Method for adjusting the frequency of a plurality of uninterruptible power supply units and corresponding uninterruptible power supply unit - Patents.com

Abstract

The present disclosure relates to a method for adjusting the frequency of a plurality of uninterruptible power supply units and corresponding uninterruptible power supply units. The method includes: for the control unit of each UPS unit, broadcasting an expected synchronization direction determined based on the frequency of the corresponding UPS unit and the frequency of a grid to other UPS units via a communication link; obtaining an expected synchronization direction of other UPS units via the communication link; determining a dominant synchronization direction based on the expected synchronization direction of each UPS unit; and adjusting the frequency of each UPS unit based on the dominant synchronization direction. According to the embodiment of the present disclosure, a simple, robust and reliable parallel UPS configuration can be realized.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Exemplary embodiments of the present disclosure relate generally to the field of uninterruptible power supplies, and more particularly, to a method for adjusting the frequency of multiple uninterruptible power supply units and a corresponding uninterruptible power supply. [Background technology]

[0002] An uninterruptible power supply (UPS) is an important electrical device that provides a stable power supply to electrical equipment. A UPS operates in two main modes: power regulation mode and island mode. When the input, which is the grid connected to the UPS, is stable, the UPS operates in power regulation mode and provides the desired power to the output, which is the load connected to the UPS. When the grid fails, the UPS operates in island mode and acts as a voltage source for the load and supplies power from the battery. The two modes can be switched by a switch included in the UPS. When the switch is closed, the UPS is in power regulation mode and controls the output voltage amplitude and frequency by regulating the power change between the UPS and the power source. When a power quality event occurs, the switch is opened and the UPS transitions to island mode. In this island mode, the load active power flows from the energy storage through the inverter, and the UPS controls the output voltage at a predetermined voltage amplitude and frequency.

[0003] Conventionally, a UPS may include multiple UPS units. When the grid voltage is restored and the UPS transitions from the island mode to the power conditioning mode, some inconsistencies will occur between the UPS units. For example, each UPS unit may make different decisions about whether to change mode from the island mode to the power conditioning mode based on the unit's local information, or each UPS unit may make their transition decision at different moments (i.e., different times of synchronization start). Such inconsistencies may cause problems and need to be addressed.

[0004] Therefore, it is necessary to achieve synchronization between multiple UPS units in a UPS. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY Exemplary embodiments of the present disclosure propose solutions that address at least problems and / or potential problems in the prior art. [Means for solving the problem]

[0006] An embodiment of the present disclosure relates to a method for adjusting the frequency of multiple UPS units, each having a controller, the method including: broadcasting, for the controller of each UPS unit, an expected synchronization direction determined based on the frequency of the corresponding UPS unit and a grid frequency to other UPS units via a communication link; obtaining expected synchronization directions of the other UPS units via the communication link; determining a primary synchronization direction based on the expected synchronization direction of each UPS unit; and adjusting the frequency of each UPS unit based on the primary synchronization direction.

[0007] According to the embodiments of the present disclosure, synchronization between UPS units can be achieved.

[0008] In some embodiments, a drift frequency is applied to the frequency of the UPS unit in response to determining that the phase angle difference between a corresponding UPS unit and the grid is within an angle limit band centered around 180 degrees.

[0009] In some embodiments, adjusting the frequency of each UPS unit includes, in response to determining that the frequency of the UPS unit is higher than the frequency of the grid, lowering the frequency of the UPS unit until it is equal to the frequency of the grid.

[0010] In some embodiments, adjusting the frequency of each UPS unit includes, in response to determining that the frequency of the UPS unit is lower than the frequency of the grid, increasing the frequency of the UPS unit until it is equal to the frequency of the grid.

[0011] In some embodiments, the range is selected from 5 to 15 degrees.

[0012] In some embodiments, the communication link is a communication bus.

