An uninterruptible power supply circuit and system for multiple frequency converters sharing a battery pack

Abstract

This utility model discloses an uninterruptible power supply circuit and system for multiple frequency converters sharing a battery pack, belonging to the field of frequency converter power supply technology. The uninterruptible power supply circuit for multiple frequency converters sharing a battery pack includes an AC power supply bus, a battery pack, and multiple frequency converter power supply branches; each branch is equipped with an independent three-phase rectifier bridge, a positive isolation diode, and a negative isolation diode. The three-phase rectifier bridge rectifies the AC power to supply power to the frequency converter; the positive and negative isolation diodes are connected in series between the battery pack and the branch input terminal, utilizing their unidirectional conductivity to achieve nanosecond-level zero-switching between AC power supply and battery pack power supply, without the need for a controller; multiple branches share a single battery pack, and the independent rectifier bridge and double-ended isolation diodes eliminate circulating current paths from the hardware topology. This utility model combines the beneficial effects of zero-switching anti-power fluctuation, cost reduction and efficiency improvement through multiple units sharing a battery pack, and enhanced safety by suppressing circulating current.

Description

Technical Field

[0001] This utility model belongs to the field of inverter power supply technology, specifically relating to an uninterruptible power supply circuit and system for multiple inverters sharing a battery pack. Background Technology

[0002] The statements herein provide only background information related to this invention and do not necessarily constitute prior art.

[0003] In the production processes of industries such as petrochemicals, biopharmaceuticals, metal smelting, and glass processing, when the AC power grid is interrupted or the voltage fluctuates (slight voltage), it may cause motor-driven power equipment to stop, leading to production interruptions, equipment damage, and serious economic losses.

[0004] To address these issues, existing technologies typically add a UPS or EPS power supply between the mains power and the frequency converter. These power supplies have an internal controller that, upon detecting a mains power anomaly, controls a switching device to switch to AC power converted from DC power from the battery for continued power supply. However, when the power supply is in standby mode, the switching time is generally on the order of seconds, and the frequency converter will still shut down. While the power supply can achieve zero-switching in case of mains power failure when in online mode, losses are significant, especially in industrial settings where considerable annual losses can occur. Furthermore, when multiple frequency converters are independently configured with battery banks, the number of devices is large, the footprint is large, and with a simple common bus, circulating currents can easily arise due to power differences or varying line impedances, threatening system safety. Utility Model Content

[0005] The purpose of this utility model is to overcome the shortcomings of the existing technology and provide an uninterruptible power supply circuit and system for multiple frequency converters sharing a battery pack. By proposing a pure hardware circuit structure with a backup mode, it directly supplies power to the frequency converters when the mains power is normal, without adding extra losses. When the mains power is abnormal, isolation diodes are used to achieve zero switching between AC power supply mode and battery pack power supply mode. At the same time, the independent rectification and double-ended isolation diode design ensure the anti-circulating current capability when multiple frequency converters share a battery pack.

[0006] To achieve the above objectives, this utility model is implemented through the following technical solution: On the one hand, the technical solution of this utility model provides an uninterruptible power supply circuit for multiple frequency converters sharing a battery pack, including: AC power supply bus, battery bank and multiple inverter power supply branches; each inverter power supply branch is equipped with a branch positive input terminal and a branch negative input terminal, which are respectively connected to the DC input positive terminal and DC input negative terminal of an inverter; each inverter power supply branch is equipped with a three-phase rectifier bridge, a positive isolation diode and a negative isolation diode; The AC input terminal of the three-phase rectifier bridge is connected to the three-phase line of the AC power supply bus, the DC output positive terminal is connected to the positive input terminal of the power supply branch of this inverter, and the DC output negative terminal is connected to the negative input terminal of the power supply branch of this inverter. The anode of the positive isolation diode is connected to the positive terminal of the battery pack, and the cathode is connected to the positive input terminal of the power supply branch of this inverter; the cathode of the negative isolation diode is connected to the negative terminal of the battery pack, and the anode is connected to the negative input terminal of the power supply branch of this inverter.

[0007] In at least one embodiment, each inverter power supply branch also includes an AC circuit breaker connected in series between the three-phase AC power grid and the AC input terminal of the three-phase rectifier bridge.

[0008] In at least one embodiment, each inverter power supply branch also includes a buffer contactor and a buffer resistor; the main contacts of the buffer contactor and the buffer resistor are connected in parallel and then connected in series between the positive DC output terminal of the three-phase rectifier bridge and the positive input terminal of the branch.

[0009] In at least one embodiment, each inverter power supply branch also includes a bus electrolytic capacitor bank and a bus discharge resistor; after the bus electrolytic capacitor bank and the bus discharge resistor are connected in parallel, one end is connected to the positive input terminal of the branch and the other end is connected to the negative input terminal of the branch.

