Flying battery with AC switch PFC front end for ups

A UPS comprising an input, an output, a battery circuit, a PFC stage, a switch configured to selectively couple an interface of the PFC stage to the input in an online mode and to the battery circuit in a backup mode, a positive DC bus, a negative DC bus, and a controller configured to operate, in the online mode, the PFC stage to provide DC power, derived from the input AC power, to the DC busses, to operate, in the backup mode, the PFC stage to provide DC power, derived from the backup DC power, to the DC busses, to operate, in a first stage of the backup mode, the battery circuit to couple a positive terminal of a DC source to the interface, and to operate, in a second stage of the backup mode, the battery circuit to couple a negative terminal of the DC source to the interface.

BACKGROUND

1. Field of Invention

The present invention relates generally to uninterruptible power supplies (UPS).

2. Discussion of Related Art

The use of power devices, such as uninterruptible power supplies (UPS), to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems and other data processing systems, is known. Known uninterruptible power supplies include on-line UPS's, off-line UPS's, line interactive UPS's as well as others. On-line UPS's provide conditioned AC power as well as back-up AC power upon interruption of a primary source of AC power. Off-line UPS's typically do not provide conditioning of input AC power, but do provide back-up AC power upon interruption of the primary AC power source. Line interactive UPS's are similar to off-line UPS's in that they switch to battery power when a blackout occurs but also typically include a multi-tap transformer for regulating the output voltage provided by the UPS.

SUMMARY

At least one aspect of the invention is directed to an Uninterruptible Power Supply (UPS) comprising an input configured to be coupled to an AC power source and to receive input AC power, an output configured to provide output power to a load, a battery circuit configured to be coupled to a DC source and to receive backup DC power, a Power Factor Correction (PFC) stage including an interface, an input switch configured to selectively coupled the interface of the PFC stage to the input in an online mode of operation and to the battery circuit in a backup mode of operation, a positive DC bus coupled to the PFC stage, a negative DC bus coupled to the PFC stage, and a controller coupled to the battery circuit and the PFC stage, the controller configured to operate, in the online mode of operation, the PFC stage to provide DC power, derived from the input AC power, to the positive DC bus and the negative DC bus, to operate, in the backup mode of operation, the PFC stage to provide DC power, derived from the backup DC power, to the positive DC bus and the negative DC bus, to operate, in a first stage of the backup mode of operation, the battery circuit to couple a positive terminal of the DC source to the interface of the PFC stage, and to operate, in a second stage of the backup mode of operation, the battery circuit to couple a negative terminal of the DC source to the interface of the PFC stage.

According to one embodiment, the UPS further comprises a neutral line, and the battery circuit comprises a first switch configured to be coupled between the input switch and the negative terminal of the DC source, a second switch configured to be coupled between the negative terminal of the DC source and the neutral line, a third switch configured to be coupled between the input switch and the positive terminal of the DC source, and a fourth switch configured to be coupled between the positive terminal of the DC source and the neutral line. In one embodiment, in operating the battery circuit to couple the positive terminal of the DC source to the interface of the PFC stage, the controller is further configured to operate the third switch to couple the positive terminal to the interface of the PFC stage via the input switch and to operate the second switch to couple the negative terminal to the neutral line.

According to another embodiment, in operating the battery circuit to couple the negative terminal of the DC source to the interface of the PFC stage, the controller is further configured to operate the first switch to couple the negative terminal to the interface of the PFC stage via the input switch and to operate the fourth switch to couple the positive terminal to the neutral line. In one embodiment, the PFC stage comprises an inductor coupled to the interface, a plurality of switches coupled to the inductor, a first bus capacitor coupled to the positive DC bus, and a second bus capacitor coupled to the negative DC bus. In another embodiment, in operating the PFC stage to provide DC power, derived from the backup DC power, to the positive DC bus and the negative DC bus, the controller is further configured to operate the plurality of switches, in the first stage of the backup mode of operation, to generate a positive DC voltage on the positive DC bus.

