High-reliability low-cost cyclic backup uninterruptible power supply

Abstract

The invention relates to the field of power supply management, and discloses a high-reliability low-cost cyclic backup uninterruptible power supply, which comprises N independent power supply uninterruptible power supply devices distributed in different areas for mutual cyclic backup, wherein the output of the (N-1) th uninterruptible power supply is supplied to the load and is also sent to the output of the Nth uninterruptible power supply; the output of the Nth uninterruptible power supply is supplied to the load and is also sent to the output of the first uninterruptible power supply; the power supply of the N uninterruptible power supplies realizes interconnection and uninterruptible power supply conversion through the corresponding output power supply conversion modules and the control of the output power supply conversion modules; n is a preset value. According to the invention, the uninterruptible power supplies in all areas are cyclically interconnected with the minimum cost and the simplest and most reliable mode to form a backup power supply network, so that the power supply reliability is improved.

Description

Technical Field

[0001] The invention relates to the field of power management, and in particular to a high-reliability, low-cost, cyclic backup uninterruptible power supply. Background Art

[0002] Uninterruptible power supplies have been widely used in places where high power supply reliability is required, such as nuclear power, chemical industry, coal mining, electricity, communications, ships, data centers, etc.

[0003] Usually, multiple uninterruptible power supply devices are configured for the loads in a certain area to provide power supply in different areas. For the uninterruptible power supply devices configured for the loads in each area, once the uninterruptible power supply in the area fails, the loads in the area will still have the problem of power outage. To ensure the uninterruptible power supply in the area, on the one hand, it is necessary to improve the fault ride-through capability of the uninterruptible power supply to ensure the uninterruptible power supply of the equipment, and on the other hand, it is necessary to ensure the timely power supply of the loads in the area when the uninterruptible power supply fails. To ensure the timely power supply of the loads in the area, on the one hand, it is necessary to conduct rapid troubleshooting and maintenance; on the other hand, it is necessary to manually connect cables from other power supply ends to supply power; the workload of repairing and restoring power supply is large, the cost is high, and it will cause the loads to lose power for a long time, which will have a great impact on the power supply load and easily cause major losses and consequences.

[0004] In order to improve the reliability and continuity of power supply and take costs into consideration, a more reliable and low-cost emergency power grid structure and control strategy are urgently needed. The uninterruptible power supplies in different areas can be combined to form redundant backups, and continuous and reliable power supply to important loads can be achieved through automatic switching control. At the same time, the improved short-circuit fault ride-through control strategy can maximize the successful and rapid ride-through of short-circuit faults, isolate short-circuit fault points, reduce power outage time, and automatically restore to high-quality inverter power supply to ensure continuous and uninterrupted high-quality power supply output. Summary of the invention

[0005] The purpose of the present invention is to propose a highly reliable and low-cost cyclic backup uninterruptible power supply and a short-circuit ride-through control method thereof, so as to solve the technical problems in the prior art that uninterruptible power supplies in different areas have no redundant backup and cannot automatically switch control and quickly realize short-circuit fault ride-through without significantly increasing costs, thereby improving the output reliability and continuity of the uninterruptible power supply.

[0006] The present invention provides a highly reliable and low-cost cyclic backup uninterruptible power supply, comprising:

[0007] N independent power supply uninterruptible power supplies distributed in different areas, each of which includes a rectifier module, an inverter module, a DC module, a charging module and a power conversion module;

[0008] The rectifier module converts the AC 380V electricity into high-voltage DC electricity, the DC module converts the battery pack electricity into high-voltage DC electricity, the high-voltage DC electricity is connected in parallel to the inverter module input, the inverter module converts the high-voltage DC electricity into AC 220V electricity, the charging module converts the high-voltage DC electricity into battery pack electricity, and the power supply conversion module realizes automatic, fast and uninterrupted power supply conversion of multiple AC 220V electricity;

[0009] The output of the first uninterruptible power supply not only supplies the load, but also supplies the output of the second uninterruptible power supply;

[0010] The output of the second uninterruptible power supply not only supplies the load, but also supplies the output of the third uninterruptible power supply; until,

[0011] The output of the N-1th uninterruptible power supply not only supplies the load, but also supplies the output of the Nth uninterruptible power supply;

[0012] The output of the Nth uninterruptible power supply not only supplies the load, but is also sent to the output of the first uninterruptible power supply;

[0013] The power supply of N uninterruptible power supplies is interconnected and uninterruptible power supply conversion is achieved through corresponding output power supply conversion modules and their control; N is a preset value.

