Network construction type UPS (Uninterrupted Power Supply) and control method thereof

Abstract

The invention discloses a network construction type UPS and a control method thereof, the UPS comprises a static bypass branch and an auxiliary power supply branch with an inverter, commercial power is input into the static bypass branch to supply power to a load, rectification input flows into the load through the auxiliary power supply branch, the static bypass branch and the auxiliary power supply branch form voltage source parallel connection, and the static bypass branch and the auxiliary power supply branch are connected in parallel. The auxiliary power supply branch is connected in series with a charging circuit and / or a discharging circuit, and at least one of the charging circuit and the discharging circuit is an isolated circuit; the system has the advantage that uninterruptible power supply in a real sense is realized.

Description

Technical Field

[0001] The present invention relates to the field of uninterruptible power supply, and particularly to a grid-forming UPS and its control method. Background Art

[0002] With the development of new energy and artificial intelligence technologies, the market demand for uninterruptible power supplies (UPS) is increasing. As Figure 1 shown, currently, a traditional UPS generally consists of a maintenance bypass branch with a maintenance bypass switch 1, a static bypass branch with a bypass static switch 3, a rectifier branch with a rectifier 4, a battery branch with a boost voltage, and an inverter branch with an inverter 7. Figure 1 In [the figure], 1 is the maintenance bypass switch, 2 is the load, 3 is the bypass static switch, 4 is the rectifier, 5 is the battery, 7 is the inverter, 8 is the rectifier switch, 11 is the inverter switch, 12 is the output switch, 14 is the boost circuit, and 15 is the battery switch. The existing UPS control strategy is that when the mains power fails and there is no power input from the bypass, the inverter branch is put into operation to maintain the power supply to the load. However, under the existing technical conditions, it takes time to detect the mains power failure, and the inverter branch does not switch seamlessly. In fact, the load will still have a short period of no input power supply state.

[0003] The power supply system for low-voltage distribution equipment to prevent power interruption during power fluctuations disclosed in Chinese Patent Publication No. CN116599030A includes a municipal power grid. A bypass maintenance switch is electrically connected to the municipal power grid, and a load system is electrically connected to the bypass maintenance switch; a rectifier module is electrically connected to the municipal power grid, a step-down voltage module is electrically connected to the rectifier module, a battery pack module is electrically connected to the step-down voltage module, an inverter module is electrically connected to the battery pack module, and a step-up voltage module is electrically connected to the inverter module. Then, the load system is powered through a static switch module. The on / off control of the power supply process is realized through the bypass maintenance switch, and the UPS power supply is composed of a rectifier module, a battery pack module, an inverter module, and a static switch module, that is, the UPS can output voltage when there is an external power failure. That is to say, this patent application also detects the mains power, and then the inverter branch is put into use, so that the load will have a short period of no input power supply state. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that when there is a mains power failure in the existing uninterruptible power supply, the inverter branch does not switch seamlessly, and there will be a short period of no input power supply state, and true uninterruptible power supply cannot be achieved.

[0005] The present invention solves the above technical problems through the following technical means: A network-forming UPS includes a static bypass branch and an auxiliary power supply branch with an inverter. The commercial power is input to the static bypass branch to supply power to the load, and the rectified input flows into the load through the auxiliary power supply branch. The static bypass branch and the auxiliary power supply branch form a voltage source parallel connection. A charging circuit and / or a discharging circuit are connected in series on the auxiliary power supply branch, and at least one of the charging circuit and the discharging circuit is an isolated circuit.

[0006] Further, the inverter operates in a droop control strategy or a VSG mode. The no-load voltage control target of the inverter is the commercial power voltage input to the static bypass branch, and the no-load frequency control target of the inverter is the commercial power frequency input to the static bypass branch, so that the static bypass branch and the auxiliary power supply branch form a voltage source parallel connection.

[0007] Further, the isolated circuit is an isolated DCDC.

[0008] Further, the auxiliary power supply branch includes a rectifier, a battery, and an inverter. The rectified input supplies power to the rectifier. The output end of the rectifier is connected to the input end of the battery. The output end of the battery is connected to the input end of the inverter. The output of the inverter supplies power to the load.

[0009] Furthermore, the auxiliary power supply branch further includes a discharging circuit. The output end of the battery is connected to the input end of the inverter through the discharging circuit.

[0010] Furthermore, the auxiliary power supply branch further includes a charging circuit. The output end of the rectifier is connected to the input end of the battery through the charging circuit.

[0011] Furthermore, the auxiliary power supply branch further includes a charging circuit and a discharging circuit. The output end of the rectifier is connected to the input end of the battery through the charging circuit. The output end of the battery is connected to the input end of the inverter through the discharging circuit.