[0010] In at least one embodiment, the bus electrolytic capacitor bank is composed of a first electrolytic capacitor and a second electrolytic capacitor connected in parallel, and the capacitance of the first electrolytic capacitor is smaller than the capacitance of the second electrolytic capacitor.

[0011] In at least one embodiment, the positive terminal of the battery pack is simultaneously connected to the anode of all positive isolation diodes in all inverter power supply branches; the negative terminal of the battery pack is simultaneously connected to the cathode of all negative isolation diodes in all inverter power supply branches.

[0012] In at least one embodiment, each inverter power supply branch further includes a DC circuit breaker; the positive terminal of the DC circuit breaker is connected in series between the cathode of the positive isolation diode and the positive input terminal of the branch, and the negative terminal of the DC circuit breaker is connected in series between the anode of the negative isolation diode and the negative input terminal of the branch.

[0013] In at least one embodiment, the positive isolation diode and the negative isolation diode are Schottky diodes.

[0014] On the other hand, the technical solution of this utility model also provides an uninterruptible power supply system for multiple frequency converters sharing a battery pack, including: multiple frequency converters, multiple electrical devices, and an uninterruptible power supply circuit for multiple frequency converters sharing a battery pack; wherein, the uninterruptible power supply circuit for multiple frequency converters sharing a battery pack includes: an AC power supply bus, a battery pack, and multiple frequency converter power supply branches; each frequency converter power supply branch is provided with a branch positive input terminal and a branch negative input terminal, which are respectively connected to the DC input positive terminal and DC input negative terminal of a frequency converter, and the AC output terminal of each frequency converter is connected to the power input terminal of an electrical device; Each inverter power supply branch is equipped with a three-phase rectifier bridge, a positive isolation diode, and a negative isolation diode; the AC input terminal of the three-phase rectifier bridge is connected to the three-phase line of the AC power supply bus, the DC output positive terminal is connected to the positive input terminal of the power supply branch of this inverter, and the DC output negative terminal is connected to the negative input terminal of the power supply branch of this inverter. The anode of the positive isolation diode is connected to the positive terminal of the battery pack, and the cathode is connected to the positive input terminal of the power supply branch of this inverter; the cathode of the negative isolation diode is connected to the negative terminal of the battery pack, and the anode is connected to the negative input terminal of the power supply branch of this inverter.

[0015] In at least one embodiment, it further includes: a backup frequency converter and its corresponding backup frequency converter power supply branch, the structure of the backup frequency converter power supply branch is the same as the structure of each frequency converter power supply branch, and the positive DC input terminal and the negative DC input terminal of the backup frequency converter are respectively connected to the positive input terminal and the negative input terminal of the backup frequency converter power supply branch.

[0016] The beneficial effects of the above-described technical solution of this utility model are as follows: This utility model discloses an uninterruptible power supply circuit for multiple frequency converters sharing a battery pack. By directly supplying power to the frequency converters after rectification of the AC power grid via an independent three-phase rectifier bridge, it avoids the losses and heat generation of the internal rectification stage of the frequency converter. Simultaneously, it utilizes the unidirectional conductivity of the positive and negative isolation diodes to achieve nanosecond-level natural zero-switching between AC power supply and battery pack power supply, without any controller intervention. This completely eliminates the risk of frequency converter undervoltage shutdown caused by control delays in traditional switching methods, effectively ensuring uninterrupted operation of frequency converter-driven equipment during power grid fluctuations. Furthermore, by simultaneously connecting the positive and negative terminals of a single battery pack in parallel to the entire system… The inverter power supply branch enables multiple inverters to share a single battery as a common backup power source, significantly reducing equipment procurement costs, minimizing battery cabinet space requirements, and simplifying power distribution wiring. Simultaneously, the independently connected positive and negative isolation diodes in each branch physically cut off the loop current path from a hardware topology perspective. This ensures that load changes, power differences, or line impedance fluctuations in any branch will not cause current backflow to other branches through the battery bank. Thus, while maintaining the economic efficiency of sharing battery resources, the problem of circulating current between multiple branches is completely eliminated, balancing the system's anti-power fluctuation reliability, operational safety, and engineering economy. Attached Figure Description

[0017] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments of this utility model and their descriptions are used to explain this utility model and do not constitute an improper limitation of this utility model.

[0018] Figure 1 This is a schematic diagram of an uninterruptible power supply circuit for a shared battery pack for multiple frequency converters, as disclosed in Embodiment 1 of this utility model.