[0014] Furthermore, the output power conversion module of the i-th uninterruptible power supply includes: thyristor SCRi_1, thyristor SCRi_2, thyristor SCRi_3, contactor KMi_1, contactor KMi_2, contactor KMi_3, and contactor KMi for circulating power supply, wherein i is the serial number of the uninterruptible power supply, i=1,2,3…N.

[0015] Furthermore, each uninterruptible power supply includes four power supply modes, namely: bypass 220V power, AC 380V power supply through inverter output 220V power, battery pack power supply through inverter output 220V power and circulating backup 220V power of another uninterruptible power supply connected to it.

[0016] Further, the bypass 220V power of the i-th uninterruptible power supply is respectively connected to one end of the thyristor SCRi_1 and the contactor KMi_1, the other end of the thyristor SCRi_1 is interconnected with one end of the thyristor SCRi_2, the thyristor SCRi_3, and the contactor KMi_2, and the other end of the thyristor SCRi_2 is connected to the inverter output 220V power of the i-th uninterruptible power supply;

[0017] The other end of the thyristor SCRi_3 is connected to one end of the circulating backup power supply contactor KMi-1 of the i-1th uninterruptible power supply to receive the circulating backup 220V power. One end of the contactor KMi_1 is interconnected with the contactor KMi_3 and is connected to the other end of the contactor KMi_2, and is sent to the AC output bus together. The output bus is connected to the output distribution switches QLi_1~QLi_5 and one end of the circulating power supply contactor contactor KMi. The other ends of the distribution switches QLi_1~QLi_5 are respectively sent to the corresponding local power supply loads, and the other end of KMi is sent to the circulating backup bypass input end of another i+1th uninterruptible power supply.

[0018] Furthermore, the bypass power supplies of the N uninterruptible power supplies are from the same power supply, and the inverter power supply and the bypass power supply in each uninterruptible power supply are synchronized through synchronous phase-locked control to ensure phase consistency.

[0019] A control method for a high-reliability, low-cost, cyclic backup uninterruptible power supply is applied to a high-reliability, low-cost, cyclic backup uninterruptible power supply. The method is as follows: the driving control signals of thyristors SCRi_1, thyristors SCRi_2 and thyristors SCRi_3 in the i-th uninterruptible power supply come from a centralized control module, and only one path is turned on at any time.

[0020] Furthermore, the contactors KMi_1, KMi_2 and KMi_3 in the i-th uninterruptible power supply are interlocked together through the manual power supply conversion switch and the control system, and will not be turned on at the same time.

[0021] The KMi contactor for the i-th cycle power supply is closed only when the uninterruptible power supply inverter is normal.

[0022] Compared with the non-cyclic backup device, the i-th cyclic backup device only adds thyristor SCRi_3, contactor KMi_3, and contactor KMi in hardware, with small changes, low cost and improved power supply reliability.

[0023] On the basis of adding cyclic backup power supply control, the uninterruptible power supply further adopts an improved fault ride-through control method. When a short circuit fault occurs in a load branch, the fault branch switch is preferentially tripped through the output current limiting of the inverter module for a certain period of time. If the short circuit fault is not eliminated after this time, it will automatically switch to bypass power supply, and use the large impact current of the bypass to disconnect the branch switch, greatly reducing the power loss time during the fault ride-through process. After the short circuit fault is eliminated and the output current returns to the normal output current range, it will automatically switch to the inverter module for power supply, and the power supply reliability and continuity will be higher.

[0024] The beneficial effects provided by the present invention are: in a simple, reliable and low-cost manner, the uninterruptible power supplies of various regions are cyclically interconnected to form a backup power supply network. On the basis of improving the reliability of equipment and enabling the equipment to have fault ride-through, the power supply reliability of the system is further improved, that is, when the uninterruptible power supply of a certain area fails, the uninterruptible power supplies of other areas in the cyclic interconnection ensure continuous uninterruptible power supply to the power-losing area through an automatic switching control strategy, and at the same time provide sufficient troubleshooting and repair recovery time for the uninterruptible power supplies in the power-losing area; the proposed fault ride-through control method combines the inverter module fault ride-through control and the bypass fault ride-through control, and at the same time has automatic switching and inverter power supply recovery control after fault ride-through, reduces the fault ride-through requirements for the inverter module and improves the success rate of fault ride-through, reduces the power outage time during the fault ride-through process, and further improves the power supply reliability and continuity, which has important practical significance and engineering application value for improving the power supply reliability of the emergency power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the principle of the uninterruptible power supply circuit of the present invention;

[0026] Figure 2 A schematic diagram of the working mode of working condition 1 in this embodiment is shown;

