Patent Description:
Robust power systems enable supplying power to one or more loads. Such power systems may include combinations of generation, transport, rectification, inversion and conversion of power to supply energy for electronic, optical, mechanical, and/or nuclear applications and loads. When implementing power systems and architectures, practical considerations include cost, size, reliability, and ease of implementation.

In at least some known power systems, one or more uninterruptible power supplies (UPSs) facilitate supplying power to a load. UPSs facilitate ensuring that power is continuously supplied to one or more critical loads, even when one or more components of a power system fail. Accordingly, UPSs provide a redundant power source. UPSs may be utilized in a number of applications (e.g., utility substations, industrial plants, marine systems, high security systems, hospitals, datacomm and telecomm centers, semiconductor manufacturing sites, nuclear power plants, etc.). Further, UPSs may be utilized in high, medium, or low power applications. For example, UPSs may be used in relatively small power systems (e.g., entertainment or consumer systems) or microsystems (e.g., a chip-based system).

However, if a UPS fails or is malfunctioning, the load may not receive sufficient quality power to operate. In at least some known systems, multiple UPSs are coupled to a load to provide additional power redundancy. If one UPS fails, the other UPSs provide power to the load. In these known systems, the transient caused by a UPS failure can reduce the power quality of the power supplied to the load. For example, in systems with a power distribution unit (PDU) isolation transformer coupled between the UPSs and the load, isolating a fault from a failed UPS may saturate the PDU isolation transformer, which affects the power quality of the power supplied to the load. <CIT> discloses a controller according to the preamble of claim <NUM>.

In a first aspect, there is provided a controller for identifying a fault location in an uninterruptible power supply (UPS) system according to claim <NUM>.

In a second aspect, there is provided a method for identifying a fault location within an uninterruptible power supply (UPS) system according to claim <NUM>.

Exemplary embodiments of an uninterruptible power supply (UPS) system are described herein. A plurality of UPSs are arranged in a ring bus configuration and configured to supply power to at least one load. The UPSs are each coupled to the ring bus through a respective choke to isolate the UPSs from each other. At least one static switch module is coupled between an associated UPS and the ring bus to enable power from other UPSs to bypass the respective choke when a fault condition occurs at the UPS. A controller is communicatively coupled to the UPSs to monitor and otherwise control the UPSs.

<FIG> is a schematic diagram of an exemplary UPS system <NUM> for providing redundant power to a load. In the exemplary embodiment, system <NUM> includes a first UPS <NUM>, a second UPS <NUM>, a third UPS <NUM>, a fourth UPS <NUM>, a first switchgear <NUM>, a second switchgear <NUM>, a third switchgear <NUM>, a fourth switchgear <NUM>, and a ring bus <NUM>. In other embodiments, system <NUM> includes additional, fewer, or alternative components, including those described elsewhere herein.

In the exemplary embodiment, first UPS <NUM> is coupled to first switchgear <NUM>. Similarly, second UPS <NUM> is coupled to second switchgear <NUM>, third UPS <NUM> is coupled to third switchgear <NUM>, and fourth UPS <NUM> is coupled to fourth switchgear <NUM>. Each UPS <NUM>, <NUM>, <NUM>, <NUM> is configured to generate a power output. In the exemplary embodiment, UPSs <NUM>, <NUM>, <NUM>, <NUM> are rated to generate <NUM> kilowatts (kW) of power. In some embodiments, UPSs <NUM>, <NUM>, <NUM>, <NUM> are configured to store power and convert the stored power for transmission. In one embodiment, system <NUM> further includes fuses (not shown in <FIG>) coupled to UPSs <NUM>, <NUM>, <NUM>, <NUM> that are configured to electrically disconnect UPSs <NUM>, <NUM>, <NUM>, <NUM> from system <NUM> when a fault condition occurs.