According to one embodiment, in operating the PFC stage to provide DC power, derived from the backup DC power, to the positive DC bus and the negative DC bus, the controller is further configured to operate the plurality of switches, in the second stage of the backup mode of operation, to generate a negative DC voltage on the negative DC bus. In one embodiment, the plurality of switches includes a fifth switch coupled to the inductor, a sixth switch coupled between the fifth switch and the neutral line, a seventh switch coupled between the inductor and the positive DC bus, and an eighth switch coupled between the inductor and the negative DC bus. In another embodiment, in operating the plurality of switches, in the first stage of the backup mode of operation, to generate the positive DC voltage on the positive DC bus, the controller is further configured to operate the fifth switch, the sixth switch, and the seventh switch as a boost converter to generate the positive DC voltage.

According to another embodiment, in operating the plurality of switches, in the second stage of the backup mode of operation, to generate the negative DC voltage on the negative DC bus, the controller is further configured to operate the fifth switch, the sixth switch, and the eighth switch as a boost converter to generate the negative DC voltage. In one embodiment, the UPS further comprises an inverter coupled between the DC busses and the output and configured to provide an output AC voltage waveform derived from at least one of the input AC power and the backup DC power, wherein the controller is further configured to synchronize generating the positive DC voltage on the positive DC bus with a positive half cycle of the output AC voltage waveform, and wherein the controller is further configured to synchronize generating the negative DC voltage on the negative DC bus with a negative half cycle of the output AC voltage waveform. In one embodiment, the PFC stage comprises a Vienna rectifier.

Another aspect of the invention is directed to a method for operating a UPS comprising an input configured to be coupled to an AC power source, an output configured to provide output power to a load, a battery circuit, a PFC stage, a positive DC bus, and a negative DC bus, wherein the method comprises receiving input AC power at the input from the AC power source, receiving backup DC power at the battery circuit from the DC power source, operating the UPS in an online mode of operation in response to a determination that the input AC power is greater than an input power threshold, operating the UPS in a backup mode of operation in response to a determination that the input AC power is less than the input power threshold, selectively coupling the input to an interface of the PFC stage in the online mode of operation, selectively coupling the battery circuit to the interface of the PFC stage in the backup mode of operation, converting, in the online mode of operation with the PFC stage, the input AC power into DC power provided to the positive and negative DC busses, converting, in the backup mode of operation with the PFC stage, the backup DC power into the DC power provided to the positive and negative DC busses, coupling, with the battery circuit in a first stage of the backup mode of operation, a positive terminal of the DC power source to the interface of the PFC stage, and coupling, with the battery circuit in a second stage of the backup mode of operation, a negative terminal of the DC power source to the interface of the PFC stage.

According to one embodiment, coupling the positive terminal of the DC power source to the interface of the PFC stage in the first stage includes operating a first switch to couple the positive terminal to the interface of the PFC stage, and operating a second switch to couple the negative terminal to a neutral line. In one embodiment, coupling the positive terminal of the DC power source to the interface of the PFC stage in the second stage includes operating a third switch to couple the negative terminal to the interface of the PFC stage, and operating a fourth switch to couple the positive terminal to a neutral line. In another embodiment, converting, in the backup mode of operation with the PFC stage, the backup DC power into the DC power provided to the positive and negative DC busses includes generating, during the first stage of the backup mode of operation, a positive DC voltage on the positive DC bus, and generating, during the second stage of the backup mode of operation, a negative DC voltage on the negative DC bus.

According to another embodiment, generating the positive DC voltage on the positive DC bus includes operating a plurality of switches in the PFC stage as a boost converter to generate the positive DC voltage. In one embodiment, generating the negative DC voltage on the negative DC bus includes operating the plurality of switches in the PFC stage as a boost converter to generate the negative DC voltage. In another embodiment, the UPS further comprises an inverter configured to provide an output AC voltage waveform derived from at least one of the input AC power and the backup DC power, and the method further comprises synchronizing generating the positive DC voltage on the positive DC bus with a positive half cycle of the output AC voltage waveform, and synchronizing generating the negative DC voltage on the negative DC bus with a negative half cycle of the output AC voltage waveform.

