UPS parallel operation bypass current sharing method

Abstract

The invention discloses a UPS parallel operation bypass current sharing method. The UPS parallel operation bypass current sharing method comprises the following steps: selecting a UPS with a minimum cabinet output current effective value in a parallel operation system as a current sharing host, and keeping an SCR (Selective Catalytic Reduction) connected with the current sharing host in parallel on for a long time; and the other UPSs are current-sharing slaves, the current-sharing slaves realize chopping by adjusting the conduction angle of the bypass SCR, and the output current of each UPS is adjusted so as to enable the output current to be within a set current range. According to the invention, bypass current sharing of the parallel operation system can be realized, and the problem of temperature rise is avoided, so that the loading capacity of the whole UPS parallel operation system is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of electric power technology, and in particular to a UPS parallel bypass current equalization method. Background Art

[0002] Uninterruptible Power System (UPS) is a device that can take over the power supply from the mains when there is a power outage. It continues to supply power when the mains is abnormal or when there is a power outage, ensuring that users use electricity safely and reliably. UPS is usually used in parallel with a static transfer switch (STS). When the UPS main circuit fails, the bypass input voltage passes through the STS to supply power to the electrical equipment. STS usually uses a thyristor (Silicon Controlled Rectifier, SCR) as a switch, and its current level matches the UPS power level.

[0003] Figure 1 This is a structural diagram of an existing multiple UPS parallel bypass load circuit. Figure 2 This is an existing current waveform diagram of a multiple UPS parallel bypass load circuit. Figure 1 and Figure 2 When multiple UPS are connected in parallel and bypassed (i.e., distributed bypass), due to differences in line impedance, the bypass currents of each UPS will be unbalanced. If this continues for a long time, it may cause temperature rise problems, reducing the load capacity of the entire UPS parallel system. Summary of the invention

[0004] The present invention provides a UPS parallel bypass current equalization method to achieve bypass current equalization of a parallel system, avoid the problem of temperature rise, and thus improve the load capacity of the entire UPS parallel system.

[0005] According to one aspect of the present invention, a UPS parallel bypass current balancing method is provided, and the UPS parallel bypass current balancing method comprises:

[0006] In the parallel system, a UPS with the smallest effective value of cabinet output current is selected as the current balancing host, and the SCR connected in parallel with the current balancing host is kept on for a long time;

[0007] The remaining UPS are current-sharing slaves, which implement chopping by adjusting the conduction angle of the bypass SCR, and adjust the output current of each UPS so that the output current is within a set current range.

[0008] Optionally, selecting a UPS with the smallest effective value of cabinet output current in the parallel system as the current sharing host includes:

[0009] Send the cabinet information to the bus, receive other cabinet information at the same time, and count the information of all cabinets in the parallel system;

[0010] Determine whether the parallel system has a current-sharing host and obtain a first determination result;

[0011] If the first judgment result is that the parallel system has no current-sharing host, then judging whether the output current of the local cabinet is the smallest, and obtaining a second judgment result;

[0012] If the second judgment result is that the output current of the local cabinet is the smallest, the local cabinet competes to become the current-sharing host;

[0013] If the second judgment result is that the output current of the cabinet is not the minimum, the process returns to continue the competition among the current-sharing hosts.

[0014] Optionally, if the first judgment result is that the parallel system has a current-sharing host, it is determined whether the current-sharing host is the local cabinet to obtain a third judgment result;

[0015] If the third judgment result is that the current balancing host is the cabinet, determine whether the current balancing host needs to be released to obtain a fourth judgment result;

[0016] If the fourth judgment result is that the current sharing host needs to be released, then the current sharing host is released;

[0017] If the fourth judgment result is that the current sharing host does not need to be released, returning to continue the competition for the current sharing host;

[0018] If the third judgment result is that the current sharing host is not the cabinet, the process returns to continue the competition for the current sharing host.

[0019] Optionally, if the fourth judgment result is that the flow balancing host needs to be released, releasing the flow balancing host includes:

[0020] If the current balancing host is not in bypass power supply, releasing the current balancing host;

[0021] Alternatively, if a new cabinet is added to the parallel system, the current sharing host is released;

[0022] Alternatively, if it is counted that there are multiple current-sharing hosts in the parallel system, the current-sharing host is released.