[0012] Furthermore, a rectifier switch is provided on the line between the rectified input and the rectifier and / or a charging switch is provided on the branch where the output end of the rectifier is connected to the input end of the battery and / or a discharging switch is provided on the branch where the output end of the battery is connected to the input end of the inverter and / or an inverter switch is provided on the line between the inverter and the load.

[0013] Further, the static bypass branch includes a bypass static switch. The commercial power supplies power to the load through the bypass static switch.

[0014] Further, an output switch is provided before the load. The commercial power is input to the static bypass branch and supplies power to the load through the output switch. The rectified input flows into the load through the auxiliary power supply branch and the output switch.

[0015] Further, the network-forming UPS further includes a maintenance bypass branch with a maintenance bypass switch, and the mains power is connected to the load through the maintenance bypass switch.

[0016] The present invention also provides a control method for the above-mentioned network-forming UPS, and the method includes:

[0017] When the UPS is operating normally, since the static bypass branch and the auxiliary power supply branch form a parallel connection of voltage sources, the static bypass branch and the auxiliary power supply branch supply power to the load simultaneously. When the mains power fails, the auxiliary power supply branch supplies power to the load alone. A charging circuit and / or a discharging circuit are connected in series on the auxiliary power supply branch, and at least one of the charging circuit and the discharging circuit is an isolated circuit, which increases the loop common-mode impedance when the static bypass branch and the auxiliary power supply branch are connected in parallel at both the input and the output.

[0018] The advantages of the present invention are as follows:

[0019] (1) In the present invention, the static bypass branch and the auxiliary power supply branch form a parallel connection of voltage sources, so that the static bypass branch and the auxiliary power supply branch supply power simultaneously. When there is a mains power failure, the auxiliary power supply branch is still in the power supply state, and there is no short-term state of no input power supply, thus realizing true uninterrupted power supply.

[0020] (2) In the present invention, the inverter operates in a droop strategy or a VSG mode. The control target of the no-load voltage of the inverter is the mains voltage input by the bypass, and the control target of the no-load frequency is the mains frequency input by the bypass. Therefore, the voltage command of the VSG or droop control of the inverter is the grid voltage value, and the frequency is the grid frequency. Thus, the static bypass branch and the auxiliary power supply branch form a parallel connection of voltage sources, so that the two branches can supply power simultaneously. When there is no power in the mains, the loop where the inverter is located will supply power continuously without interruption, thus forming a true uninterruptible power supply.

[0021] (3) In the present invention, when there is mains power, by setting the on / off of each switch, the output of the loop where the inverter is located can be reduced as much as possible when there is mains power, thereby improving the system efficiency.

[0022] (4) In the prior art, the bypass branch and the inverter loop cannot supply power simultaneously, because if they supply power simultaneously, there will be a large circulating current. However, in the present invention, the inverter operates in a droop strategy or a VSG mode to realize the simultaneous power supply of the two branches, and at least one of the charging circuit and the discharging circuit is an isolated circuit. The isolated circuit is an isolated DCDC, which increases the loop common-mode impedance when the static bypass branch and the auxiliary power supply branch are connected in parallel at both the input and the output, so as to reduce the high-frequency common-mode circulating current of the system. Thus, the overall scheme truly realizes uninterrupted power supply and reduces the common-mode circulating current during the uninterrupted power supply process. Description of the Drawings

[0023] Figure 1 Schematic diagram of the prior art UPS

[0024] Figure 2 Schematic diagram of a grid-forming UPS structure disclosed in Embodiment 1 of the present invention

[0025] Figure 3 Schematic diagram of a grid-forming UPS structure disclosed in Embodiment 2 of the present invention

[0026] Figure 4 Schematic diagram of a grid-forming UPS structure disclosed in Embodiment 3 of the present invention Detailed implementation manners

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Embodiment 1

[0029] As Figure 2 shown, Embodiment 1 of the present invention provides a grid-forming UPS, which includes a static bypass branch, an auxiliary power supply branch with an inverter 7, and a maintenance bypass branch with a maintenance bypass switch 1. The commercial power is used as the input of the bypass branch and is connected to the load 2 through the maintenance bypass switch 1. The static bypass branch includes a bypass static switch 3, and the commercial power supplies the load 2 through the bypass static switch 3. The auxiliary power supply branch includes a rectifier 4, a battery 5, a discharge circuit 6, and an inverter 7. The rectifier input supplies power to the rectifier 4. The rectifier input can also use the commercial power input from the bypass branch. The output end of the rectifier 4 is connected to the input end of the battery 5. The output end of the battery 5 is connected to the input end of the inverter 7 through the discharge circuit 6, and the output of the inverter 7 supplies power to the load 2. It should be noted that the grid-forming UPS is an uninterruptible power supply, and only the inverter 7 involved therein can use a grid-forming inverter 7, so the entire UPS is named a grid-forming UPS.