[0027] Figure 3 The working mode schematic diagram of working condition 2 in this embodiment is shown;

[0028] Figure 4 The working mode schematic diagram of working condition 3 in this embodiment is shown;

[0029] Figure 5 The working mode schematic diagram of working condition 4 in this embodiment is shown;

[0030] Figure 6 The working mode schematic diagram of working condition 5 in this embodiment is shown;

[0031] Figure 7 The working mode schematic diagram of working condition 6 in this embodiment is shown;

[0032] Figure 8 The working mode schematic diagram of working condition 7 in this embodiment is shown;

[0033] Fig. 9 It shows a schematic diagram of the inverter module entering the short-circuit current limiting operation when a short circuit occurs at the lower end of QL1_1 in this embodiment;

[0034] Fig.10 It shows a schematic diagram of the inverter module short-circuit fault riding successfully in this embodiment, QL1_1 trips, and the inverter supplies power normally;

[0035] Fig.11The schematic diagram of the operation of the inverter module in this embodiment when the inverter module fails to ride through a short circuit fault and switches to bypass power supply with a large current flowing through QL1_1 is shown;

[0036] Fig.12 It shows a schematic diagram of bypass power supply short circuit fault successfully riding through in this embodiment, QL1_1 trips, and bypass power supply is normal;

[0037] Fig.13 A schematic diagram showing the recovery to normal inverter power supply after bypass power supply short-circuit fault traversal is successful in this embodiment;

[0038] Fig.14 The short-circuit fault ride-through logic control block diagram of this embodiment (short-circuit fault protection logic flow chart as shown in FIG. Fig.14 shown). DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0040] Before formally describing the present invention, the scheme of the present invention is first generally described for easy understanding.

[0041] Please refer to Figure 1 , Figure 1 It is a schematic diagram of the principle of the uninterruptible power supply circuit of the present invention;

[0042] The present invention provides a highly reliable and low-cost cyclic backup uninterruptible power supply, comprising: N independent power supply uninterruptible power supplies distributed in different areas, each uninterruptible power supply comprising a rectifier module, an inverter module, a DC module, a charging module and a power supply conversion module;

[0043] The rectifier module converts the AC 380V electricity into high-voltage DC electricity, the DC module converts the battery pack electricity into high-voltage DC electricity, the high-voltage DC electricity is connected in parallel to the inverter module input, the inverter module converts the high-voltage DC electricity into AC 220V electricity, the charging module converts the high-voltage DC electricity into battery pack electricity, and the power supply conversion module realizes automatic, fast and uninterrupted power supply conversion of multiple AC 220V electricity;

[0044] The output of the first uninterruptible power supply not only supplies the load, but also supplies the output of the second uninterruptible power supply;

[0045] The output of the second uninterruptible power supply not only supplies the load, but also supplies the output of the third uninterruptible power supply; until,

[0046] The output of the N-1th uninterruptible power supply not only supplies the load, but also supplies the output of the Nth uninterruptible power supply;

[0047] The output of the Nth uninterruptible power supply not only supplies the load, but is also sent to the output of the first uninterruptible power supply;

[0048] The power supply of N uninterruptible power supplies is interconnected and uninterruptible power supply conversion is achieved through corresponding output power supply conversion modules and their control; N is a preset value.

[0049] Among them, on the basis of adding cyclic backup power supply control, the above-mentioned uninterruptible power supply further adopts an improved fault ride-through control method. When a short circuit fault occurs in a load branch, the fault branch switch is preferentially tripped by the output current limiting of the inverter module for a certain period of time. If the short circuit fault is not eliminated after the time, it will automatically switch to bypass power supply, and disconnect the branch switch through the large impact current of the bypass, thereby reducing the fault ride-through requirements for the inverter module and improving the success rate of fault ride-through, reducing the power outage time during the fault ride-through process, and after the short circuit fault is eliminated and the output current returns to the normal output current range, it will automatically switch to the inverter module for power supply again, and the power supply reliability and continuity will be higher.

[0050] As an embodiment, the present invention is described by taking N=3 as an example.