Switchgears <NUM>, <NUM>, <NUM>, <NUM> are configured to receive the power outputs from the respective UPSs <NUM>, <NUM>, <NUM>, <NUM> and transmit the outputs to ring bus <NUM> or loads <NUM>, <NUM>, <NUM>, <NUM>. In the exemplary embodiment, each load is coupled to a pair of switchgears through separate electrical connections (i.e., a "double corded configuration") to provide additional redundancy to each load. For example, load <NUM> is coupled between switchgears <NUM> and <NUM> to receive power from first UPS <NUM> and second UPS <NUM>. Power received at load <NUM> from third and fourth UPSs <NUM>, <NUM> is transmitted through ring bus <NUM> to switchgears <NUM>, <NUM>. In at least some embodiments, a power distribution unit (PDU) transformer is coupled between loads <NUM>, <NUM>, <NUM>, <NUM> and system <NUM>.

In the exemplary embodiment, switchgears <NUM>, <NUM>, <NUM>, <NUM> include a plurality of electrical switches <NUM> that are configured to selectively open and close in response to a control signal (e.g., from a controller (not shown in <FIG>)). Switches <NUM> may be, for example, circuit breakers. Switches <NUM> are positioned at various nodes within switchgears <NUM>, <NUM>, <NUM>, <NUM> to facilitate locating and isolating faults within system <NUM>. Switchgears <NUM>, <NUM>, <NUM>, <NUM> further include chokes <NUM>, <NUM>, <NUM>, <NUM>, respectively. Chokes <NUM>, <NUM>, <NUM>, <NUM> are coupled between UPSs <NUM>, <NUM>, <NUM>, <NUM> and ring bus <NUM>. Chokes <NUM>, <NUM>, <NUM>, <NUM> facilitate load sharing within system <NUM> through frequency droop, and to limit fault current in case of a fault occurring at ring bus <NUM>.

Ring bus <NUM> is configured to couple each UPS <NUM>, <NUM>, <NUM>, <NUM> together such that the UPSs are configured to limit fault current and to provide additional power redundancy in the event of a fault condition at a UPS. Ring bus <NUM> includes a plurality of ring bus switches <NUM>. In the exemplary embodiment, ring bus <NUM> is divided into data halls <NUM>. Each data hall <NUM> is associated with a pair of UPSs and a pair of dual corded loads. For example, one data hall <NUM> is associated with UPSs <NUM>, <NUM> and loads <NUM>, <NUM>. In the exemplary embodiment, ring bus <NUM> includes two data halls <NUM>. In other embodiments, ring bus <NUM> includes a different number of data halls <NUM>. In one embodiment, each data hall <NUM> is housed within a switchgear enclosure.

During a transient period after a faulted UPS is disconnected from system <NUM>, power from ring bus <NUM> passes through an associated choke. The associated choke creates a voltage drop by blocking a portion of the power provided by ring bus <NUM>, which causes the power quality at the PDU transformers and the loads coupled to the faulted UPS to be reduced. The associated voltage distortion may also cause saturation of the magnetic core of the PDU transformer, further reducing the power quality at the loads. Additionally, the choke may prevent sufficient current from passing to a fuse of the faulted UPS. With a limited fault current from ring bus <NUM>, the fuse remains intact and the faulted UPS remains connected to system <NUM>, which may cause a reduction in power quality at the load.

<FIG> is a partial schematic view of system <NUM> (shown in <FIG>). More specifically, <FIG> is a schematic view of first UPS <NUM>, first switchgear <NUM>, partial ring bus <NUM>, and a controller <NUM>.

In the exemplary embodiment, controller <NUM> is communicatively coupled to UPS <NUM>. Controller <NUM> is also communicatively coupled to UPSs <NUM>, <NUM>, <NUM> within system <NUM> (each shown in <FIG>). In other embodiments, a plurality of controllers may be used. In some embodiments, controller <NUM> is coupled to a substitute controller (not shown) that may be used in the event that controller <NUM> fails.

In the exemplary embodiment, controller <NUM> is implemented by a processor <NUM> communicatively coupled to a memory device <NUM> for executing instructions. In some embodiments, executable instructions are stored in memory device <NUM>. Alternatively, controller <NUM> may be implemented using any circuitry that enables controller <NUM> to control operation of UPS <NUM> as described herein. For example, in some embodiments, controller <NUM> may include a state machine that learns or is pre-programmed to determine information relevant to which loads require power. For example, controller <NUM> dynamically determines what power resources will be needed and at what performance level and environmental conditions (e.g., temperature, humidity, time of day, etc.) those power resources will need to operate. Controller <NUM> may perform dynamic monitoring to determine whether a given load is satisfied with the power delivered, and whether delivered power is free of harmonics, transients, etc. In some embodiments, dynamic monitoring includes tracking resource usage to determine how much current or voltage should be delivered. Controller <NUM> may also monitor and/or control rapidity (i.e., bandwidth) and inverter capability (e.g., overload, reactive power, active power) to facilitate ensuring reliability of system <NUM> and minimizing performance degradation of UPSs <NUM>.