At least one aspect of the invention is directed to an Uninterruptible Power Supply (UPS) comprising an input configured to be coupled to an AC power source and to receive input AC power, an output configured to provide output power to a load, a positive DC bus, a negative DC bus, a PFC stage coupled to the positive DC bus and the negative DC bus and configured to convert the input AC power into regulated DC power provided to the positive DC bus and the negative DC bus, and means for selectively coupling the PFC stage to one of the input and a DC source and for operating the PFC stage to convert backup DC power from the battery into the regulated DC power provided to the positive DC bus and the negative DC bus.

DETAILED DESCRIPTION

As discussed above, power devices, such as uninterruptible power supplies (UPS), are oftentimes used to provide regulated, uninterrupted power to sensitive and/or critical loads. A conventional online UPS rectifies input AC power provided by an electric utility using a Power Factor Correction circuit (PFC) to provide DC power to at least one DC bus. The rectified DC power on the DC buses is typically used to charge a battery while mains power is available. In the absence of mains power, the battery discharges and provides DC power to the DC buses. From the DC power on the DC buses, an inverter generates an AC output voltage that is provided to a load. Since the DC bus is powered either by mains or the battery, the output power of the UPS is uninterrupted if the mains fails and the battery is sufficiently charged. Typical online UPS's may also operate in a bypass mode where unconditioned power with basic protection is provided directly from an AC power source to a load via a bypass line.

A UPS with a relatively high power rating typically includes a battery with a relatively high voltage level. The relatively high voltage level of the battery in a high-power UPS may make it practical to use a non-isolated boost converter to convert the battery voltage to a level appropriate to power the inverter stage. This is because a boost converter generally has a high efficiency when the input voltage of the boost converter is close to (e.g., only slightly lower then) the target regulated output voltage. For example, in some conventional high-power UPS systems, the front-end PFC stage of the UPS is reused as a boost converter to convert DC power from the battery to regulated DC power provided to the inverter during on-battery mode.

In at least one embodiment, a more efficient PFC converter front-end circuit is described herein that can be reused as a boost converter during on-battery mode (i.e., backup mode) to convert DC power from a battery to regulated DC power provided to an inverter of a UPS.

FIG. 1is a block diagram of an online UPS100according to one aspect of the present invention. The UPS100includes an input102, a converter104, a positive DC bus106, a negative DC bus107, an inverter108, an output110, and a controller114. The input102is coupled to the converter104. The positive DC bus106and the negative DC bus107are coupled between the converter104and the inverter108. The output110is coupled to the inverter108. The controller114is coupled to the input102, the output110, the converter104, the positive DC bus106, the negative DC bus107, and the inverter108. The converter104is also configured to be coupled to a battery112.

The input102is configured to be coupled to an AC mains power source and to receive input AC power having an input voltage level. The controller114monitors the input AC power received by the input102and is configured to operate the UPS100in different modes of operation based on the status of the input AC power received by the input102. When AC power provided to the input102is acceptable (i.e., above an input power threshold), the controller114operates the UPS100in an online mode of operation. In the online mode of operation, AC power from the input102is provided to the converter104. According to one embodiment, the converter104is a Power Factor Correction converter104; however, in other embodiments, other types of converters may be utilized.

The controller114operates the converter104to convert the AC power into DC power and provide the DC power to the positive DC bus106and the negative DC bus107. In one embodiment, DC power is also provided from the converter104to the battery112to charge the battery112. In another embodiment, DC power from the positive DC bus106and the negative DC bus107is provided to the battery112via a DC/DC converter to charge the battery112. In the online mode of operation, the inverter108receives DC power from the positive DC bus106and the negative DC bus107, and the controller114operates the inverter108to convert the DC power into regulated AC power and provide regulated AC power to a load coupled to the output110.

When AC power provided to the input102is not acceptable (i.e., below an input power threshold), the controller114operates the UPS100in a backup mode of operation. In the backup mode of operation, DC power from the battery112is regulated (e.g., by the converter104) and provided to the positive DC bus106and the negative DC bus107. The inverter108receives the DC power from the positive DC bus106and the negative DC bus107, and the controller114operates the inverter108to convert the DC power into regulated AC power and provide the regulated AC power to the output110.