[0019] The distances or dimensions between parts have been exaggerated to show their positions; the diagram is for illustrative purposes only. Detailed Implementation

[0020] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] For ease of description, the words "up," "down," "left," and "right" appearing in this utility model only indicate that they are consistent with the up, down, left, and right directions of the accompanying drawings. They do not limit the structure and are merely for the purpose of facilitating the description of this utility model and simplifying the description. They do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0022] Terminology Explanation: The terms "installation," "connection," "linking," and "fixing" in this utility model should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction relationship between two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.

[0023] Example 1 In one typical embodiment of this utility model, this embodiment discloses an uninterruptible power supply circuit for multiple frequency converters sharing a battery pack, including: an AC power supply bus, a battery pack, and multiple frequency converter power supply branches. Each frequency converter power supply branch is provided with a branch positive input terminal and a branch negative input terminal, which are respectively connected to the positive DC input terminal and the negative DC input terminal of a frequency converter.

[0024] Each inverter power supply branch includes a three-phase rectifier bridge, a positive isolation diode, and a negative isolation diode. The AC input of the three-phase rectifier bridge is connected to the three-phase AC power supply bus. The positive DC output of the three-phase rectifier bridge is connected to the positive input of this inverter power supply branch, and the negative DC output of the three-phase rectifier bridge is connected to the negative input of this inverter power supply branch. The anode of the positive isolation diode is connected to the positive terminal of the battery pack, and the cathode of the positive isolation diode is connected to the positive input of this inverter power supply branch. The cathode of the negative isolation diode is connected to the negative terminal of the battery pack, and the anode of the negative isolation diode is connected to the negative input of this inverter power supply branch.

[0025] Based on the above circuit structure, when the three-phase AC power grid is supplying power normally, the DC bus voltage output by the three-phase rectifier bridge is higher than the terminal voltage of the battery pack. The positive and negative isolation diodes are reverse-biased and cut off, and the AC power from the three-phase AC power grid is rectified into pulsating DC by the three-phase rectifier bridge to power the inverter. When the three-phase AC power grid is de-energized or the voltage drops to below the terminal voltage of the battery pack after rectification, the positive and negative isolation diodes are forward-biased and naturally conduct, and the battery pack provides seamless power to the inverter. When the three-phase AC power grid is restored, the rectifier bridge output voltage rises back to above the terminal voltage of the battery pack, and the positive and negative isolation diodes in each branch return to reverse bias and cut off, automatically switching the power supply back to the three-phase AC power grid. The entire switching process is automatically completed by the unidirectional conductivity of the isolation diodes, without the need for any controller intervention.

[0026] As a further implementation, each inverter power supply branch also includes an AC circuit breaker, which is connected in series between the three-phase AC power grid and the AC input terminal of the three-phase rectifier bridge to isolate power grid faults and control the AC power supply.

[0027] As a further implementation, each inverter power supply branch also includes a buffer contactor and a buffer resistor. The main contacts of the buffer contactor are connected in parallel with the buffer resistor, and then connected in series between the positive DC output terminal of the three-phase rectifier bridge and the positive input terminal of the branch. Initially, when the system is powered on, the buffer contactor contacts open, and the pulsating DC current output from the positive DC output terminal of the three-phase rectifier bridge charges the bus capacitor through the buffer resistor, limiting inrush current. After the bus voltage stabilizes, the buffer contactor contacts close, bypassing the buffer resistor to reduce circuit losses.

[0028] As a further implementation, each inverter power supply branch also includes a bus electrolytic capacitor bank and a bus discharge resistor. The bus electrolytic capacitor bank and the bus discharge resistor are connected in parallel, with one end connected to the positive input terminal of the branch and the other end connected to the negative input terminal. The bus electrolytic capacitor bank is used to stabilize the DC bus voltage and offset the effects of grid fluctuations or sudden load changes; the bus discharge resistor is used to release the energy stored in the capacitors when the system is powered off, preventing residual high voltage from damaging the inverter.

[0029] In a further embodiment, the bus electrolytic capacitor bank is composed of a first electrolytic capacitor and a second electrolytic capacitor connected in parallel, with the capacitance of the first electrolytic capacitor being smaller than that of the second electrolytic capacitor. The smaller-capacity first electrolytic capacitor is used to filter high-frequency ripple and limit the rate of current rise during the initial charging phase, while the larger-capacity second electrolytic capacitor is used to stabilize the DC bus voltage. In a further embodiment, the first electrolytic capacitor can be composed of multiple small-capacity electrolytic capacitors connected in series, and the second electrolytic capacitor can be composed of multiple large-capacity electrolytic capacitors connected in series.