[0013] An embodiment of the present disclosure relates to an uninterruptible power supply comprising: a switch disposed between a load and a power source configured to supply power to the load; a power management module having a primary energy storage; an inverter disposed between and coupled to the power management module and the load; and a controller coupled to the power management module, the inverter and the switch, the controller configured to: broadcast, for the controller of each UPS unit, an expected synchronization direction determined based on a frequency of the corresponding UPS unit and a frequency of a grid to other UPS units via a communication link; obtain, via the communication link, an expected synchronization direction of the other UPS units; determine a primary synchronization direction based on the expected synchronization direction of each UPS unit; and adjust the frequency of each UPS unit based on the primary synchronization direction.

[0014] In some embodiments, the controller is configured to apply a drift frequency to the frequency of the UPS unit in response to determining that a phase angle difference between a corresponding UPS unit and the grid is within an angle limit band centered around 180 degrees.

[0015] In some embodiments, the controller is further configured to, in response to determining that the frequency of the UPS unit is higher than the frequency of the grid, reduce the frequency of the UPS unit until it is equal to the frequency of the grid.

[0016] In some embodiments, the controller is further configured to increase the frequency of the UPS unit until it becomes equal to the frequency of the grid in response to determining that the frequency of the UPS unit is lower than the frequency of the grid.

[0017] In some embodiments, the range is 5 to 15 degrees.

[0018] In some embodiments, the communication link is a communication bus. [Brief description of the drawings]

[0019] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings, in which several embodiments of the present disclosure are illustrated by way of example and not by way of limitation. [Figure 1] FIG. 2 illustrates an example usage scenario of an uninterruptible power supply in accordance with an example embodiment of the present disclosure. [Diagram 2] FIG. 2 illustrates another usage scenario of an uninterruptible power supply in accordance with an exemplary embodiment of the present disclosure. [Diagram 3] FIG. 2 illustrates a method for adjusting the frequency of multiple UPS units according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The principles of the present disclosure will now be described with reference to various exemplary embodiments shown in the figures. It should be understood that the description of these embodiments is merely intended to enable those skilled in the art to better understand and further implement the exemplary embodiments disclosed herein, and is not intended to limit the scope of the present disclosure in any way. It should be noted that similar or identical reference symbols may be used in the drawings, where feasible, and similar or identical reference symbols may represent similar or identical functions. Those skilled in the art can easily recognize from the following description that alternative embodiments of the structures and methods described herein can be utilized without departing from the principles of the present disclosure described herein.

[0021] As used herein, the term "comprises" and variations thereof should be understood as open-ended terms meaning "including, but not limited to." The term "based on" should be understood as "based at least in part on." The terms "one embodiment" and "embodiment" should be understood as "at least one embodiment." The term "another embodiment" should be understood as "at least one other embodiment." The terms "first," "second," etc. may refer to the same or different objects. The following text may also include other explicit and implicit definitions. Unless otherwise indicated by context, definitions of terms are consistent throughout the description.

[0022] FIG. 1 illustrates an exemplary usage scenario of an uninterruptible power supply 100 according to an exemplary embodiment of the present disclosure. The scenario illustrated in FIG. 1 is referred to as a hard-parallel configuration. The uninterruptible power supply 100 according to the embodiment may be a medium-voltage uninterruptible power supply that is an impedance-isolated static converter type. It should be understood that this type of uninterruptible power supply 100 is merely an example, without implying any limitation to the scope of the present disclosure.

[0023] As shown in FIG. 1 , the uninterruptible power supply 100 is connected to a load 200 on a downstream side (also referred to as the “load side”) and to a power source 300 on an upstream side (also referred to as the “power supply side”). In this embodiment, the power source 300 is a grid supply providing a utility voltage. It should be understood that the power source 300 may be other types of power sources. The load 200 and the power source 300 are interconnected by a power bus 105 including a cable or a bus bar. Although the power bus 105 in this embodiment may be a part of a system installation for interconnecting the power source 300 and the load 200, the power bus 105 is considered as a part of the uninterruptible power supply 100. It should also be understood that the load 200 may include individual load units individually connected to the power bus 105. These load units together form the load 200.

[0024] As shown in FIG. 1, the dashed lines represent multiple UPS units 110 included in the uninterruptible power supply system 100. The UPS units 110 may be the same. It should be understood that the UPS units 110 may be slightly different from each other but together form the uninterruptible power supply system 100. Each UPS unit 110 is connected to the other UPS units 110 via a communication bus (not shown). The communication bus allows the UPS units 110 to share some information (e.g., the frequency or phase angle of each UPS unit 110) with the other UPS units 110. Thus, each UPS unit 110 knows the frequency or phase angle of the other UPS units 110.