Controller <NUM> may also include a state machine scheduler configured to selectively activate and deactivate power resources, set voltage and current levels, and/or take power saving actions (e.g., reducing current delivery). Controller <NUM> may also track characteristics (e.g., static allocation of power) of system <NUM> to determine whether one or more components of system <NUM> should be put on standby or whether power should be diverted.

In the exemplary embodiment, controller <NUM> performs one or more operations described herein by programming processor <NUM>. For example, processor <NUM> may be programmed by encoding an operation as one or more executable instructions and by providing the executable instructions in memory device <NUM>. Processor <NUM> may include one or more processing units (e.g., in a multi-core configuration). Further, processor <NUM> may be implemented using one or more heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, processor <NUM> may be a symmetric multi-processor system containing multiple processors of the same type. Further, processor <NUM> may be implemented using any suitable programmable circuit including one or more systems and microcontrollers, microprocessors, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), programmable logic circuits, field programmable gate arrays (FPGA), and any other circuit capable of executing the functions described herein. In the exemplary embodiment, processor <NUM> causes controller <NUM> to operate UPS <NUM>, as described herein.

Controller <NUM> is configured to transmit and receive data from UPS <NUM>. For example, controller <NUM> is configured to transmit data to UPS <NUM> indicating ring bus <NUM> is connected. In another example, controller <NUM> receives data from UPS <NUM> indicating a fault condition has occurred or maintenance is required. Controller <NUM> is also configured to transmit control signals to system <NUM>. For example, controller <NUM> is configured to adjust the magnitude, frequency, and/or phase of the power output generated by UPS <NUM>. In one embodiment, controller <NUM> monitors each UPS and adjusts the operation of each connected UPS to synchronize the power outputs of the UPSs. Power losses caused by mismatched power outputs may be reduced by synchronizing the power outputs. In embodiments with multiple controllers, the controllers are in communication to coordinate the operation of each UPS. In another embodiment, UPS <NUM> may directly control magnitude and frequency of the generated output power based on its own measurements. In one embodiment, UPS <NUM> may employ frequency droop control based on output active power and voltage magnitude droop based on output reactive power. Series choke <NUM> facilitates load sharing between the UPS modules, and the employed droop techniques facilitate isochronous operation of all UPSs connected to ring bus <NUM>.

Controller <NUM> is further configured to monitor the circuit within switchgear <NUM> to detect fault conditions and other abnormal conditions of system <NUM>. In one embodiment, controller <NUM> is communicatively coupled to a contactor <NUM> within switchgear <NUM>. In some embodiments, contactor <NUM> is replaced with a relay. When a current or voltage differential monitored by contactor <NUM> exceeds a predetermined threshold, controller <NUM> is configured to selectively open or close one or more switches <NUM>, switches <NUM>, and/or contactor <NUM> to electrically disconnect UPS <NUM> from system <NUM> and protect the loads.

<FIG> is a schematic view of an exemplary UPS system <NUM>. System <NUM> is substantially similar to system <NUM> (shown in <FIG>) and, in the absence of contrary representation, includes similar components. In the exemplary embodiment, system <NUM> includes a first UPS <NUM>, a second UPS <NUM>, a third UPS <NUM>, a first switchgear <NUM>, a second switchgear <NUM>, a third switchgear <NUM>, and a ring bus <NUM>. In other embodiments, system <NUM> includes additional, fewer, or alternative components, including those described elsewhere herein. For example, system <NUM> may include a fourth UPS (not shown in <FIG>). System <NUM> further includes controller <NUM> (shown in <FIG>) that is communicatively coupled to UPSs <NUM>, <NUM>, <NUM>.

