUM> may be controlled to switch at a low frequency (for example, a line frequency) and the second inverter stage including the inverter switching devices <NUM>, <NUM> may be controlled to switch at a high frequency, in other examples other modulation schemes may be implemented.

Acts of the process <NUM> may not be executed sequentially. For example, acts <NUM>, <NUM>, and <NUM> may all be executed repeatedly and substantially simultaneously until a determination is made that the positive half-cycle of the AC output waveform is complete (<NUM> YES). Similarly, acts <NUM>, <NUM>, and <NUM> may all be executed repeatedly and substantially simultaneously until a determination is made that the negative half-cycle of the AC output waveform is complete (<NUM> YES). Furthermore, in various examples acts <NUM> and <NUM> may not include actions affirmatively executed by the controller <NUM>, and may instead be provided for clarity of explanation.

In various examples, components may be added to or removed from the UPS <NUM>. In some examples, the snubber capacitor <NUM> may be implemented as illustrated. The snubber capacitor <NUM> may advantageously mitigate stray inductances. In other examples, the snubber capacitor <NUM> may be omitted and replaced with an open circuit. Removing the snubber capacitor <NUM> may advantageously reduce losses.

Although examples have been provided in which an inverter and a DC/DC converter are coupled together in a UPS, the principles of the disclosure are not limited to UPSs. For example, the inverter and DC/DC converter topologies and modulation schemes may be implemented in any of various other power systems, such as electric vehicle systems, mobile phone systems, microgrid systems, and so forth.

Claim 1:
A power system (<NUM>) comprising:
a power-system output (<NUM>) configured to be coupled to, and provide an output AC waveform to, one or more loads;
a positive DC bus (106a);
a negative DC bus (106b);
an inverter (<NUM>) coupled to the positive DC bus and to the negative DC bus, the inverter including an inverter output coupled to the power-system output (<NUM>), the inverter being implemented as a two-stage inverter according to an active neutral-point clamped, ANPC, topology, wherein a first stage of the inverter (<NUM>) comprises a set of inverter switching devices comprising an upper-most inverter switching device and a lower-most inverter switching device ; and
a DC/DC converter (<NUM>),
characterized in that the DC/DC converter comprises a first port connected to the inverter and a second port,
in that the upper-most inverter switching device (<NUM>) is coupled to the positive DC bus (106a) at a first connection and to a first terminal of said first port at a second connection, and
in that the lower-most inverter switching device (<NUM>) is coupled to a second terminal of said first port at a first connection and to the negative DC bus (106b) at a second connection.