[0023] Optionally, the current sharing slave realizes chopping by adjusting the conduction angle of the bypass SCR, including:

[0024] Determine whether the current sharing slave needs to perform current sharing adjustment and obtain a fifth determination result;

[0025] If the fifth judgment result is that the current sharing slave does not need to perform current sharing regulation, the SCR chopper of the current sharing slave is turned off.

[0026] Optionally, if the fifth judgment result is that the current balancing slave needs to be current balancing adjusted, then when the effective value of the output current of the current balancing slave is greater than the average current output by the parallel system plus a set multiple of the rated output current of a single cabinet of the parallel system, the SCR chopper of the current balancing slave is forward regulated.

[0027] Optionally, if the fifth judgment result is that the current balancing slave needs to be current balancing adjusted, then when the effective value of the output current of the current balancing slave is less than the average current output by the parallel system minus a set multiple of the rated output current of a single cabinet of the parallel system, the SCR chopping of the current balancing slave is reversely adjusted; otherwise, the SCR chopping of the current balancing slave is maintained.

[0028] Optionally, the determining whether the current sharing slave needs to perform current sharing adjustment and obtaining a fifth determination result includes:

[0029] The output current of the parallel system is greater than a set multiple of the rated current, and the cabinet is not a current-sharing host, and the cabinet has no competing current-sharing host.

[0030] Optionally, the SCR chopping forward regulation of the current sharing slave includes:

[0031] If the current output of the current-sharing slave cabinet is greater than the effective value of the average current output by the parallel system, the conduction delay angle needs to be increased.

[0032] Optionally, the SCR chopping reverse regulation of the current sharing slave includes:

[0033] If the current output from the cabinet is less than the effective value of the average current output by the parallel system, the conduction delay angle needs to be reduced.

[0034] The technical solution of the embodiment of the present invention proposes a bypass current sharing control method based on the existing cabinet-type UPS architecture. In the parallel system, a UPS with the smallest cabinet output current effective value is selected as the current sharing host, and the SCR connected in parallel with the current sharing host is kept on for a long time; the remaining UPS are current sharing slaves, and the current sharing slaves realize chopping by adjusting the bypass SCR conduction angle, and adjust the output current of each UPS so that the output current is within the set current range; so as to realize bypass current sharing of the parallel system, avoid temperature rise problems, and thus improve the load capacity of the entire UPS parallel system. In summary, the present invention solves the problem that when multiple UPS are connected in parallel and bypass load, the bypass current of each UPS will be unbalanced, which may cause temperature rise problems in the long run, resulting in a decrease in the load capacity of the entire UPS parallel system.

[0035] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is a structural diagram of an existing multiple UPS parallel bypass load circuit;

[0038] Figure 2 It is an existing current waveform diagram of a bypass load circuit of multiple UPS in parallel;

[0039] Figure 3 is a flow chart of a UPS parallel bypass current sharing method provided according to an embodiment of the present invention;

[0040] Figure 4 A current waveform diagram of a plurality of UPS parallel bypass load circuits after current sharing according to an embodiment of the present invention;

[0041] Figure 5 is a flow chart of another UPS parallel bypass current sharing method provided according to an embodiment of the present invention;

[0042] Figure 6 is a flow chart of another UPS parallel bypass current sharing method provided according to an embodiment of the present invention;

[0043] Figure 7 is a current waveform diagram of an SCR chopper forward regulation provided according to an embodiment of the present invention;

[0044] Figure 8 The figure is a current waveform diagram of SCR chopping reverse regulation provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0047] Figure 3 is a flow chart of a UPS parallel bypass current sharing method provided according to an embodiment of the present invention, referring to Figure 3 The embodiment of the present invention provides a UPS parallel bypass current balancing method, and the UPS parallel bypass current balancing method includes:

[0048] S110. In the parallel system, select a UPS with the smallest effective value of cabinet output current as the current balancing host, and keep the SCR connected in parallel with the current balancing host turned on.