Each UPS <NUM>, <NUM>, <NUM> includes a power storage device <NUM>, such as a battery or capacitor, an alternating current (AC) to direct current (DC) converter <NUM>, and a DC-to-AC inverter <NUM>. In other embodiments, UPSs <NUM>, <NUM>, <NUM> have a different configuration. Power storage device <NUM> is configured to store electrical energy and provide the stored energy to the loads. In the exemplary embodiment, power storage device <NUM> is coupled between converter <NUM> and inverter <NUM>. AC-to-DC converter <NUM> is coupled to an external power source (not shown), such as a utility grid, and is configured to convert AC power received from the external power source into DC power for power storage device <NUM>. Inverter <NUM> is configured to receive DC power from power storage device <NUM> and AC-to-DC converter <NUM> and convert the power to an AC power output for system <NUM>. In the exemplary embodiment, controller <NUM> is configured to control the operation of converter <NUM> and/or inverter <NUM> (e.g., adjusting switching frequencies, etc.) to adjust the operation of system <NUM> and the power supplied to the loads.

Each UPS <NUM>, <NUM>, <NUM> is coupled to a pair of PDU transformers and a pair of loads. In the exemplary embodiment, UPS <NUM> and UPS <NUM> are each coupled to a first PDU transformer <NUM>, a first load <NUM>, a second PDU transformer <NUM>, and a second load <NUM>. That is, loads <NUM>, <NUM> are coupled to system <NUM> in a dual-corded configuration (i.e., two UPSs are separately connected to each load to provide redundant power). UPS <NUM> is coupled to a third PDU transformer <NUM>, a third load <NUM>, a fourth PDU transformer <NUM>, and a fourth load <NUM>. In the exemplary embodiment, loads <NUM>, <NUM> are in a single-corded configuration (i.e., a single connection to system <NUM> to receive power). However, loads <NUM>, <NUM> may further be coupled to another UPS (not shown).

Switchgears <NUM>, <NUM>, <NUM> include chokes <NUM>, <NUM>, <NUM>, respectively. Switchgears <NUM>, <NUM>, <NUM> further include circuit breakers <NUM> that are configured to isolate faults within system <NUM> by selectively disconnecting a portion of system <NUM>. In some embodiments, circuit breakers <NUM> are monitored and controlled by controller <NUM>. For ring bus applications, chokes <NUM>, <NUM>, <NUM> are sized to sustain a bolted fault on ring bus <NUM> for a sufficient time to isolate the fault through the activation of the specific breakers <NUM> in system <NUM>. Further, for situations where a breaker <NUM> fails to open, additional time may be built-in to determine and execute an alternative fault isolation strategy. Accordingly, to facilitate increasing a duration of time where inverter <NUM> of an associated UPS <NUM>, <NUM>, or <NUM> can sustain a bolted fault on ring bus <NUM>, chokes <NUM>, <NUM>, <NUM> may be sized to operate inverter <NUM> in a linear mode under a short circuit on ring bus <NUM>.

To prevent limited fault current and reduced power quality at the loads during the transient period after a fault is detected at a UPS, system <NUM> includes static switch modules <NUM>, <NUM>, <NUM>. Static switch modules <NUM>, <NUM>, <NUM> are coupled between ring bus <NUM> and UPSs <NUM>, <NUM>, <NUM>, respectively. Static switch modules <NUM>, <NUM>, <NUM> may include, but are not limited to, thyristors and insulated gate bi-polar transistors (IGBTs). In other embodiments, static switch modules <NUM>, <NUM>, <NUM> are replaced with contactors, static transfer switches, and/or other relatively fast switching devices. In the exemplary embodiment, each static switch module <NUM>, <NUM>, <NUM> includes a pair of static switches. In other embodiments, a different number of static switch modules and/or static switches per module may be included. Although it is shown that static switch modules <NUM>, <NUM>, <NUM> are outside of switchgears <NUM>, <NUM>, <NUM>, it is to be understood that static switch modules <NUM>, <NUM>, <NUM> may be within switchgears <NUM>, <NUM>, <NUM> or UPSs <NUM>, <NUM>, <NUM>.