FIG. 2is a schematic diagram illustrating one embodiment of the converter104. The converter104includes an input line202, a neutral line204, an input switch206, a battery circuit208, and a PFC stage209. The PFC stage209includes an interface203, an inductor210, a first switch (Q1)212, a second switch (Q2)214, a third switch (Q3)216, a fourth switch (Q4)218, a first bus capacitor220, and a second bus capacitor222. The battery circuit208includes a fifth switch (Q5)226, a sixth switch (Q6)228, a seventh switch (Q7)230, and an eight switch (Q8)232. In one embodiment, the switches (Q1-Q8)212-232are Gallium Nitride (GaN) Field-Effect Transistors; however, in other embodiments, different types of switches or transistors can be utilized. For example, in one embodiment, the switches (Q1-Q8)212-232are Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFET). In another embodiment, for switches Q5-Q8226-232, thyristors can be used. In at least one embodiment where the switches (Q1-Q8)212-232are GaN FETs and/or MOSFETs, each switch (Q1-Q8)212-232includes a built-in body diode coupled between the drain and the source. The body diodes227of switches Q5-Q8226-232are shown inFIG. 2, while the body diodes of switches Q1-Q4212-218are not shown for illustrative purposes.

The input line202and the neutral line204are configured to be coupled to an input power source (e.g., mains) via the input102. The neutral line204is coupled to ground224. The input switch206is configurable to selectively couple either the input line202or the battery circuit208to the interface203. The interface203is coupled to a first end of the inductor210. The second end of the inductor210is coupled to the drain of the first switch (Q1)212. The source of the first switch (Q1)212is coupled to the source of the second switch (Q2)214. The drain of the second switch (Q2)214is coupled to the neutral line204. The second end of the inductor210is also coupled to the source of the third switch (Q3)216and the drain of the fourth switch (Q4)218. The drain of the third switch (Q3)216is coupled to the positive DC bus106. The source of the fourth switch (Q4)218is coupled to the negative DC bus107. The first bus capacitor220is coupled between the positive DC bus106and the neutral line204. The second bus capacitor222is coupled between the negative DC bus107and the neutral line204.

The drain of the fifth switch (Q5)226and the source of the seventh switch (Q7)230are coupled to the input switch206. The source of the fifth switch (Q5)226is configured to be coupled to a negative terminal111of the battery112. The drain of the seventh switch (Q7)230is configured to be coupled to a positive terminal113of the battery112. The source of the sixth switch (Q6)228is configured to be coupled to the negative terminal111of the battery112. The drain of the eight switch (Q8)232is configured to be coupled to the positive terminal113of the battery112. The drain of the sixth switch (Q6)228and the source of the eighth switch (Q8) are coupled to the neutral line204. The controller114is coupled to the gate of each switch (Q1-Q8)212-232and the input switch206and is configured to transmit control signals to (i.e., control operation of) each switch (Q1-Q8)212-232and the input switch206).

As described above, the controller114monitors the input AC power received by the input102and is configured to operate the UPS100in different modes of operation based on the status of the input AC power received by the input102. When input AC power provided to the input102is acceptable (i.e., above an input power threshold), the controller114operates the UPS100in the online mode of operation. In the online mode of operation, the controller114operates the input switch206to couple the input line202to the inductor210via the interface203. When the input line202is coupled to the inductor210, the controller114operates the first switch (Q1)212, second switch (Q2)214, third switch (Q3)216, and fourth switch (Q4)218, in conjunction with the inductor210and the bus capacitors220,222, to generate a positive output DC voltage on the positive DC bus106and a negative output DC voltage on the negative DC bus107. In at least one embodiment, the controller114also operates the first switch (Q1)212, second switch (Q2)214, third switch (Q3)216, and fourth switch (Q4)218to provide Power Factor Correction (PFC).

When AC power provided to the input102is not acceptable (i.e., below an input power threshold), the controller114operates the UPS100in a backup mode of operation. In the backup mode of operation, the converter104is operated in multiple stages. For example,FIG. 3is a schematic diagram of a first stage of the backup mode of operation where a positive DC voltage is generated on the positive DC bus106, andFIG. 4is a schematic diagram of a second stage of the backup mode of operation where a negative DC voltage is generated on the negative DC bus107.