[0030] As a further improved solution, in the implementation of the present invention, the discharge circuit 6 is an isolated DCDC.

[0031] As a further improved solution, in the embodiment of the present invention, the inverter 7 operates in a droop control strategy or a VSG (Virtual Synchronous Generator) mode. The no-load voltage control target of the inverter 7 is the commercial power voltage input by the static bypass branch, and the no-load frequency control target of the inverter 7 is the commercial power frequency input by the static bypass branch, so that the static bypass branch and the auxiliary power supply branch form a voltage source parallel connection.

[0032] The present invention uses an isolated DC-DC as the discharge circuit of the battery to supply power to the inverter 7, and then the inverter 7 directly forms a parallel relationship with the output of the bypass switch branch using the VSG or drooping voltage source characteristic. For traditional UPSs, the output of the priority bypass branch is used for power supply, and the inverter circuit is in standby. When the mains power fails and there is no bypass output, it switches to the inverter circuit for power supply. This switching process is generally at the millisecond level, that is, within this millisecond-level time, the UPS has no output. Moreover, the bypass branch and the inverter circuit cannot supply power simultaneously because if they do, there will be a large circulating current. The output of the static bypass branch of the present invention forms a voltage source parallel connection with the output of the auxiliary power supply branch with the inverter 7. Since the auxiliary power supply branch with the inverter 7 adopts the VSG or drooping mode, the voltage command of the VSG or drooping control of the auxiliary power supply branch with the inverter 7 is the grid voltage value, and the frequency is the grid frequency. As much as possible when there is mains power, the output of the inverter circuit is reduced to improve the system efficiency. When there is no mains power, the auxiliary power supply branch with the inverter 7 will supply power directly without interruption, thus constituting an uninterruptible power supply in the true sense. The purpose of emphasizing the isolated DC-DC is to increase the loop common-mode impedance when both the input and output of the auxiliary power supply branch and the static bypass branch are in parallel, so as to reduce the high-frequency common-mode circulating current of the system.

[0033] In addition, for the convenience of controlling the on / off of each branch in practical applications, a rectifier switch 8 can be provided on the line between the rectifier input and the rectifier 4 in this embodiment, or the rectifier switch 8 can not be provided, without special limitation. The rectifier switch 8 is provided in this embodiment. A charging switch 9 can be provided or not provided on the branch where the output end of the rectifier 4 and the input end of the battery 5 are located, without special limitation. The charging switch 9 is provided in this embodiment. A discharge switch 10 is provided on the branch where the output end of the battery 5 and the input end of the inverter 7 are located, or the discharge switch 10 can not be provided, without special limitation. The discharge switch 10 is provided in this embodiment. An inverter switch 11 is provided on the line between the inverter 7 and the load 2, or the inverter switch 11 can not be provided, without special limitation. The inverter switch 11 is provided in this embodiment. An output switch 12 can also be provided before the load 2. The mains input static bypass branch supplies power to the load 2 through the output switch 12, and the rectifier input flows into the load 2 through the auxiliary power supply branch and the output switch 12. The switch 12 can also not be provided. When there is mains power, by setting the on / off of each switch, as much as possible when there is mains power, the output of the loop where the inverter 7 is located can be reduced to improve the system efficiency. In this embodiment, a bypass maintenance branch and a bypass maintenance switch 1 are provided. Actually, the bypass maintenance branch and the bypass maintenance switch 1 can also not be provided.

[0034] Embodiment 2

[0035] The difference between Embodiment 2 and Embodiment 1 of the present invention lies in that the auxiliary power supply branch further includes a charging circuit 13, and the output end of the rectifier 4 is connected to the input end of the battery 5 through the charging circuit 13. And a discharge circuit 6 is not provided on the auxiliary power supply branch. The charging circuit 13 is an isolated DCDC. For details, refer to Figure 3 .

[0036] Embodiment 3

[0037] The difference between Embodiment 3 and Embodiment 1 of the present invention lies in that not only a discharge circuit 6 but also a charging circuit 13 are provided on the auxiliary power supply branch. The output end of the rectifier 4 is connected to the input end of the battery 5 through the charging circuit 13, and the output end of the battery 5 is connected to the input end of the inverter 7 through the discharge circuit 6. At least one of the charging circuit 13 and the discharge circuit 6 is an isolated DCDC. For details, refer to Figure 4 .