[0049] Specifically, the parallel system can be composed of multiple parallel cabinet UPS. A UPS with the smallest output current effective value is selected from multiple cabinets as the current balancing host, and the SCR connected in parallel with it is kept on for a long time. The competition principle of the current balancing host: During the current balancing regulation process, if all machines participate in the regulation of the SCR conduction angle, it may happen that all UPS bypass SCRs are disconnected at the same time. This will cause the output voltage to be intermittent and cause the risk of load shedding. To avoid this situation, it is necessary to compete for a current balancing host in the parallel system. The current balancing host keeps the SCR on for a long time, and the current balancing slave participates in the current balancing regulation.

[0050] S120 and the other UPS are current-sharing slaves, which realize chopping by adjusting the conduction angle of the bypass SCR, and adjust the output current of each UPS so that the output current is within the set current range.

[0051] Specifically, Figure 4 is a current waveform diagram of a plurality of UPS parallel bypass load circuits after current sharing according to an embodiment of the present invention, with reference to Figure 4 The remaining UPS are current-sharing slaves, and chopping is achieved by adjusting the bypass SCR conduction angle, so that the output current of each UPS is adjusted in the direction of the average current output by the parallel system, and finally reaches a steady state, that is, the bypass current sharing of the parallel system is achieved.

[0052] The technical solution of the embodiment of the present invention proposes a bypass current sharing control method based on the existing cabinet-type UPS architecture. In the parallel system, a UPS with the smallest cabinet output current effective value is selected as the current sharing host, and the SCR connected in parallel with the current sharing host is kept on for a long time; the remaining UPS are current sharing slaves, and the current sharing slaves realize chopping by adjusting the bypass SCR conduction angle, and adjust the output current of each UPS so that the output current is within the set current range; so as to realize bypass current sharing of the parallel system, avoid temperature rise problems, and thus improve the load capacity of the entire UPS parallel system. In summary, the present invention solves the problem that when multiple UPS are connected in parallel and bypass load, the bypass current of each UPS will be unbalanced, which may cause temperature rise problems in the long run, resulting in a decrease in the load capacity of the entire UPS parallel system.

[0053] Figure 5 is a flow chart of another UPS parallel bypass current sharing method provided according to an embodiment of the present invention, referring to Figure 5 Optionally, in the parallel system, selecting a UPS with the smallest effective value of cabinet output current as the current sharing host includes:

[0054] Send the cabinet information to the bus, receive other cabinet information at the same time, and count the information of all cabinets in the parallel system;

[0055] Determine whether the parallel system has a current-sharing host and obtain a first determination result;

[0056] If the first judgment result is that the parallel system has no current-sharing host, then determine whether the output current of this cabinet is the smallest to obtain a second judgment result;

[0057] If the second judgment result is that the output current of this cabinet is the smallest, then this cabinet competes to become the current-sharing host;

[0058] If the second judgment result is that the output current of the cabinet is not the minimum, the process returns to continue the competition for the current-sharing host.

[0059] Specifically, the general principle of the current-sharing host competition is to select the UPS with the smallest effective value of cabinet output current in the parallel system as the current-sharing host before adjusting the current-sharing. Once the current-sharing host is established, it is not fixed and will still need to compete for the current-sharing host again in some special cases.

[0060] First, send the information of this cabinet to the bus and receive the information of other cabinets at the same time; all cabinets will share the information on the data bus, which means that any cabinet can count the information of other cabinets in the system. Then, count the information of all cabinets in the parallel system. Determine whether there is a current-sharing host in the parallel system. If there is no current-sharing host, determine whether the output current of this cabinet is the smallest. If the output current of this cabinet is the smallest, this cabinet competes for the current-sharing host; if the output current of this cabinet is not the smallest, end the process and return to continue the competition for the current-sharing host.

[0061] Continue to refer Figure 5 Optionally, if the first judgment result is that the parallel system has a current-sharing host, then it is determined whether the current-sharing host is the cabinet to obtain a third judgment result;

[0062] If the third judgment result is that the current sharing host is the cabinet, it is determined whether the current sharing host needs to be released to obtain a fourth judgment result;

[0063] If the fourth judgment result is that the current sharing host needs to be released, then the current sharing host is released;

[0064] If the fourth judgment result is that there is no need to release the current sharing host, then return to continue the competition for the current sharing host;

[0065] If the third judgment result is that the current-sharing host is not the cabinet, the process returns to continue the competition for the current-sharing host.