During the first stage of the backup mode of operation, for example shown inFIG. 3, the controller114operates the input switch206to couple the battery circuit208to the inductor210via the interface203. Also during the first stage of the backup mode of operation, the controller114operates the converter104to couple the positive terminal113of the battery112to the inductor210and the negative terminal111of the battery112to the neutral line204. For example, in at least one embodiment, the controller114operates the sixth switch (Q6)228to close, coupling the positive terminal113to the inductor210(via the input switch206and the interface203), and the seventh switch (Q7)230to close, coupling the negative terminal111to the neutral line204. Closed switches Q6228and Q7230are shown inFIG. 3as resulting direct connections.

In the first stage of the backup mode of operation when the sixth switch (Q6)228and the seventh switch (Q7)230are closed, the body diodes227of the fifth switch (Q5)226and the eighth switch (Q8)232are reverse biased and a current path302, shown inFIG. 3, is generated. The controller114operates the first switch (Q1)212, the second switch (Q2)214, and the third switch (Q3)216as a boost converter to charge the bus capacitor220coupled to the positive DC bus106(i.e., generate a positive DC voltage on the positive DC bus106). More specifically, the controller114alternates switching of the first switch (Q1)212, the second switch (Q2)214, and the third switch (Q3)216to generate the desired positive voltage level on the positive DC bus106. For example, when the first switch (Q1)212and the second switch (Q2)214are closed, the current path302passes from the inductor210to the neutral line204, via the first switch (Q1)212, and the second switch (Q2)214, energy is stored in the inductor210, and the current through the inductor210increases.

When the first switch (Q1)212and the second switch214are subsequently opened, a resulting current path from the inductor210to the positive DC bus106, via the body diode of the third switch (Q3),216is generated. The third switch (Q3)216can subsequently be operated to close by the controller114. By operating the switches as described above, the desired positive DC voltage level can be generated on the positive DC bus106.

During the second stage of the backup mode of operation, for example shown inFIG. 4, the controller114operates the input switch206to couple the battery circuit208to the inductor210via the interface203. Also during the second stage of the backup mode of operation, the controller114operates the converter104to couple the negative terminal111of the battery112to the inductor210and the positive terminal113of the battery112to the neutral line204. For example, in at least one embodiment, the controller114operates the fifth switch (Q5)226to close, coupling the negative terminal111to the inductor210(via the input switch206and the interface203), and the eighth switch (Q8)233to close, coupling the positive terminal113to the neutral line204. Closed switches Q5226and Q8232are shown inFIG. 4as resulting direct connections.

In the second stage of the backup mode of operation when the fifth switch (Q5)226and the eighth switch (Q8)232are closed, the body diodes227of the sixth switch (Q6)228and the seventh switch (Q7)230are reverse biased and a current path402, shown inFIG. 4, is generated. The controller114operates the first switch (Q1)212, the second switch (Q2)214, and the fourth switch (Q4)218as a boost converter to charge the second bus capacitor222coupled to the negative DC bus107(i.e., generate a negative DC voltage on the positive DC bus107). More specifically, the controller114alternates switching of the first switch (Q1)212, the second switch (Q2)214, and the fourth switch (Q4)218to generate the desired negative voltage level on the negative DC bus107. For example, when the first switch (Q1)212and the second switch (Q2)214are closed, the current path402passes from the neutral line204to the inductor210, via the second switch (Q2)214and the first switch (Q1)212, energy is stored in the inductor210, and current through the inductor210increases (in a direction opposite to that during the first stage of the backup mode of operation).

When the first switch (Q1)212and the second switch214are subsequently opened, a resulting current path from the negative DC bus107to the inductor210, via the body diode of the fourth switch (Q4)218, is generated. The fourth switch (Q4)218can subsequently be operated to close by the controller114. By operating the switches as described above, the desired negative DC voltage level can be generated on the negative DC bus107.