[0030] As a further implementation, all inverter power supply branches share a single battery pack. Specifically, the positive terminal of the battery pack is simultaneously connected to the anode of all positive isolation diodes in all inverter power supply branches, and the negative terminal is simultaneously connected to the cathode of all negative isolation diodes in all inverter power supply branches. By connecting the positive and negative terminals of a single battery pack in parallel to all inverter power supply branches, all inverter branches share a single battery pack as a common backup power source. This achieves centralized configuration and shared use of the battery pack at the circuit structure level, significantly reducing equipment procurement costs, minimizing battery cabinet space requirements, and simplifying power distribution wiring. Simultaneously, since each branch has independent positive and negative isolation diodes, the discharge path from the battery pack to each branch is physically isolated by the unidirectional conduction characteristics of the diodes. Load changes, power differences, or line impedance fluctuations in any branch will not cause current backflow to other branches through the battery pack. Thus, while sharing the common resource of the battery pack, the hardware topology eliminates loop paths between multiple branches, balancing system economy and operational safety.

[0031] As a further implementation, each inverter power supply branch also includes a DC circuit breaker. The positive terminal of the DC circuit breaker is connected in series between the cathode of the positive isolation diode and the positive input terminal of the branch, and the negative terminal of the DC circuit breaker is connected in series between the anode of the negative isolation diode and the negative input terminal of the branch. This is used to cut off the discharge path of the battery pack when a DC-side short circuit occurs in the inverter, thereby protecting the battery pack from the impact of the DC-side short circuit.

[0032] As an alternative implementation, the positive and negative isolation diodes can be Schottky diodes, which have the characteristics of low forward voltage drop and extremely short reverse recovery time, which can further reduce conduction losses and shorten switching time.

[0033] As an example, such as Figure 1 As shown, an uninterruptible power supply circuit for multiple frequency converters sharing a battery bank includes: an AC power supply bus, a battery bank, and N frequency converter power supply branches, wherein... .

[0034] The three phases A, B, and C of the three-phase line of the AC power supply bus are respectively connected to AC circuit breakers. Three-phase rectifier bridges connected to the power supply branches of each frequency converter The AC input terminals (R / S / T) are composed of a three-phase rectifier bridge. Rectify three-phase alternating current into pulsating direct current. Three-phase rectifier bridge. The positive terminal of the DC output is connected to a buffer contactor. The main contacts are connected to the positive input terminal of the branch, and then to the positive DC input terminals L1, L2, and L3 of the strain gauge frequency converters 1~N; the three-phase rectifier bridge The negative terminal of the DC output is directly connected to the negative input terminal of the branch, and then connected to the negative DC input terminal R- of the frequency converter 1~N, which is the negative interface of the DC bus inside the frequency converter.

[0035] The positive terminal of the battery pack Simultaneously connect all positive isolation diodes in all N-channel inverter power supply branches anode, The cathodes are respectively connected to the positive input terminals of the power supply branches of each frequency converter; the negative terminal of the battery pack... Simultaneously connect all negative isolation diodes in all N-channel inverter power supply branches The cathode, The anodes are respectively connected to the negative input terminals of the power supply branches of each frequency converter.

[0036] Buffer resistor With buffer contactor After the main contacts are connected in parallel, they are connected in series with the three-phase rectifier bridge. Between the DC output positive terminal and the branch positive input terminal. The first electrolytic capacitor of the bus electrolytic capacitor bank. With the second electrolytic capacitor After being connected in parallel to form a busbar electrolytic capacitor bank, it is connected to the busbar discharge resistor. The capacitors are connected in parallel, with one end connected to the positive input terminal of the branch and the other end connected to the negative input terminal. The first electrolytic capacitor... This is a small-capacity capacitor, which can be composed of multiple small-capacity electrolytic capacitors connected in series, such as two 1000μF / 400V electrolytic capacitors connected in series; the second electrolytic capacitor... It is a large-capacity capacitor, which can be composed of multiple large-capacity electrolytic capacitors connected in series. For example, it can be composed of two 2200 μF / 400 V electrolytic capacitors connected in series, or two 4700 μF / 400 V electrolytic capacitors connected in series.

[0037] DC circuit breaker The positive terminal path is connected in series with the positive isolation diode. Between the cathode and the positive input terminal of the branch, the negative path is connected in series with the negative isolation diode. Between the anode and the negative input terminal of the branch.

[0038] The three AC input terminals L1, L2, and L3 of inverters 1 to N are shorted together to form the positive DC input terminal of the inverter, and the negative DC input terminal R- of the inverter forms the negative DC input terminal. Inverters 1 to N invert the DC bus voltage into three-phase AC power with adjustable frequency and voltage to drive the electrical equipment 1 to N (motor or pump).