[0066] Specifically, if the parallel system has a current balancing host, determine whether the current balancing host is the local cabinet; if the current balancing host is the local cabinet, determine whether the current balancing host needs to be released; if the current balancing host needs to be released, release it; if the current balancing host does not need to be released, end the process and return to continue the competition for the current balancing host.

[0067] Continue to refer Figure 5 Optionally, if the fourth judgment result is that the current sharing host needs to be released, releasing the current sharing host includes:

[0068] If the current-sharing host is not in bypass power supply, release the current-sharing host;

[0069] Or, if a new cabinet is added to the parallel system, release the current sharing host;

[0070] Alternatively, if it is counted that there are multiple current-sharing hosts in the parallel system, the current-sharing host is released.

[0071] Specifically, to determine whether to release the current-sharing host, certain conditions must be met. The following three situations require the release of the current-sharing host for re-competition: when the current-sharing host is not in bypass power supply, the current-sharing host is released; or, when a new cabinet is added to the parallel system, the current-sharing host is released; or, when multiple current-sharing hosts are counted, the current-sharing host is released.

[0072] It should be noted that the above UPS is a three-phase UPS, each phase of which is controlled independently and will not affect each other. In other words, in theory, each phase will compete for a host.

[0073] Figure 6 is a flow chart of another UPS parallel bypass current sharing method provided according to an embodiment of the present invention, referring to Figure 6 Optionally, the current sharing slave realizes chopping by adjusting the conduction angle of the bypass SCR, including:

[0074] Determine whether the current sharing slave needs to perform current sharing adjustment and obtain a fifth determination result;

[0075] If the fifth judgment result is that the current sharing slave does not need to perform current sharing regulation, the SCR chopper of the current sharing slave is turned off.

[0076] Specifically, the cabinet information is sent to the bus, and the information of other cabinets is received at the same time; all cabinets will share the information on the data bus, which means that any cabinet can count the information of other cabinets in the system. Then, the information of all cabinets in the parallel system is counted. It is determined whether the current sharing slave needs to be regulated. If the current sharing slave does not need to be regulated, the SCR chopper of the current sharing slave is turned off.

[0077] refer to Figure 6 Optionally, if the fifth judgment result is that the current-sharing slave needs to be current-sharing regulated, then when the effective value of the output current of the current-sharing slave is greater than the average current output by the parallel system plus a set multiple of the rated output current of a single cabinet in the parallel system, the SCR chopper of the current-sharing slave is forward regulated.

[0078] refer to Figure 6 Optionally, if the fifth judgment result is that the current balancing slave needs to be current balancing adjusted, then when the effective value of the output current of the current balancing slave is less than the average current output by the parallel system minus the set multiple of the rated output current of a single cabinet in the parallel system, the SCR chopping of the current balancing slave is reversely adjusted; otherwise, the SCR chopping of the current balancing slave is maintained.

[0079] Specifically, the setting multiple can be ±0.5% of the rated output current of a single cabinet in the parallel system. The SCR conduction angle adjustment of the current-sharing slave is bidirectional. When the effective value of the output current of the current-sharing slave is greater than the average current output of the parallel system + 0.5% of the rated output current of a single cabinet in the parallel system, the SCR chopper of the current-sharing slave is adjusted forward; when the effective value of the output current of the current-sharing slave is less than the average current output of the parallel system - 0.5% of the rated output current of a single cabinet in the parallel system, the SCR chopper of the current-sharing slave is adjusted reversely; if not, the current conduction angle is maintained. Among them, the above 0.5% is the hysteresis value to avoid the SCR from adjusting back and forth at the critical load.