Static switch modules <NUM>, <NUM>, <NUM> are configured to selectively bypass chokes <NUM>, <NUM>, <NUM>. In particular, static switch modules <NUM>, <NUM>, <NUM> are configured to selectively bypass chokes <NUM>, <NUM>, <NUM> in response to a detected fault condition at an associated UPS. During normal operation of system <NUM> (i.e., no fault conditions have occurred), static switch modules <NUM>, <NUM>, <NUM> are open. Static switch modules <NUM>, <NUM>, <NUM> are closed in response to a fault condition detected at an associated UPS. Static switch modules <NUM>, <NUM>, <NUM> are configured to provide a low impedance path between the faulted UPS and ring bus <NUM>, thereby facilitating sufficient fault current to disconnect the faulted UPS and maintaining or improving power quality at the loads using the power provided through ring bus <NUM>. In the exemplary embodiment, the fault current (i.e., current delivered in response to a fault condition) provided by ring bus <NUM> through static switch modules <NUM>, <NUM>, <NUM> is configured to be sufficient to blow a fuse associated with the faulted UPS to disconnect the faulted UPS from system <NUM>. Using static switches enables relatively fast reaction times to a detected fault in comparison to circuit breakers <NUM> and other switching devices. In one example, an exemplary circuit breaker closes in approximately <NUM> milliseconds (ms) while an exemplary static switch closes in approximately <NUM>-<NUM>.

In the exemplary embodiment, controller <NUM> is communicatively coupled to static switch modules <NUM>, <NUM>, <NUM> to selectively open and close switches <NUM>, <NUM>, <NUM>. Controller <NUM> is configured to detect a fault condition, determine which (if any) UPS is associated with the fault condition, and close a corresponding static switch to facilitate fault current bypassing a choke. An exemplary detection and control method is described in detail further below.

In some embodiments, static switch modules <NUM>, <NUM>, and <NUM> may be used in a different power system that includes parallel inverters coupled together with a choke. That is, the systems and methods described herein are not limited to UPS systems or UPS systems with a ring bus. The UPS systems are for illustrative purposes only and are not intended to limit the systems and methods as described herein. In one example, a static switch module may be coupled to an inverter parallel to a choke such that the static switch module is configured to selectively bypass the choke.

<FIG> and <FIG> are exemplary schematic diagrams <NUM>, <NUM> of an exemplary UPS system, such system <NUM> (shown in <FIG>), during a fault condition at a UPS. In particular, diagram <NUM> is a one-wire diagram of the three-phase system, and diagram <NUM> is a simplified circuit showing only one of the phases, with ring <NUM> modeled as a single power source. In the exemplary embodiment, diagram <NUM> includes a faulted UPS <NUM>, a fuse <NUM>, a choke <NUM>, a static switch module <NUM>, a ring bus <NUM>, a PDU transformer <NUM>, and a load <NUM>. Ring bus <NUM> includes three UPSs <NUM> with respective chokes <NUM>. In the exemplary embodiment, UPSs <NUM> are assumed to be operating without any fault conditions. Diagram <NUM> includes a faulted UPS <NUM>, a fuse <NUM>, a ring bus <NUM>, a PDU transformer <NUM>, and a load <NUM>. Similar to ring bus <NUM>, ring bus <NUM> includes multiple UPSs, represented as a single power source <NUM> and a choke <NUM>. In other embodiments, the UPS systems in diagrams <NUM>, <NUM> may include fewer, additional, or alternative components, including those described elsewhere herein.

With respect to <FIG> and <FIG>, the UPSs are represented as AC power sources. A fault condition has occurred at faulted UPSs <NUM>, <NUM>. That is, UPSs <NUM>, <NUM> generate substantially no power or power different from the power generated during normal operation of UPSs <NUM>, <NUM>. For example, the power factor of the power may be reduced. In the exemplary embodiment, fuses <NUM>, <NUM> are configured to electrically disconnect UPSs <NUM>, <NUM> from ring bus <NUM>, <NUM> and loads <NUM>, <NUM> when fuses <NUM>, <NUM> receive a current that exceeds a predetermined current threshold. When the fault condition results in substantially no power generated by UPSs <NUM>, <NUM>, ring buses <NUM>, <NUM> are configured to provide a fault current that exceeds the current threshold to fuses <NUM>, <NUM>. Fuses <NUM>, <NUM> are melted by the fault current to electrically disconnect faulted UPSs <NUM>, <NUM>.