[0025] The internal configuration of the UPS unit 110 will be described below. As shown in FIG. 1, the UPS unit 110 includes a switch 102 disposed in a power bus 105 between a power source 300 and a load 200. The UPS unit 110 further includes a power management module 109. The power management module 109 includes an energy storage unit for supplying power to the load 200. The UPS unit 110 may further include an inverter 104. The inverter 104 may be disposed between the power management module 109 and the load 200 and coupled to the power management module 109 and the load 200. In some embodiments, the uninterruptible power supply 100 may further include a plurality of coupling transformers 107-1, 107-2, 107-3, and 107-4 configured to perform voltage regulation as required.

[0026] In the illustrated embodiment, the UPS unit 110 also includes a controller 108. The controller 108 is configured to control the performance of the UPS unit 110. In other exemplary embodiments, the controller 108 may also be configured to monitor the power source for power quality events. The controller 108 is separate from the other components of the UPS unit 110. In an alternative embodiment, the inverter 104 may be provided integral with the controller 108.

[0027] As shown in FIG. 1 , the controller 108 may be connected to the switch 102, the inverter 104 via a communication connection 103. In the embodiment shown, the power management module 109 is also connected to the controller 108 via the communication connection 103. The communication connection 103 may be, for example, an industrially robust, low latency and / or long distance communication link. The communication connection 103 is provided as a communication bus to which all components of the UPS unit 110 are connected. In an alternative embodiment, all components of the UPS unit 110 are individually connected to the controller 108.

[0028] Overall, the uninterruptible power supply 100 comprising multiple UPS units 110 is configured to supply power to the load 200 when a power quality event occurs, for example, when the power source 300 fails. As used herein, a power quality event may refer to any event that may endanger the operation of the load 200, in particular a voltage drop, a complete failure of the power source 300, or a voltage disturbance of the power source 300. It should be understood that the uninterruptible power supply 100 described herein is for illustrative purposes only and does not imply any limitation to the scope of the present subject matter.

[0029] 2 illustrates another usage scenario of the uninterruptible power supply 100 according to an exemplary embodiment of the present disclosure. The scenario illustrated in FIG. 2 is referred to as a soft-parallel or ring bus configuration. FIG. 2 differs from FIG. 1 in that FIG. 2 shows only one UPS unit 110 in a common ring bus configuration, where multiple UPS units share a common grid connection and are all connected to a ring bus port 101.

[0030] FIG. 3 illustrates a method 30 for adjusting the frequency of multiple UPS units according to an exemplary embodiment of the present disclosure.

[0031] The controller 108 is configured to broadcast, in block 302, for each UPS unit 110 via the communication link an expected synchronization direction to the other UPS units. In some exemplary embodiments, the expected synchronization direction may indicate a forward or reverse direction. The expected synchronization direction may be determined according to the difference between the current frequency of the corresponding UPS unit 110 and the frequency of the grid 300. If the frequency of the UPS unit 110 is higher than the frequency of the grid 300, the phase of the UPS rotates slightly faster than the grid 300. If the UPS unit 110 wishes to synchronize its phase to the grid 300 and considers that its phase is lagging behind the phase of the grid 300, the UPS unit 110 may temporarily increase its frequency to "catch up" its phase to the grid 300. This is referred to as a forward direction. In other exemplary embodiments, the expected synchronization direction may indicate a positive frequency offset or a negative frequency offset.

[0032] Each UPS unit 110 can broadcast its expected synchronization direction to the other UPS units 110. The controller 108 is configured in block 304 to obtain the expected synchronization direction of the other UPS units 110 via the communication link.