[0051] It should be noted that each uninterruptible power supply has four power supply modes, namely: bypass 220V power, AC 380V output 220V power through inverter, battery output 220V power through inverter, and cyclic backup 220V power from another uninterruptible power supply connected to it;

[0052] Among them, the output power supply conversion module of the 1# uninterruptible power supply includes thyristor SCR1_1, thyristor SCR1_2, thyristor SCR1_3, contactor KM1_1, contactor KM1_2, contactor KM1_3, and contactor KM1 for circulating power supply;

[0053] The output power supply conversion module of the 2# uninterruptible power supply includes thyristor SCR2_1, thyristor SCR2_2, thyristor SCR2_3, contactor KM2_1, contactor KM2_2, contactor KM2_3, and contactor KM2 for circulating power supply;

[0054] The output power supply conversion module of the 3# uninterruptible power supply includes thyristor SCRN_1, thyristor SCRN_2, thyristor SCRN_3, contactor KMN_1, contactor KMN_2, contactor KMN_3, and contactor KMN for circulating power supply.

[0055] The connections between the various uninterruptible power supplies are as follows:

[0056] The bypass 220V power of 1# uninterruptible power supply is connected to one end of thyristor SCR1_1 and contactor KM1_1 respectively. The other end of thyristor SCR1_1 is interconnected with one end of thyristor SCR1_2, thyristor SCR1_3 and contactor KM1_2. The other end of thyristor SCR1_2 is connected to the inverter 220V power of 1# uninterruptible power supply. The other end of thyristor SCR1_3 is connected to one end of the circulating backup power supply contactor KMN of N# uninterruptible power supply, receiving the circulating The other end of the backup 220V power, KM1_1, is interconnected with the contactor KM1_3 and connected to the other end of the contactor KM1_2, and sent to the AC output bus. The output bus is connected to the output distribution switch QL1_1~QL1_5 and one end of the circulating power supply contactor KM1. The other ends of the distribution switches QL1_1~QL1_5 are respectively sent to the corresponding local power supply loads, and the other end of the circulating power supply contactor KM1 is sent to the circulating backup bypass input end of the other 2# uninterruptible power supply;

[0057] The bypass 220V power of the 2# uninterruptible power supply is connected to one end of the thyristor SCR2_1 and the contactor KM2_1 respectively. The other end of the thyristor CR2_1 is interconnected with one end of the thyristor SCR2_2, thyristor SCR2_3, and KM2_2. The other end of the thyristor SCR2_2 is connected to the inverter 220V power of the 2# uninterruptible power supply. The other end of the thyristor SCR2_3 is connected to one end of the circulating backup power supply contactor KM1 of the 1# uninterruptible power supply, receiving the circulating backup. 220V electricity, the other end of contactor KM2_1 is interconnected with contactor KM2_3, and connected to the other end of contactor KM2_2, and sent to the AC output bus together. The output bus is connected to the output distribution switch QL2_1~QL2_5 and one end of the circulating power supply contactor KM2. The other ends of the distribution switches QL2_1~QL2_5 are respectively sent to the corresponding local power supply loads, and the other end of the circulating power supply contactor KM2 is sent to the circulating backup input end of another 3# uninterruptible power supply;

[0058] The bypass 220V power of the 3# uninterruptible power supply is connected to one end of the thyristor SCR3_1 and the contactor KM3_1 respectively. The other end of the thyristor SCR3_1 is interconnected with the thyristor SCR3_2, thyristor SCR3_3, and one end of the contactor KM3_2. The other end of the thyristor SCR3_2 is connected to the inverter 220V power of the 3# uninterruptible power supply. The other end of the thyristor SCR3_3 is connected to one end of the cyclic backup power supply contactor KM2 of the 2# uninterruptible power supply, receiving the cyclic backup power supply. The other end of contactor KM3_1 is interconnected with contactor KM2_3 and connected to the other end of contactor KM2_2, and sent to the AC output bus together. The output bus is connected to the output distribution switch QL3_1~QL3_5 and one end of the circulating power supply contactor KM3. The other ends of the distribution switches QL3_1~QL3_5 are sent to the corresponding local power supply loads respectively, and the other end of the circulating power supply contactor KM3 is sent to the circulating backup bypass input end of another 1# uninterruptible power supply.

[0059] The bypass power supplies of 1# to 3# uninterruptible power supplies come from the same power supply, and the inverter power supply and bypass power supply in each uninterruptible power supply are synchronized through synchronous phase-locked control to ensure phase consistency;

[0060] Wherein, i=1-3, the driving control signals of thyristor SCRi_1, thyristor SCRi_2 and thyristor SCRi_3 in each uninterruptible power supply come from the centralized control module, and only one way is turned on at any time to avoid parallel connection of power supplies through thyristors, and realize automatic uninterruptible power supply conversion of 3 power supplies at the same time;

[0061] Wherein, i=1~3, the contactors KMi_1, KMi_2 and KMi_3 in each uninterruptible power supply realize contactor interlocking control through the manual power supply conversion switch and the control system, and will not be turned on at the same time, so as to avoid the power supply being connected in parallel through the contactor;

[0062] Among them, i=1~3, the KMi contactor for circulating power supply is closed only when the inverter power supply of the uninterruptible power supply is normal, that is, once the inverter power supply fails, the uninterruptible power supply will stop circulating power supply to the outside.