With respect to <FIG>, the fault current bypasses choke <NUM> through static switch module <NUM>. Static switch module <NUM> is configured to provide substantially no voltage or current drop. Accordingly, since the fault current bypasses the choke through the static switch, neither the choke nor the static switch are shown in <FIG>.

PDU transformers <NUM>, <NUM> are configured to distribute power to loads <NUM>, <NUM>. In the exemplary embodiment, PDU transformer <NUM> is a delta-wye transformer. Although a single load is shown in <FIG> and <FIG>, it is to be understood that multiple loads may be coupled to PDU transformers <NUM>, <NUM>. Power is provided to PDU transformer <NUM> from ring bus <NUM> through static switch module <NUM>. Similarly, power is provided to PDU transformer <NUM> from ring bus <NUM>. In addition to providing power to PDU transformer <NUM> without the voltage drop caused by choke <NUM>, static switch module <NUM> provides a low impedance path for the fault current towards faulted UPS <NUM>. With respect to diagram <NUM>, the fault current would be provided by power source <NUM>. Upon failure of UPS <NUM>, the voltage at its output terminal collapses. The resulting potential difference across choke <NUM> drives a relatively steep rise of the current over it to feed the fault at UPS <NUM>. Once the fault is electrically disconnected by melting fuse <NUM> using the fault current, the magnetic flux applied to choke <NUM> to generate the fault current is then balanced by a reverse-applied flux that drives the current down. As PDU transformer <NUM> is exposed to the resulting voltage, the balanced flux balance applied to choke <NUM> also yields a balanced flux on PDU transformer <NUM>. Therefore, with respect to diagram <NUM>, static switch module <NUM> is configured to facilitate maintaining flux balance on PDU transformer <NUM> in the event of an internal fault on UPS <NUM>.

Unlike static switch module <NUM>, static transfer switches (STS) that may be used in UPS systems are likely to cause transformer saturation when transferring between asynchronous or out-of-phase power sources. In particular, in an example embodiment in which an STS feeds a PDU transformer that includes a primary source connected to the output of a UPS and a secondary source fed by a utility or ring bus. The two sources are likely to exhibit phase shift, and an out-of-phase transfer between the two power sources to the PDU transformer would drive the transformer into saturation, compromising power quality to one or more critical loads. The transfer may be delayed to avoid saturation, but the resulting power quality may not meet the demand of the load.

<FIG> are simplified diagrams illustrating fault scenarios for an exemplary fault detection method to distinguish between UPS faults and a load fault that may be used by system <NUM> (shown in <FIG>). As described above, closing a static switch module associated with a faulted UPS causes the fault current from the ring bus to bypass a choke and blow a fuse of the faulted UPS. However, in the event of a fault at the load, closing the static switch module causes the ring bus to be connected to the fault. Accordingly, system <NUM> is configured to determine a location of a fault and react accordingly. Although <FIG> only illustrate four exemplary fault scenarios, the exemplary fault detection method may also be used to detect faults in other additional fault scenarios and determine a location of the faults.

With respect to <FIG> and <FIG>, controller <NUM> is configured to monitor electrical data at each UPS <NUM>, <NUM>, <NUM> to detect and locate a fault. In the exemplary method shown in <FIG>, electrical data associated with inverter <NUM> is monitored. Inverter <NUM> includes two parallel converter modules <NUM> that generate an AC power output, an output inductance <NUM>, and an output capacitor <NUM>. The AC power output is transmitted to an associated switchgear <NUM>, <NUM>, or <NUM> to be delivered to the load and ring bus. In other embodiments, inverter <NUM> includes a different number of converter modules <NUM> (including one). Multiple modules are driven by the same Pulse Width Modulation (PWM) signal generated by controller <NUM> based on voltage and current readings from only one of the converter modules <NUM>.