[0039] After the system is powered on, close the AC circuit breaker. Three-phase alternating current is rectified by a three-phase rectifier bridge. The current is rectified into pulsating direct current and passed through a buffer resistor. Electrolytic capacitors for bus , And the inverter input unit is charged. After the bus voltage stabilizes, the buffer contactor... Closed bypass buffer resistor It enters main power supply mode.

[0040] During normal operation, the three-phase rectifier bridge The output DC bus voltage (e.g., approximately 540V after rectification of 380V AC) is higher than the battery pack terminal voltage (e.g., 535V). Positive isolation diode. The anode is connected to the positive terminal of the battery pack (potential approximately 535V), and the cathode is connected to the positive input terminal of the branch (potential approximately 540V). The cathode potential is higher than the anode potential. Reverse cutoff; negative isolation diode The cathode is connected to the negative terminal of the battery pack, and the anode is connected to the negative input terminal of the branch, also in reverse cutoff. The battery pack is in standby mode and does not supply power externally; the frequency converter is powered by the three-phase AC power grid through a three-phase rectifier bridge.

[0041] When the AC power grid experiences voltage dips (voltage drops or power outages), the three-phase rectifier bridge... The output DC bus voltage subsequently decreases. When the DC bus voltage drops below the battery pack terminal voltage (e.g., 535V), the positive isolation diode... The anode potential is higher than the cathode potential. Forward biased and naturally conducts; negative isolation diode The cathode potential is lower than the anode potential. Similarly, it conducts naturally when forward biased. and Seamlessly connected to the DC bus, providing continuous power to the frequency converter. The entire switching process is automatically completed by the unidirectional conductivity of the isolation diode, without any controller involvement. The switching time depends only on the response speed of the diode itself (≤100ns), achieving true zero-switching.

[0042] When the AC power grid is restored, the three-phase rectifier bridge The output DC bus voltage rises back above the battery pack terminal voltage, and the positive isolation diode... and negative isolation diode When reverse biased and naturally cut off, the battery pack automatically disconnects from power supply and switches back to AC grid power supply mode.

[0043] In scenarios where multiple frequency inverters share the same battery pack, each frequency inverter has an independent three-phase rectifier bridge. When the inverter power in a certain branch is high or the line impedance is different, due to the unidirectional conductivity of the rectifier diodes inside the three-phase rectifier bridge, that branch cannot reverse current into other branches. At the same time, independent isolation diodes are connected in series between the positive and negative terminals of the battery pack and each inverter power supply branch. and The battery pack current can only flow into the corresponding strain gauge through the isolation diode of this branch, and cannot be reverse-fed through the isolation diodes of other branches. The dual physical isolation design of the AC side and DC side completely blocks the circulating current path from the circuit topology.

[0044] In terms of reducing inverter losses, when a traditional inverter is connected to 380V AC power on the AC side, it needs to be converted to DC power through an internal rectifier bridge (e.g., 380V AC power rectified to approximately 537V DC). During this process, the input unit needs to withstand the positive and negative half-cycle impacts of the AC power, resulting in high current stress. The calculation formula is as follows:

[0045] In the formula, The power factor is typically taken as 0.8 to 0.9.

[0046] In the uninterruptible power supply circuit of this embodiment, the three-phase rectifier bridge The 380V AC mains power has been converted to 540V DC and directly connected to the input side of the frequency converter. The frequency converter does not require an internal rectifier bridge and only needs to handle a single DC bus. At this time, the input current is:

[0047] Because the DC voltage is constant, ,and , can be obtained Meanwhile, after shorting the three positive DC input terminals L1, L2, and L3 of the inverter, only one DC bus interface is needed internally, and the rectifier module power is:

[0048] Therefore, the input current and power of the frequency converter are significantly reduced, losses and heat generation are reduced, and the lifespan is extended.

[0049] In terms of anti-voltage fluctuation, traditional switching relies on the controller to detect the voltage drop in the grid → issue a switching command → the relay to act, which takes more than 10 ms. During the switching period, the bus voltage may be lower than the inverter's undervoltage protection value (such as 460 V), resulting in output interruption. In the uninterruptible power supply circuit of this embodiment, the large-capacity second electrolytic capacitor It can store sufficient energy: When the grid voltage fluctuates (e.g., drops from 380V to 370V for 500ms), the rectified bus voltage slowly decreases from 540V to 535V, matching the battery pack voltage. During this process, the second electrolytic capacitor... Discharge to maintain the bus voltage at no less than 460V, ensuring continuous operation of the inverter; if the grid voltage continues to drop below the inverter's AC low-voltage protection point (e.g., 323V), and the rectified bus voltage is below 535V, the positive isolation diode... The anode potential is higher than the cathode potential. Forward biased and naturally conducts; negative isolation diode The cathode potential is lower than the anode potential. Similarly, it conducts naturally under forward bias, with a conduction time not exceeding 20ns, ensuring seamless connection of the battery pack; after the grid is restored, the rectifier bus voltage rises to 540V, which is greater than the battery pack voltage of 535V, and the positive isolation diode... and negative isolation diode The reverse bias cutoff switches back to AC power, with a cutoff time not exceeding 100ns. The entire process is uncontrolled; the switching time is determined by the diode's response speed, requiring only nanoseconds, achieving "zero interruption."