[0063] Among them, i = 1 ~ 3, each cyclic backup device only adds thyristor SCRi_3, contactor KMi_3, contactor KMi compared to the non-cyclic backup device hardware, with small changes, low cost and improved power supply reliability;

[0064] Among them, i = 1 ~ 3, each uninterruptible power supply adopts an improved fault ride-through control strategy, and the cyclic backup device only adds thyristor SCRi_3, contactor KMi_3, and contactor KMi to the non-cyclic backup device hardware, with small changes, low cost, and improved power supply reliability;

[0065] Among them, on the basis of adding cyclic backup power supply control, the uninterruptible power supply adopts improved fault ride-through control. When a short circuit fault occurs in a load branch, the faulty branch switch is preferentially tripped through the output current limiting of the inverter module for a certain period of time. If the short circuit fault is not eliminated after the time, it will automatically switch to bypass power supply, and disconnect the branch switch through the large impact current of the bypass. After the short circuit fault is eliminated and the output current returns to the normal output current range, it will automatically switch to the inverter module for power supply again, and the power supply reliability and continuity will be higher.

[0066] The basic working principle of the uninterruptible power supply for cyclic backup power supply and its short-circuit ride-through control of the present invention is:

[0067] (1) Each uninterruptible power supply includes 4 inputs and 3 outputs, which are AC 380V or battery inverter 220V power supply, bypass 220V power supply and cyclic backup 220V power supply from the adjacent uninterruptible power supply;

[0068] (2) The above-mentioned inverter 220V power supply and bypass 220V power supply are synchronously phase-locked to achieve phase consistency;

[0069] (3) The uninterruptible power supply preferably uses the above-mentioned inverter 220V power supply, which is sent to the output AC bus through thyristors and contactors to supply power to the load, and at the same time has the ability to provide backup power to adjacent uninterruptible power supplies;

[0070] (4) Once the inverter power supply fails, the corresponding thyristor will be immediately turned off, and the cyclic backup power supply thyristor will be immediately turned on, and the local load will receive the cyclic backup power supply from the adjacent uninterruptible power supply;

[0071] (5) Once the circulating backup power supply fails, the corresponding thyristor will be immediately turned off, and the bypass thyristor will be immediately turned on to continue to ensure the power supply of the local load through the bypass;

[0072] (6) When the inverter power supply is restored, the uninterruptible power supply will automatically switch back to the inverter power supply from the backup or bypass power supply;

[0073] (7) When the thyristor fails, the corresponding contactor can be manually forced to close through the transfer switch to continue to ensure continuous power supply to the load;

[0074] (8) When the uninterruptible power supply needs to be repaired, the corresponding contactor can be manually forced to close to achieve uninterruptible power supply to the load, and the internal part of the uninterruptible power supply can be repaired at the same time;

[0075] (9) Improved fault ride-through control is adopted, that is, when a short circuit fault occurs in a load branch, the fault branch switch is preferentially tripped by output current limiting of the inverter module for a certain period of time. If the short circuit fault is not eliminated after the time, the power supply is automatically switched to the bypass, and the branch switch is disconnected by the large impact current of the bypass. After the short circuit fault is eliminated and the output current returns to the normal output current range, the power supply is automatically switched to the inverter module again;

[0076] (10) The inverter module fault ride-through control and bypass fault ride-through control are combined, and automatic switching and inverter power supply recovery control after fault ride-through are simultaneously provided, thereby reducing the fault ride-through requirements for the inverter module and increasing the success rate of fault ride-through, further improving power supply reliability and continuity.

[0077] Example:

[0078] Figure 2 The working mode schematic diagram of working condition 1 in this embodiment is shown. Under this working condition, 1#, 2#, and 3# uninterruptible power supplies are all working normally and are in the inverter power supply state. They supply power to their corresponding loads through closed thyristors SCR1_2, SCR2_2, and SCR3_2 respectively; at this time, the circulating backup power supply contactors KM1, KM2, and KM3 are closed, ready to provide emergency power supply to the faulty inverter at any time;