[0080] For example, two parallel three-phase UPSs with a rated power of 600K and a rated output voltage of 220V. Phase A carries 200K, and the average current of the parallel system is 200K / 220V / 2=454.5A. Assuming that the phase A of unit 2 is a slave, the rated output current of a single cabinet is 600000W / 3 (phase) / 220V=909A. When the phase A current of unit 2 is greater than 454.5A+909A*0.005=459A, adjust its conduction angle in the forward direction until the phase A current of unit 2 is between (450A, 459A) and the conduction angle is maintained. The purpose of reverse regulation is to adapt to the working conditions of load changes. When the conduction angle calculated previously is too large after the load changes and is no longer applicable to the current load conditions, the conduction angle can be adjusted back. The adjustment principle is the same as that of forward regulation.

[0081] Optionally, determining whether the current sharing slave needs to perform current sharing adjustment and obtaining a fifth determination result includes:

[0082] The output current of the parallel system is greater than the set multiple of the rated current, and this cabinet is not a current-sharing host, and this cabinet has no competing current-sharing host.

[0083] Specifically, the setting multiple can be 30% of the rated current. To determine whether the current sharing slave needs to be adjusted, certain conditions must be met. When the output current of the parallel system is greater than 30% of the rated current, and this cabinet is not the current sharing master, and this cabinet has no competing current sharing master, current sharing adjustment is required.

[0084] In order to ensure the accuracy of current sharing regulation, it is designed that current sharing regulation is not performed under light load, and the light load judgment threshold is 30%, that is, current sharing regulation will only be enabled when the average current of a single cabinet in the parallel system is greater than 30% of the rated current.

[0085] For example, a three-phase UPS with a rated power of 600K and a rated output voltage of 220V is connected in parallel. At this time, the parallel system power is 1200K, and the single-phase rated power is 400K. Then only when one of the three phases A, B, and C meets the load requirement of more than 120KW, that is, the average single-phase output current effective value of a single cabinet is greater than 273A (for example, if the single-phase load of the 2-phase parallel system is 120KW, the average single-phase current of the single cabinet is: 120000W / 220V / 2=273A), the current equalization regulation function will be enabled for that phase.

[0086] Figure 7 is a current waveform diagram of a SCR chopper forward regulation according to an embodiment of the present invention, referring to Figure 7 Optionally, the SCR chopping forward regulation of the current sharing slave includes:

[0087] If the current output from the current-sharing slave cabinet is greater than the average effective value of the parallel system output current, the conduction delay angle needs to be increased.

[0088] Specifically, the delay conduction of the SCR chopper adjustment of the current-sharing slave can move in both directions. If the current output current of the current-sharing slave cabinet is greater than the average current effective value of the parallel system output, it is necessary to increase the conduction delay angle, that is, adjust the conduction angle in the positive direction, such as Figure 7 shown.

[0089] Figure 8 is a current waveform diagram of SCR chopper reverse regulation provided according to an embodiment of the present invention, with reference to Figure 8 , the SCR chopper reverse regulation of the current sharing slave includes:

[0090] If the current output from the cabinet is less than the average effective value of the current output by the parallel system, the conduction delay angle needs to be reduced.

[0091] Specifically, if the current output current from the current-sharing cabinet is less than the average current effective value of the parallel system output, it is necessary to reduce the conduction delay angle, that is, the conduction angle is reversely adjusted until the output current of the cabinet is aligned with the average current effective value of the parallel system output, and the current conduction angle is maintained, such as Figure 8 shown.

[0092] like Figure 7 and Figure 8 As shown, "Time" is the delayed conduction time (the conduction delay angle that needs to be adjusted), and "Cnt" is the delayed conduction counter. When the instantaneous value of the cabinet output current is less than 10% of the rated current, Cnt starts counting until the delayed conduction time is reached, and the control sends out the SCR drive to turn on the SCR.

[0093] It should be noted that: when the effective value of the output current of the current-sharing slave is greater than the average current output of the parallel system + 0.5% of the rated output current of a single cabinet in the parallel system, the SCR chopper of the current-sharing slave is adjusted in a positive direction; when the effective value of the output current of the current-sharing slave is less than the average current output of the parallel system - 0.5% of the rated output current of a single cabinet in the parallel system, the SCR chopper of the current-sharing slave is adjusted in a negative direction. In order to determine whether the conduction angle should be increased or decreased, the effective value of the output current of the current-sharing slave is used. Figure 7 and Figure 8 The specific implementation method of adjusting the conduction angle is shown in the figure, and the instantaneous value of the current is used to determine the starting point of the count.