[0050] Regarding the prevention of circulating current, when distributed multi-frequency converters share a common bus, if they share the same rectifier bridge or are only connected in parallel through conductors, current backflow may occur due to differences in power or line impedance, forming circulating current. The calculation formula is as follows:

[0051] In the formula, For branch voltage difference, This represents the line impedance.

[0052] In the uninterruptible power supply circuit of this embodiment, each frequency converter is equipped with an independent three-phase rectifier bridge. It contains 6 unidirectional conductive rectifier diodes to ensure that the output of the three-phase rectifier bridge supplies power only to this inverter. The three-phase rectifier bridges of other inverters cannot receive reverse current because the rectifier diodes are reverse cut off, thus achieving AC side anti-circulating current.

[0053] Meanwhile, each inverter is equipped with an independent positive isolation diode on both the positive and negative input sides. and negative isolation diode The battery pack current can only pass through the positive isolation diode of this inverter. and negative isolation diode The current flows in but cannot be reversed through the diodes of other frequency converters, thus achieving DC-side anti-circulating current.

[0054] The above-mentioned dual isolation design completely blocks the circulating current path from both the AC and DC sides, ensuring that multiple frequency converters can operate independently.

[0055] To verify the performance of the uninterruptible power supply circuit for a shared battery pack for multiple frequency converters proposed in this embodiment, key performance verification experiments were also conducted.

[0056] In terms of loss testing, the bus voltage after rectification from the 380V grid was 540V, which is 1.4 times higher than the traditional AC input, and the inverter input current was reduced to 0.7 times that of the traditional method. At the same time, the temperature rise of the inverter's rectifier module 1 decreased from 45 ℃ to 28 ℃, and the power of the input rectifier module decreased by 0.24 times.

[0057] In the zero-switching test, the grid voltage dropped to 370V for 500ms, and the rectifier bus voltage dropped to 530V, which is lower than the battery pack voltage of 535V. The positive and negative isolation diodes turned on within 20ns, and the inverter output was uninterrupted. After the grid was restored, the positive and negative isolation diodes turned off within 100ns, and the inverter switched back to AC power supply.

[0058] In the anti-circulating current test, when inverter 1 with a rated bus current of 14 A and inverter N with a rated bus current of 69 A share the same bus, the circulating current in the traditional solution reaches 2.1 A, which is about 15% of the rated current. However, the circulating current of the uninterruptible power supply circuit in this embodiment does not exceed 0.5 A, which is only 3.6% of the rated current.

[0059] Example 2 In one typical embodiment of this utility model, this embodiment discloses an uninterruptible power supply system for multiple frequency converters sharing a battery pack, including: multiple frequency converters, multiple electrical devices, and an uninterruptible power supply circuit for the multiple frequency converters sharing a battery pack. The uninterruptible power supply circuit for the multiple frequency converters sharing a battery pack includes: an AC power supply bus, a battery pack, and multiple frequency converter power supply branches; each frequency converter power supply branch has a positive input terminal and a negative input terminal, respectively connected to the positive and negative DC input terminals of one frequency converter, and the AC output terminal of each frequency converter is connected to the power input terminal of one electrical device.

[0060] Each inverter power supply branch includes a three-phase rectifier bridge, a positive isolation diode, and a negative isolation diode. The AC input of the three-phase rectifier bridge is connected to the three-phase AC power supply bus. The positive DC output of the three-phase rectifier bridge is connected to the positive input of this inverter power supply branch, and the negative DC output of the three-phase rectifier bridge is connected to the negative input of this inverter power supply branch. The anode of the positive isolation diode is connected to the positive terminal of the battery pack, and the cathode of the positive isolation diode is connected to the positive input of this inverter power supply branch. The cathode of the negative isolation diode is connected to the negative terminal of the battery pack, and the anode of the negative isolation diode is connected to the negative input of this inverter power supply branch.