Controller <NUM> is configured to collect measured current data associated with one output capacitor <NUM> and calculate a derived current associated with the same output capacitor <NUM>. Based on the comparison of the measured current data and the derived current, controller <NUM> is configured to determine a fault location (if any) and perform appropriate response actions to isolate the fault. Controller <NUM> opens and closes static switch modules, circuit breakers, switches, and the like within system <NUM> to isolate the fault. For example, if a UPS has a fault condition, controller <NUM> is configured to close a respective static switch to facilitate transmitting sufficient fault current from the ring bus to the fuse to disconnect the fuse. In another example, if the load has a fault condition, controller <NUM> is configured to open a circuit breaker between the faulted load and the UPSs of system <NUM> to disconnect the faulted line from the system.

Controller <NUM> is configured to monitor an inverter bridge current IS, a load current ILoad, and an output capacitor voltage VC using one or more sensors (not shown). The sensors may be any type of sensor that is configured to collect, calculate, or otherwise derive current and/or voltage data. The data is collected periodically, continuously, and/or in response to a signal (e.g., a sensor alert, a user command, etc.). Controller <NUM> is configured to calculate a measured current IC as the difference between the inverter bridge current IS and the load current ILoad. Controller <NUM> is further configured to calculate a derived current ID using the output capacitor voltage VC and a predetermined capacitance C of the measured output capacitor <NUM> (ID = C * dVC/dt). In one embodiment, the predetermined capacitance C is a nominal or rated value of output capacitor <NUM>. Controller <NUM> compares the measured current IC and the derived current ID. If the difference between current values exceeds a predetermined threshold, then a failure within the UPS is causing at least a portion of the current from reaching the load. Using data collected from inverter <NUM> enables controller <NUM> to distinguish between faults at the UPS and faults at the load because a fault at the load does not cause the difference in the current values to exceed the threshold. As such, controller <NUM> is configured to control system <NUM> to isolate the fault based on the location of the fault.

For example, <FIG> is an exemplary diagram <NUM> of a first scenario in which the measured output capacitor <NUM> has shorted. The inverter bridge current IS, and the load current ILoad are drawn to ground or neutral through the faulted output capacitor <NUM>. The measured current IC is relatively greater than the derived current ID such that the difference exceeds the predetermined threshold. Accordingly, controller <NUM> identifies the fault and determines that the fault is located at the UPS. In response, controller <NUM> closes the static switch to isolate the fault from system <NUM>. Similar to <FIG> is an exemplary diagram <NUM> of a second scenario in which an unmeasured output capacitor <NUM> has shorted. In the illustrated embodiment, the unmeasured output capacitor <NUM> is the upper output capacitor <NUM>. The measured current IC is relatively greater than the derived current ID similar to the first scenario and therefore controller <NUM> detects the fault.

<FIG> is an exemplary diagram <NUM> of a third scenario in which a measured converter <NUM> has a failure while <FIG> is an exemplary diagram <NUM> of a fourth scenario in which an unmeasured converter <NUM> has a failure. In the third and fourth scenarios, a link capacitor (not shown) within the failed converter <NUM> collapses to substantially zero impedance. In the fourth scenario, similar to the first and second scenarios, the difference between the measured current IC and the derived current ID exceeds the predetermined threshold and controller <NUM> determines a fault at the UPS has occurred. However, in the third scenario, the measured current IC and the derived current ID are consistent with each other, and the location of the fault remains undetermined. In the exemplary embodiment, controller <NUM> is communicatively coupled to inverter <NUM>, and inverter <NUM> is configured to alert controller <NUM> when a link capacitor has collapsed. For example, in an exemplary embodiment, inverter <NUM> may be implemented as a Voltage Source Converter (VSC) with an associated DC-side capacitance. A fault on the DC-side capacitance (i.e., causing the impedance of the DC-side to collapse to substantially zero) causes a DC voltage associated with the DC-side capacitance to collapse, thereby enabling prompt fault detection by detecting the drop in the DC voltage. A converter fault driving a short-circuit on the DC-side yields the same effects and triggers the same detection.

<FIG> is a flow diagram of an exemplary method <NUM> for use with a UPS system, such as system <NUM> (shown in <FIG>). In the exemplary embodiment, method <NUM> is at least partially performed by a controller (e.g., controller <NUM>, shown in <FIG>). In other embodiments, method <NUM> includes additional, fewer, or alternative steps, including those described elsewhere herein.