[0033] The control unit 108 is configured to determine the primary synchronization direction based on the expected synchronization direction of each UPS unit 110 in block 306. For example, if the uninterruptible power supply 100 includes nine UPS units, and three of all nine UPS units 110 want to synchronize in the forward direction, while the other six UPS units 110 want to synchronize in the reverse direction, which means that the majority of the UPS units 110 want to synchronize in the reverse direction, then the reverse direction is selected as the primary synchronization direction. As a result, all nine UPS units 110 synchronize in the reverse direction according to the primary synchronization direction. In this case, these six UPS units 110 maintain their expected synchronization direction, but these three UPS units 110 must change their expected synchronization direction to maintain consistency with the majority of the UPS units 110. It should be understood that the number of UPS units 110 listed herein is merely an example, without implying any limitation to the scope of the present disclosure.

[0034] In block 308, the controller 108 is configured to adjust the frequency of each UPS unit 110 based on the primary synchronization direction so that the UPS units 110 can track the frequency of the grid 300. If the phase of the UPS unit 110 has already caught up with the grid 300, it is now synchronized, and the UPS unit 110 sets its frequency to be the same as the phase of the grid 300. In this way, the phase of the UPS unit 110 will not differ from the phase of the grid 300.

[0035] In some embodiments, if the controller 108 determines that the frequency of the UPS unit 110 is higher than the frequency of the grid 300, the frequency of the UPS unit 110 is lowered until it is the same as the frequency of the grid 300. If the controller 108 determines that the frequency of the UPS unit 110 is lower than the frequency of the grid 300, the frequency of the UPS unit 110 is increased until it is the same as the frequency of the grid 300.

[0036] According to the present disclosure, each UPS unit 110 shares its expected synchronization direction, and all UPS units 110 decide to go with the majority synchronization direction. With these arrangements, the frequency tracking of all UPS units 110 can be managed globally during the synchronization process to have a common frequency. Power imbalance between UPS units 110 can be minimized.

[0037] In another exemplary embodiment, during the synchronization process, the tracking of the phase angles of all UPS units 110 can be managed globally to have a common frequency, so that the phase angles of all UPS units 110 converge with the phase angle of the grid 300 with minimum circulating current.

[0038] If the parallel UPS units are 180 degrees out of the grid, it is not safe to synchronize them. This is because some of the UPS units will synchronize in the forward direction and some of the UPS units will synchronize in the reverse direction. Although it is reasonably safe to assume that UPS units sharing a common load bus will have output voltage vectors distributed in a small area, there will be variations due to different loads in the ring bus configuration and errors in the hard parallel configuration. This dispersion means that if the angle synchronization is achieved close to 180 degrees, some UPS units will choose clockwise rotation and other UPS units will choose reverse rotation to achieve synchronization. When this happens, the output voltage vectors of the different UPS units will diverge before converging again.

[0039] When the UPS unit 110 is 180 degrees out of phase with the grid, the UPS unit 110 may either reduce its frequency to reduce the angle difference between the UPS unit 110 and the grid 300 to zero, or increase its frequency to increase the angle difference to 360 degrees, which is equal to 0 degrees. Thus, uncertainty arises in this situation. In some embodiments, an angle limit band is proposed to address the ambiguity when there is approximately 180 degrees between the phase of the UPS unit 110 and the phase of the grid 300. This angle limit band is set close to 180 degrees. If the UPS unit controller determines that the UPS unit is close to 180 degrees out of phase with the grid (e.g., 170 degrees) and has entered the angle limit band, a drift frequency may be generated to help move the UPS unit away from the 180 degree point.

[0040] In some embodiments, the drift frequency is applied to the frequency of the UPS unit in response to determining that the phase angle difference between the corresponding UPS unit and the grid is within the angle limit band. In this way, the phase of the UPS unit 110 is far enough away from 180 degrees, and then the UPS unit 110 can decide to increase or decrease the phase. Therefore, how to synchronize is clear and does not cause ambiguity. Only when the phase of the UPS 110 is far enough away from 180 degrees, the control unit 108 decides how to synchronize.

[0041] In some embodiments, the angle limit band may be selected as a range centered on 180 degrees, and such range may be selected from 5 to 15 degrees. In another exemplary embodiment, the range may be a range of 10 degrees centered on 180 degrees (meaning an angle of +170 to -170 degrees). It should be understood that the angle values ​​described herein are merely examples, and the specific values ​​are not limited to the embodiments of the present disclosure.