[0079] Figure 3 The working mode schematic diagram of working condition 2 in this embodiment is shown. Under this working condition, the inverter power supply of the 1# uninterruptible power supply fails, the 3# uninterruptible power supply provides emergency backup power supply to the 1# uninterruptible power supply, and the 2# uninterruptible power supply and the 3# uninterruptible power supply are still in normal inverter power supply; at this time, the thyristor SCR1_2 in the 1# uninterruptible power supply is disconnected, SCR1_3 is closed, and KM1 is disconnected; the states in the 2# uninterruptible power supply and the 3# uninterruptible power supply remain unchanged, that is, the thyristors SCR2_2 and SCR3_2 are closed, and the cyclic backup power supply contactors KM2 and KM3 are closed;

[0080] Figure 4 The working mode schematic diagram of working condition 3 in this embodiment is shown. Under this working condition, the inverter power supply of the 2# uninterruptible power supply fails, and the 1# uninterruptible power supply provides emergency backup power supply to the 2# uninterruptible power supply, and the 1# uninterruptible power supply and the 3# uninterruptible power supply are still in normal inverter power supply; at this time, the thyristor SCR2_2 in the 2# uninterruptible power supply is disconnected, SCR2_3 is closed, and KM2 is disconnected; the states in the 1# uninterruptible power supply and the 3# uninterruptible power supply remain unchanged, that is, the thyristors SCR1_2 and SCR3_2 are closed, and the cyclic backup power supply contactors KM1 and KM3 are closed;

[0081] Figure 5The working mode schematic diagram of working condition 4 in this embodiment is shown. Under this working condition, the inverter power supply of the 3# uninterruptible power supply fails, the 2# uninterruptible power supply provides emergency backup power supply to the 3# uninterruptible power supply, and the 1# uninterruptible power supply and the 2# uninterruptible power supply are still in normal inverter power supply; at this time, the thyristor SCR3_2 in the 3# uninterruptible power supply is disconnected, SCR3_3 is closed, and KM3 is disconnected; the states in the 1# uninterruptible power supply and the 2# uninterruptible power supply remain unchanged, that is, the thyristors SCR1_2 and SCR2_2 are closed, and the cyclic backup power supply contactors KM1 and KM2 are closed;

[0082] Figure 6 The working mode diagram of working condition 5 in this embodiment is shown. Under this working condition, the inverter power supply of 1# and 2# uninterruptible power supplies fails, 3# uninterruptible power supply provides backup power supply to 1# uninterruptible power supply, and 2# uninterruptible power supply provides bypass power supply; at this time, thyristors SCR1_1 and SCR1_2 in 1# uninterruptible power supply are disconnected, SCR1_3 is closed, and KM1 is disconnected; thyristor SCR2_1 in 2# uninterruptible power supply is closed, SCR2_2 and SCR2_3 are disconnected, and the circulating backup power supply contactor KM2 is disconnected; the state of 3# uninterruptible power supply changes, thyristor SCR3_2 is closed, SCR3_1 and SCR3_3 are disconnected, and the circulating backup power supply contactor KM3 is closed; at this time, if an uninterruptible power supply is restored, its corresponding Figure 2 to Figure 5 Working mode under the conditions shown;

[0083] Figure 7 The working mode diagram of working condition 6 in this embodiment is shown. Under this working condition, the inverter power supply of 1#, 2#, and 3# uninterruptible power supplies fails, and 1#, 2#, and 3# uninterruptible power supplies automatically switch to bypass power supply; at this time, thyristors SCR1_1~SCR3_1 are closed, thyristors SCR1_2~SCR3_2, SCR1_3~SCR3_3 are disconnected, and the circulating backup power supply contactors KM1~KM3 are disconnected; at this time, if an uninterruptible power supply is restored, its corresponding Figure 2 to Figure 5 Working mode under the conditions shown;

[0084] Figure 8 The working mode schematic diagram of working condition 7 in this embodiment is shown. Under this working condition, the 1# uninterruptible power supply is completely failed, including the inverter power supply, bypass power supply and thyristor therein. The circulating backup power supply contactor KM1_3 is forced to be closed through the manual conversion switch, and the 3# uninterruptible power supply provides circulating backup power to it; at this time, the thyristors SCR1_1~SCR1_3 in the 1# uninterruptible power supply are disconnected, KM1_1, KM1_2, and KM1 are disconnected, and KM1_3 is closed; the states in the 2# uninterruptible power supply and the 3# uninterruptible power supply remain unchanged, that is, the thyristors SCR2_2 and SCR3_2 are closed, and the circulating backup power supply contactors KM2 and KM3 are closed; other forced circulating power supply modes are similar.