In some embodiments, method <NUM> is performed continuously. In other embodiments, method <NUM> is performed periodically and/or in response to a control signal, such as a user command or a sensor alert signal. The controller receives <NUM> current data representative of an inverter current (e.g., inverter bridge current IS, shown in <FIG>) and a load current (e.g., load current ILoad, shown in <FIG>) for one or more UPSs in a ring bus configuration. An output capacitor is coupled to a node between the inverter current and the load current. The controller further calculates <NUM> a measured current based on the received current data. The controller determines <NUM> a voltage of the output capacitor and generates <NUM> a derived current based on the determined voltage and a predetermined capacitance (e.g., a nominal capacitance) of the output capacitor.

The controller further compares <NUM> the measured current and the derived current to identify a fault location and distinguish between a UPS fault condition and a load fault condition. Although referred to as a "load fault condition", it is to be understood that a load fault condition refers to a fault at any location external to the UPSs. In one embodiment, the controller calculates a difference between the measured and derived currents and compares the difference to a predetermined threshold. If the difference exceeds the threshold, the controller determines a UPS fault condition has occurred. If the difference is within the threshold, the controller may determine a load fault condition has occurred. In some embodiments, the controller may receive an alert signal from a UPS indicating a UPS fault condition has occurred irrespective of the comparison of the current difference and the threshold. The controller controls <NUM> a static switch based on the identified fault location. For example, if the fault location is at the UPS associated with the static switch, the controller controls <NUM> the static switch to close, thereby facilitating fault current from the ring bus to bypass a choke associated with the faulted UPS. In some embodiments, when a load fault condition is identified, the controller controls <NUM> the static switch to remain open. In addition, the controller controls one or more circuit breakers or switches of the UPS system to isolate the location of the fault condition from the UPSs. For example, if a load has a fault condition, the controller causes one or more circuit breakers between the UPSs and the load to disconnect.

Claim 1:
A controller (<NUM>) for identifying a fault location in an uninterruptible power supply (UPS) system (<NUM>, <NUM>) including a plurality of UPSs (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and a ring bus (<NUM>, <NUM>, <NUM>, <NUM>), each of the plurality of UPSs (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being connected to the ring bus (<NUM>, <NUM>, <NUM>, <NUM>) via a static switch (<NUM>, <NUM>, <NUM>, <NUM>) of a plurality of static switches (<NUM>, <NUM>, <NUM>, <NUM>), each UPS system (<NUM>, <NUM>) comprising an inverter (<NUM>) which includes a converter module (<NUM>), an output inductor (<NUM>) connected between an output of the converter module (<NUM>) and an output node of the inverter (<NUM>), and an output capacitor (<NUM>) connected between the output node of the inverter (<NUM>) and ground, the controller (<NUM>) communicatively coupled to a first static switch (<NUM>, <NUM>, <NUM>, <NUM>) of the plurality of static switches (<NUM>, <NUM>, <NUM>, <NUM>), the first static switch (<NUM>, <NUM>, <NUM>, <NUM>) coupled between a first UPS (<NUM>, <NUM>) of the plurality of UPSs (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the ring bus (<NUM>, <NUM>, <NUM>, <NUM>), the controller (<NUM>) operable to:
receive current data representative of an inverter current of the first UPS (<NUM>, <NUM>) measured between the output inductor (<NUM>) and the output node of the inverter (<NUM>) and a load current delivered by the first UPS (<NUM>, <NUM>) to the ring bus (<NUM>, <NUM>, <NUM>, <NUM>);
characterized in that the controller (<NUM>) is further operable to perform the following for the first UPS (<NUM>, <NUM>):
calculate a current difference between the inverter current and the load current;
determine a voltage of the output capacitor (<NUM>);
calculate a derived current based on the determined voltage and a predetermined capacitance of the output capacitor (<NUM>);
calculate a difference between the current difference and the derived current;
compare the difference to a predetermined threshold;
identify the fault location as being (i) at the first UPS (<NUM>, <NUM>) when the difference exceeds the predetermined threshold or (ii) at a location external to the first UPS (<NUM>, <NUM>) when the difference is within the predetermined threshold; and
control the first static switch (<NUM>, <NUM>, <NUM>, <NUM>) based on the identified fault location.