[0038] In the above three embodiments, the common-mode impedance of the auxiliary power supply branch with the inverter 7 is increased through an isolated DCDC. Other solutions such as using an isolated rectifier, an isolated inverter, or connecting a common-mode inductor in series in the auxiliary power supply branch to increase the common-mode impedance of the auxiliary power supply branch to suppress the high-frequency circulating current between the auxiliary power supply branch and the static bypass branch are all within the protection scope of this application.

[0039] Through the above technical solutions, in the prior art, the bypass branch and the inverter circuit cannot supply power simultaneously because if they supply power simultaneously, there will be a large circulating current. However, in the present invention, the inverter 7 operates in a droop strategy or a VSG mode to achieve simultaneous power supply of the two branches, and at least one of the charging circuit 13 and the discharge circuit 6 is an isolated circuit. The isolated circuit is an isolated DCDC, which increases the common-mode impedance of the loop when the static bypass branch and the auxiliary power supply branch are connected in parallel at both the input and output ends, so as to reduce the high-frequency common-mode circulating current of the system. Thus, the overall solution truly realizes uninterrupted power supply and simultaneously reduces the common-mode circulating current during the uninterrupted power supply process.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A network-forming UPS, characterized in that, It includes a static bypass branch and an auxiliary power supply branch with an inverter. The mains input is fed to the load through the static bypass branch, and the rectified input flows into the load through the auxiliary power supply branch. The static bypass branch and the auxiliary power supply branch form a parallel connection of voltage sources. A charging circuit and / or a discharging circuit are connected in series on the auxiliary power supply branch, and at least one of the charging circuit and the discharging circuit is an isolated circuit.

2. The networking type UPS according to claim 1, characterized in that, The inverter operates in a droop control strategy or a VSG mode. The no-load voltage control target of the inverter is the mains voltage input by the static bypass branch, and the no-load frequency control target of the inverter is the mains frequency input by the static bypass branch, so that the static bypass branch and the auxiliary power supply branch form a parallel connection of voltage sources.

3. The network-forming UPS according to claim 1, wherein, The isolated circuit is an isolated DCDC.

4. A networking UPS according to claim 1, characterized in that, The auxiliary power supply branch includes a rectifier, a battery, and an inverter. The rectified input supplies power to the rectifier. The output end of the rectifier is connected to the input end of the battery. The output end of the battery is connected to the input end of the inverter. The output of the inverter is supplied to the load.

5. A networking UPS according to claim 4, characterized in that, The auxiliary power supply branch further includes a discharging circuit. The output end of the battery is connected to the input end of the inverter through the discharging circuit.

6. The network-forming UPS according to claim 4, wherein The auxiliary power supply branch further includes a charging circuit. The output end of the rectifier is connected to the input end of the battery through the charging circuit.

7. A networking UPS according to claim 4, characterized in that, The auxiliary power supply branch further includes a charging circuit and a discharging circuit. The output end of the rectifier is connected to the input end of the battery through the charging circuit. The output end of the battery is connected to the input end of the inverter through the discharging circuit.

8. A networking UPS according to claim 4, characterized in that A rectifying switch is provided on the line between the rectified input and the rectifier and / or a charging switch is provided on the branch where the output end of the rectifier is connected to the input end of the battery and / or a discharging switch is provided on the branch where the output end of the battery is connected to the input end of the inverter and / or an inverting switch is provided on the line between the inverter and the load.

9. The network-forming UPS according to claim 1, wherein The static bypass branch includes a bypass static switch. The mains supplies power to the load through the bypass static switch.

10. A networking UPS according to claim 1, characterized in that, An output switch is provided before the load. The mains input to the static bypass branch supplies power to the load through the output switch. The rectified input flows into the load through the auxiliary power supply branch and the output switch.

11. A networking UPS according to claim 1, characterized in that, It further includes a maintenance bypass branch with a maintenance bypass switch. The mains is connected to the load through the maintenance bypass switch.

12. A control method for a network-forming UPS according to any one of claims 1-11, characterized in that, The method includes: When the UPS is operating normally, since the static bypass branch and the auxiliary power supply branch form a parallel connection of voltage sources, the static bypass branch and the auxiliary power supply branch supply power to the load simultaneously. When the mains power fails, the auxiliary power supply branch supplies power to the load alone. A charging circuit and / or a discharging circuit are connected in series on the auxiliary power supply branch, and at least one of the charging circuit and the discharging circuit is an isolated circuit, which increases the loop common-mode impedance when the input and output of the static bypass branch and the auxiliary power supply branch are both in parallel.

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