[0085] Figure 9-13 The schematic diagram of the short-circuit fault ride-through mode in this embodiment is shown. Taking the 1# UPS power supply circuit diagram as an example, before the short-circuit fault occurs, the UPS is in a power supply state of 380V outputting 220V through an inverter. Fig. 9 This is the working mode when a short circuit fault occurs at the lower end of the load branch QL1. At this time, the inverter module enters short-circuit current limiting (constant current output, voltage close to zero), and the constant current flows entirely through the load branch switch QL1_1. After the short-circuit current limiting lasts for a certain period of time, QL1_1 trips, and the inverter module itself successfully rides through the short circuit fault. The inverter module continues to supply power to loads such as QL1_2 to QL1_5. Fig.10 As shown; after the short-circuit current limiting continues for a certain period of time, QL1_1 does not act, and the short-circuit fault is not eliminated. It is preliminarily determined that the inverter short-circuit fault ride-through has failed, the thyristor SCR1_2 is disconnected, SCR1_1 is closed, and it automatically switches to the bypass 220V power supply. At the same time, the inverter module exits the short-circuit current limiting mode and returns to the constant voltage mode. Fig.11 shown in Fig.11 Based on the mode shown, the 220V bypass will generate a larger impact current than the inverter module, flowing through QL1_1 to cause it to trip, eliminating the short circuit fault, and the bypass 220V continues to supply power to loads such as QL1_2~QL1_5. Fig.12 shown in Fig.12 Based on the mode shown, it is judged that the output current is within the normal working range. After the short circuit fault is eliminated, the thyristor SCR1_2 is closed, SCR1_1 is disconnected, and the inverter module is switched back to power supply. Fig.13 It should be noted that if Figure 9-13 If the bypass power supply fails, the inverter module will enter short-circuit current limiting for a longer period of time to maximize the short-circuit fault ride-through.

[0086] Fig.14 The short-circuit fault ride-through control logic diagram of this embodiment is shown. When a short circuit occurs on the load side, the inverter module detects its internal current. After the current exceeds the peak value of 71A and lasts for 10ms, the following judgment is made:

[0087] 1) When the bypass is normal, the thyristor switches to the bypass power supply, the bypass withstands large current, and the fault switch is quickly tripped to reduce the power failure time. When the output current is restored to the rated range after the fault is isolated, it is switched back to the inverter power supply. Under this condition, the fault ride-through time is about 10ms-20ms, and the power failure time is reduced to a minimum.

[0088] 2) When the bypass is abnormal, the inverter power supply continues to time, with a maximum bearing capacity of 120A peak (current limiting operation) for 100ms. If the switch at the fault point trips, the output current returns to normal, and the equipment exits the current limiting and returns to normal power supply, without affecting the operation of other power supply branches. Under this condition, the fault ride-through completion time is about 100ms, which is longer than the above-mentioned fault ride-through time combined with bypass, and the power failure time is longer; if the load current has not returned to normal after running for more than 100ms, it is a short-circuit fault ride-through failure, and the equipment stops output;

[0089] The parameters of the embodiment of the present invention are as follows: Inverter supply voltage V P1 =220VAC, output power capacity P P1 =6kW; bypass supply voltage V P2 =220VAC, output power capacity P P2 =3kW; the total local load power of each uninterruptible power supply is 3kW; SCR1_1~SCR3_1, SCR1_2~SCR3_2, SCR1_3~SCR3_3 are thyristors; KM1_1~KM3_1, KM1_2~KM3_2, KM1_3~KM3_3, KM1~KM3 are AC contactors.