[0042] The uninterruptible power supply 100 may further include a serial reactor 106 coupled between the switch 102 and the load 200 and configured to eliminate negative effects of disturbances such as harmonics and voltage imbalances by isolating the load from the power supply disturbances.

[0043] In some embodiments, the communication link may be a common communication bus. In some embodiments, the communication connection 103 may include a physical connection based on optical fiber. Alternatively, in some embodiments, the physical connection is based on a twisted pair connection. The communication connection 103 allows for a low latency, high speed, long distance communication connection.

[0044] In another aspect, the present disclosure relates to a corresponding uninterruptible power supply 100. It should be understood that the method described with reference to Fig. 3 may be used in conjunction with the control unit 108 of the uninterruptible power supply 100. For the sake of brevity, further details will not be repeated here.

[0045] Compared to conventional approaches, the controller of each UPS unit in the parallel UPS system according to the present disclosure is coupled with the controllers of other UPS units to coordinate control activities without supervision or system-level controller. The method described herein can be implemented in parallel configurations, especially in hard parallel and ring bus parallel configurations, which can expand the range of use. For example, UPS units 110 can be installed in parallel configurations over a larger distance.

[0046] Although the present subject matter has been described in language specific to structural features and / or methodological acts, it should be understood that the present subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A method for adjusting the frequency of a plurality of UPS units, each of which includes a controller, comprising: broadcasting, for each UPS unit's control unit, an expected synchronization direction determined based on the corresponding UPS unit's frequency and a grid frequency to other UPS units via a communication link; Obtaining an expected synchronization direction of another UPS unit via the communication link; determining a primary synchronization direction based on an expected synchronization direction of each UPS unit; adjusting a frequency of each UPS unit based on the primary synchronization direction; The method includes:

2. applying a drift frequency to the frequency of the UPS unit in response to determining that the phase angle difference between the corresponding UPS unit and the grid is within an angle limit band centered around 180 degrees. The method of claim 1.

3. Adjusting the frequency of each UPS unit includes, in response to determining that the frequency of the UPS unit is higher than the frequency of the grid, lowering the frequency of the UPS unit until it is equal to the frequency of the grid. The method of claim 1.

4. Adjusting the frequency of each UPS unit includes, in response to determining that the frequency of the UPS unit is lower than the frequency of the grid, increasing the frequency of the UPS unit until it is equal to the frequency of the grid. The method of claim 1.

5. The range is selected from 5 to 15 degrees. The method of claim 2.

6. The communication link is a communication bus. The method of claim 1.

7. a switch (102) disposed between a load (200) and a power source (300) configured to supply power to the load (200); a power management module (110) comprising a primary energy store (112); an inverter (104) disposed between and coupled to the power management module (110) and the load (200); a controller (108) coupled to the power management module (110), the inverter (104) and the switch (102); The control unit (108) broadcasting, for each UPS unit's control unit, an expected synchronization direction determined based on the corresponding UPS unit's frequency and a grid frequency to other UPS units via a communication link; Obtaining an expected synchronization direction of another UPS unit via the communication link; determining a primary synchronization direction based on the expected synchronization direction of each UPS unit; Configured to adjust the frequency of each UPS unit based on the primary synchronization direction Uninterruptible power supply device (100).

8. The control unit (108) is configured to apply a drift frequency to the frequency of the UPS unit in response to determining that the phase angle difference between the corresponding UPS unit and the grid is within an angle limit band included in a range centered on 180 degrees. The uninterruptible power supply (100) of claim 7.

9. The control unit (108) further In response to determining that the frequency of the UPS unit is higher than the frequency of the grid, the frequency of the UPS unit is lowered until it becomes equal to the frequency of the grid. The uninterruptible power supply (100) of claim 7.

10. The control unit (108) further In response to determining that the frequency of the UPS unit is lower than the frequency of the grid, the frequency of the UPS unit is increased until it becomes equal to the frequency of the grid. The uninterruptible power supply (100) of claim 7.

11. The range is 5 to 15 degrees. The uninterruptible power supply (100) of claim 8.

12. The communication link is a communication bus. The uninterruptible power supply (100) of claim 7.

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