[0094] Optionally, the adjustment range of the conduction delay angle is 0ms-9ms.

[0095] Specifically, the conduction delay angle adjustment range is 0-9ms (approximately 0-150°).

[0096] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A UPS parallel bypass current equalization method, characterized in that: include: In the parallel system, a UPS with the smallest effective value of cabinet output current is selected as the current balancing host, and the SCR connected in parallel with the current balancing host is kept on for a long time; The remaining UPS are current-sharing slaves, which implement chopping by adjusting the conduction angle of the bypass SCR, and adjust the output current of each UPS so that the output current is within a set current range.

2. The method according to claim 1, characterized in that The method of selecting a UPS with the smallest effective value of cabinet output current as the current sharing host in the parallel system includes: Send the cabinet information to the bus, receive other cabinet information at the same time, and count the information of all cabinets in the parallel system; Determine whether the parallel system has a current-sharing host and obtain a first determination result; If the first judgment result is that the parallel system has no current-sharing host, then judging whether the output current of the local cabinet is the smallest, and obtaining a second judgment result; If the second judgment result is that the output current of the local cabinet is the smallest, the local cabinet competes to become the current-sharing host; If the second judgment result is that the output current of the cabinet is not the minimum, the process returns to continue the competition among the current-sharing hosts.

3. The method according to claim 2, characterized in that If the first judgment result is that the parallel system has a current-sharing host, then judging whether the current-sharing host is the local cabinet, and obtaining a third judgment result; If the third judgment result is that the current balancing host is the cabinet, determine whether the current balancing host needs to be released to obtain a fourth judgment result; If the fourth judgment result is that the current sharing host needs to be released, then the current sharing host is released; If the fourth judgment result is that the current sharing host does not need to be released, returning to continue the competition for the current sharing host; If the third judgment result is that the current sharing host is not the cabinet, the process returns to continue the competition for the current sharing host.

4. The method according to claim 3, characterized in that If the fourth judgment result is that the current sharing host needs to be released, releasing the current sharing host includes: If the current balancing host is not in bypass power supply, releasing the current balancing host; Alternatively, if a new cabinet is added to the parallel system, the current sharing host is released; Alternatively, if it is counted that there are multiple current-sharing hosts in the parallel system, the current-sharing host is released.

5. The method according to claim 1, characterized in that The current sharing slave realizes chopping by adjusting the conduction angle of the bypass SCR, including: Determine whether the current sharing slave needs to perform current sharing adjustment and obtain a fifth determination result; If the fifth judgment result is that the current sharing slave does not need to perform current sharing regulation, the SCR chopper of the current sharing slave is turned off.

6. The method according to claim 5, characterized in that If the fifth judgment result is that the current balancing slave needs to be current balancing adjusted, then when the effective value of the output current of the current balancing slave is greater than the average current output by the parallel system plus a set multiple of the rated output current of a single cabinet of the parallel system, the SCR chopper of the current balancing slave is forward regulated.

7. The method according to claim 5, characterized in that If the fifth judgment result is that the current balancing slave needs to be current balancing adjusted, then when the effective value of the output current of the current balancing slave is less than the average current output by the parallel system minus the set multiple of the rated output current of a single cabinet in the parallel system, the SCR chopping of the current balancing slave is reversely adjusted; otherwise, the SCR chopping of the current balancing slave is maintained.

8. The method according to claim 2, characterized in that: The determining whether the current sharing slave needs to perform current sharing adjustment and obtaining a fifth determination result includes: The output current of the parallel system is greater than a set multiple of the rated current, and the cabinet is not a current-sharing host, and the cabinet has no competing current-sharing host.

9. The method according to claim 6, characterized in that The SCR chopping forward regulation of the current sharing slave includes: If the current output of the current-sharing slave cabinet is greater than the effective value of the average current output by the parallel system, the conduction delay angle needs to be increased.

10. The method according to claim 7, characterized in that The SCR chopping reverse regulation of the current sharing slave includes: If the current output from the cabinet is less than the effective value of the average current output by the parallel system, the conduction delay angle needs to be reduced.

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