[0090] The beneficial effects provided by the present invention are: in a simple, reliable and low-cost manner, the uninterruptible power supplies of various regions are cyclically interconnected to form a backup power supply network. On the basis of improving the reliability of equipment and enabling the equipment to have fault ride-through, the power supply reliability of the system is further improved, that is, when the uninterruptible power supply of a certain area fails, the uninterruptible power supplies of other areas in the cyclic interconnection ensure continuous uninterruptible power supply to the power-losing area through an automatic switching control strategy, and at the same time provide sufficient troubleshooting and repair recovery time for the uninterruptible power supplies in the power-losing area; the proposed fault ride-through control method combines the inverter module fault ride-through control and the bypass fault ride-through control, and at the same time has automatic switching and inverter power supply recovery control after fault ride-through, reduces the fault ride-through requirements for the inverter module and improves the success rate of fault ride-through, reduces the power outage time during the fault ride-through process, and further improves the power supply reliability and continuity, which has important practical significance and engineering application value for improving the power supply reliability of the emergency power grid.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-reliability, low-cost, cyclic backup uninterruptible power supply, characterized by: include: N independent power supply uninterruptible power supplies distributed in different areas; Each uninterruptible power supply includes a rectifier module, an inverter module, a DC module, a charging module and a power conversion module; The rectifier module converts the AC 380V electricity into high-voltage DC electricity, the DC module converts the battery pack electricity into high-voltage DC electricity, the high-voltage DC electricity is connected in parallel to the inverter module input, the inverter module converts the high-voltage DC electricity into AC 220V electricity, the charging module converts the high-voltage DC electricity into battery pack electricity, and the power supply conversion module realizes automatic, fast and uninterrupted power supply conversion of multiple AC 220V electricity; The output of the first uninterruptible power supply not only supplies the load, but also supplies the output of the second uninterruptible power supply; The output of the second uninterruptible power supply not only supplies the load, but also supplies the output of the third uninterruptible power supply; until, The output of the N-1th uninterruptible power supply not only supplies the load, but also supplies the output of the Nth uninterruptible power supply; The output of the N-1th uninterruptible power supply not only supplies the load, but is also sent to the output of the first uninterruptible power supply; The power supply of N uninterruptible power supplies is interconnected and uninterruptible power supply conversion is achieved through corresponding power supply conversion modules and their control; N is a preset value.

2. A high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 1, characterized in that: The power supply conversion module of the i-th uninterruptible power supply includes: thyristor SCRi_1, thyristor SCRi_2, thyristor SCRi_3, contactor KMi_1, contactor KMi_2, contactor KMi_3, and contactor KMi for circulating power supply, wherein i is the serial number of the uninterruptible power supply, i=1,2,3…N.

3. A high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 2, characterized in that: Each uninterruptible power supply has four power supply modes: bypass 220V power, AC 380V or battery powered inverter output 220V power and circulating backup 220V power from another uninterruptible power supply connected to it.

4. A high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 3, characterized in that: The bypass 220V power of the i-th uninterruptible power supply is connected to one end of the thyristor SCRi_1 and the contactor KMi_1 respectively, the other end of the thyristor SCRi_1 is interconnected with one end of the thyristor SCRi_2, the thyristor SCRi_3, and the contactor KMi_2, and the other end of the thyristor SCRi_2 is connected to the AC380V of the i-th uninterruptible power supply or the battery group power supply inverter output 220V power; The other end of the thyristor SCRi_3 is connected to one end of the circulating backup power supply contactor KMi-1 of the i-1th uninterruptible power supply to receive the circulating backup 220V power. The other end of the contactor KMi_1 is interconnected with the contactor KMi_3 and is connected to the other end of the contactor KMi_2, and is sent to the AC output bus together. The output bus is connected to the output distribution switches QLi_1~QLi_5 and one end of the circulating power supply contactor contactor KMi. The other ends of the distribution switches QLi_1~QLi_5 are respectively sent to the corresponding local power supply loads, and the other end of KMi is sent to the circulating backup input end of another i+1th uninterruptible power supply.

5. A high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 4, characterized in that: The bypass power supplies of N uninterruptible power supplies come from the same power supply, and the inverter power supply and bypass power supply in each uninterruptible power supply are synchronized through synchronous phase-locked control to ensure phase consistency.

6. A control method for a high-reliability, low-cost, cyclic backup uninterruptible power supply, applied to the high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 5, characterized in that: The driving control signals of the thyristor SCRi_1, thyristor SCRi_2 and thyristor SCRi_3 in the i-th uninterruptible power supply come from the centralized control module, and only one path is turned on at any time.

7. A control method for a high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 6, characterized in that: Contactor KMi_1, contactor KMi_2 and contactor KMi_3 in the i-th uninterruptible power supply realize contactor interlocking control through the manual power supply conversion switch and the control system, and will not be turned on at the same time.

8. A control method for a high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 7, characterized in that: The KMi contactor for the i-th cycle power supply is closed only when the uninterruptible power supply inverter is normal.

9. A control method for a high-reliability, low-cost, cyclic backup uninterruptible power supply as claimed in claim 1, characterized in that: The uninterruptible power supply has an improved fault ride-through control. When a short circuit occurs in a branch, the fault branch switch is preferentially tripped through the output current limiting of the inverter module for a certain period of time. If the short circuit fault is not eliminated after the time, it automatically switches to the bypass power supply, and the branch switch is disconnected by the large impact current of the bypass, which reduces the fault ride-through requirements for the inverter module and improves the success rate of fault ride-through, and reduces the power outage time during the fault ride-through process. After the short circuit fault is eliminated and the output current returns to the normal output current range, it automatically switches to the inverter module for power supply.

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