[0061] Based on the aforementioned uninterruptible power supply circuit for multiple frequency converters sharing a battery pack, when the three-phase AC power grid is supplying power normally, the DC bus voltage output by the three-phase rectifier bridge is higher than the terminal voltage of the battery pack. The positive and negative isolation diodes are reverse-biased and cut off. The three-phase AC power grid is rectified into pulsating DC power by the three-phase rectifier bridge to power the frequency converters. The frequency converters then invert the DC power into frequency-adjustable three-phase AC power to drive the electrical equipment continuously. When the three-phase AC power grid is de-energized or the voltage drops to below the battery pack terminal voltage after rectification, the positive and negative isolation diodes are forward-biased and naturally conduct. The battery pack provides seamless power to the corresponding frequency converters, which continue to invert the DC power into three-phase AC power to drive the electrical equipment continuously. When the three-phase AC power grid is restored, the rectifier bridge output voltage rises back to above the battery pack terminal voltage. The positive and negative isolation diodes in each branch return to reverse bias and cut off, and the power supply automatically switches back to the three-phase AC power grid. The entire switching process is automatically completed by the unidirectional conductivity of the isolation diode without the need for any controller, ensuring that the power supply to the inverter-driven electrical equipment is uninterrupted and the operation continues uninterrupted during power grid fluctuations or outages.

[0062] As a further embodiment, an uninterruptible power supply circuit and system for multiple frequency converters sharing a battery pack also includes a backup frequency converter and its corresponding backup frequency converter power supply branch. The structure of the backup frequency converter power supply branch is the same as that of each frequency converter power supply branch. The positive and negative DC input terminals of the backup frequency converter are connected to the positive and negative input terminals of the backup frequency converter power supply branch, respectively. In the event of a main frequency converter failure, the backup frequency converter immediately takes over the power supply through corresponding positive and negative isolation diodes.

[0063] As a further implementation, each inverter power supply branch also includes an AC circuit breaker, which is connected in series between the three-phase AC power grid and the AC input terminal of the three-phase rectifier bridge to isolate power grid faults and control the AC power supply.

[0064] As a further implementation, each inverter power supply branch also includes a buffer contactor and a buffer resistor. The main contacts of the buffer contactor are connected in parallel with the buffer resistor, and then connected in series between the positive DC output terminal of the three-phase rectifier bridge and the positive input terminal of the branch. Initially, when the system is powered on, the buffer contactor contacts open, and the pulsating DC current output from the positive DC output terminal of the three-phase rectifier bridge charges the bus capacitor through the buffer resistor, limiting inrush current. After the bus voltage stabilizes, the buffer contactor contacts close, bypassing the buffer resistor to reduce circuit losses.

[0065] As a further implementation, each inverter power supply branch also includes a bus electrolytic capacitor bank and a bus discharge resistor. The bus electrolytic capacitor bank and the bus discharge resistor are connected in parallel, with one end connected to the positive input terminal of the branch and the other end connected to the negative input terminal. The bus electrolytic capacitor bank is used to stabilize the DC bus voltage and offset the effects of grid fluctuations or sudden load changes; the bus discharge resistor is used to release the energy stored in the capacitors when the system is powered off, preventing residual high voltage from damaging the inverter.

[0066] In a further embodiment, the bus electrolytic capacitor bank is composed of a first electrolytic capacitor and a second electrolytic capacitor connected in parallel, with the capacitance of the first electrolytic capacitor being smaller than that of the second electrolytic capacitor. The smaller-capacity first electrolytic capacitor is used to filter high-frequency ripple and limit the rate of current rise during the initial charging phase, while the larger-capacity second electrolytic capacitor is used to stabilize the DC bus voltage. In a further embodiment, the first electrolytic capacitor can be composed of multiple small-capacity electrolytic capacitors connected in series, and the second electrolytic capacitor can be composed of multiple large-capacity electrolytic capacitors connected in series.

[0067] As a further implementation, all inverter power supply branches share a single battery bank. Specifically, the positive terminal of the battery bank is simultaneously connected to the anode of all positive isolation diodes in all inverter power supply branches, and the negative terminal of the battery bank is simultaneously connected to the cathode of all negative isolation diodes in all inverter power supply branches. This parallel power supply using a single battery bank achieves cost and space efficiency. Simultaneously, the independently connected positive and negative isolation diodes in each branch physically disconnect the circulating current path, thus ensuring safe and non-interfering operation among multiple inverter branches while maintaining the economic efficiency of sharing battery resources.

[0068] As a further implementation, each inverter power supply branch also includes a DC circuit breaker. The positive terminal of the DC circuit breaker is connected in series between the cathode of the positive isolation diode and the positive input terminal of the branch, and the negative terminal of the DC circuit breaker is connected in series between the anode of the negative isolation diode and the negative input terminal of the branch. This is used to cut off the discharge path of the battery pack when a DC-side short circuit occurs in the inverter, thereby protecting the battery pack from the impact of the DC-side short circuit.