As described above, in the backup mode of operation, the converter104generates a positive DC voltage on the positive DC bus106(during the first stage of the backup mode of operation) and a negative DC voltage no the negative DC bus107(during the second stage of the backup mode of operation). In at least one embodiment, the controller114synchronizes the operation of the converter104in the backup mode of operation with the operation of the inverter108coupled to the DC busses106,107. For example, the controller114can synchronize the first stage of the backup mode of operation (i.e., when the positive terminal113of the battery112is coupled to the inductor210and the converter operates to generate a positive DC voltage on the positive DC bus106) with a positive half cycle of an output waveform provided by the inverter108to the output110. The controller114can further synchronize the second stage of the backup mode of operation (i.e., when the negative terminal113of the battery112is coupled to the inductor210and the converter operates to generate a negative DC voltage on the negative DC bus106) with a negative half cycle of the output waveform provided by the inverter108to the output110.

As discussed above, the controller114is configured to monitor and control operation of the UPS100. Using data stored in associated memory, the controller114is operable to execute one or more instructions that may result in the manipulation of one or more switches' conductive states. In some examples, the controller114can include one or more processors or other types of controllers. The controller114may perform a portion of the functions discussed herein on a processor, and perform another portion using an Application-Specific Integrated Circuit (ASIC) tailored to perform particular operations. Examples in accordance with the present invention may perform the operations described herein using many specific combinations of hardware and software and the invention is not limited to any particular combination of hardware and software components.

As described above, the PFC converter104is utilized in a single-phase UPS100. However, in other embodiments, the PFC converter104can be utilized with any other type of single phase online UPS with positive and negative DC busses. For example, in one embodiment, the PFC converter104is utilized in a 120V (RMS value) UPS system with a 120V (nominal) battery. In such a system, the DC voltage level on the DC busses is regulated to be around 200V. In another embodiment, the PFC converter104is utilized in a 230V (RMS value) UPS system with a 192V (nominal) battery. In such a system, the DC voltage level on the DC busses is regulated to be around 400V.

In at least one embodiment, the converter can also be utilized in a higher power UPS with three phase inputs. For example,FIG. 5is a schematic diagram of a converter500utilized in a three phase UPS.

As shown inFIG. 5, the converter500includes multiple inputs502a-c(e.g., each configured to be coupled to one phase of a three-phase power source), a battery circuit504(e.g., such as the battery circuit208shown inFIG. 2), and a Vienna rectifier506. An input switch503a-cis configured to selectively couple the Vienna rectifier506to either a corresponding input502a-cor the battery circuit504. In at least one embodiment, the Vienna rectifier506includes Silicon Carbide (SiC) diodes508and MOSFETs510; however, in other embodiments, the Vienna rectifier506is configured differently.

The converter500shown inFIG. 5is operated in substantially the same way as the converter103described above with respect toFIGS. 2-4, except that it generates the regulated DC output from all three phase inputs, rather than one single phase input.

As described above, during the backup mode of operation (i.e., the on-battery mode of operation) the PFC converter can be reused in a UPS to convert DC power from the battery112to regulated DC power. The converter described above can be operated with relatively low losses/high efficiency.

According to at least one embodiment, since switches Q5-Q8226-232operate at line frequency and only switch the battery voltage, lower voltage switches (e.g., lower voltage MOSFETs) can be utilized as switches Q5-Q8226-232. In one embodiment, the switches (Q1-Q8)212-232are GaN FETs and/or Metal-Oxide-Semiconductor Field-Effect Transistors; however, in other embodiments, different types of switches or transistors can be utilized.

In one embodiment, the third switch (Q3)216and the fourth switch (Q4)218are switches or transistors; however, in at least on embodiment, the third switch (Q3)216and the fourth switch (Q4)218can be replaced by diodes.

As described above, the battery circuit208is coupled to a dual DC bus PFC stage with AC switches (e.g., as shown inFIG. 2); however, in other embodiments, the battery circuit208can be coupled to a different type of PFC stage.

According to one embodiment, the battery circuit (e.g., shown inFIG. 2) includes a fuse in series with each switch Q5-Q8226-232in case of switch failure.