[0069] As an alternative implementation, the positive and negative isolation diodes can be Schottky diodes, which have the characteristics of low forward voltage drop and extremely short reverse recovery time, which can further reduce conduction losses and shorten switching time.

[0070] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. An uninterruptible power supply circuit for multiple frequency converters sharing a battery pack, characterized in that, include: AC power supply bus, battery bank and multiple inverter power supply branches; each inverter power supply branch is equipped with a branch positive input terminal and a branch negative input terminal, which are respectively connected to the DC input positive terminal and DC input negative terminal of an inverter; each inverter power supply branch is equipped with a three-phase rectifier bridge, a positive isolation diode and a negative isolation diode; The AC input terminal of the three-phase rectifier bridge is connected to the three-phase line of the AC power supply bus, the DC output positive terminal is connected to the positive input terminal of the power supply branch of this inverter, and the DC output negative terminal is connected to the negative input terminal of the power supply branch of this inverter. The anode of the positive isolation diode is connected to the positive terminal of the battery pack, and the cathode is connected to the positive input terminal of the power supply branch of this inverter; the cathode of the negative isolation diode is connected to the negative terminal of the battery pack, and the anode is connected to the negative input terminal of the power supply branch of this inverter.

2. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 1, characterized in that, Each inverter power supply branch also includes an AC circuit breaker, which is connected in series between the three-phase AC power grid and the AC input terminal of the three-phase rectifier bridge.

3. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 1, characterized in that, Each inverter power supply branch also includes a buffer contactor and a buffer resistor; the main contacts of the buffer contactor and the buffer resistor are connected in parallel and then connected in series between the positive DC output terminal of the three-phase rectifier bridge and the positive input terminal of the branch.

4. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 1, characterized in that, Each inverter power supply branch also includes a bus electrolytic capacitor bank and a bus discharge resistor; after the bus electrolytic capacitor bank and the bus discharge resistor are connected in parallel, one end is connected to the positive input terminal of the branch and the other end is connected to the negative input terminal of the branch.

5. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 4, characterized in that, The bus electrolytic capacitor bank is composed of a first electrolytic capacitor and a second electrolytic capacitor connected in parallel, and the capacitance of the first electrolytic capacitor is smaller than the capacitance of the second electrolytic capacitor.

6. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 1, characterized in that, The positive terminal of the battery pack is simultaneously connected to the anode of all positive isolation diodes in all inverter power supply branches; the negative terminal of the battery pack is simultaneously connected to the cathode of all negative isolation diodes in all inverter power supply branches.

7. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 1, characterized in that, Each inverter power supply branch also includes a DC circuit breaker; the positive path of the DC circuit breaker is connected in series between the cathode of the positive isolation diode and the positive input terminal of the branch, and the negative path of the DC circuit breaker is connected in series between the anode of the negative isolation diode and the negative input terminal of the branch.

8. The uninterruptible power supply circuit for a shared battery pack for multiple frequency converters as described in claim 1, characterized in that, Both the positive and negative isolation diodes are Schottky diodes.

9. An uninterruptible power supply system for multiple frequency converters sharing a battery pack, characterized in that, include: An uninterruptible power supply circuit for multiple frequency converters, multiple electrical devices, and a shared battery pack for multiple frequency converters is provided. The uninterruptible power supply circuit for multiple frequency converters includes: an AC power supply bus, a battery pack, and multiple frequency converter power supply branches. Each frequency converter power supply branch is provided with a positive input terminal and a negative input terminal, which are respectively connected to the positive DC input terminal and the negative DC input terminal of a frequency converter. The AC output terminal of each frequency converter is connected to the power input terminal of a piece of electrical equipment. Each inverter power supply branch is equipped with a three-phase rectifier bridge, a positive isolation diode, and a negative isolation diode; the AC input terminal of the three-phase rectifier bridge is connected to the three-phase line of the AC power supply bus, the DC output positive terminal is connected to the positive input terminal of the power supply branch of this inverter, and the DC output negative terminal is connected to the negative input terminal of the power supply branch of this inverter. The anode of the positive isolation diode is connected to the positive terminal of the battery pack, and the cathode is connected to the positive input terminal of the power supply branch of this inverter; the cathode of the negative isolation diode is connected to the negative terminal of the battery pack, and the anode is connected to the negative input terminal of the power supply branch of this inverter.

10. The uninterruptible power supply system for multiple frequency converters sharing a battery pack as described in claim 9, characterized in that, Also includes: A standby frequency converter and its corresponding standby frequency converter power supply branch. The structure of the standby frequency converter power supply branch is the same as that of each frequency converter power supply branch. The positive and negative DC input terminals of the standby frequency converter are connected to the positive and negative input terminals of the standby frequency converter power supply branch, respectively.

Images