CA-3166051-C - APPARATUS AND METHOD FOR FLUX MANAGEMENT IN IMPEDANCE ISOLATION SINGLE CONVERSION (ZISC) BASED UPS SYSTEM

CA3166051CCA 3166051 CCA3166051 CCA 3166051CCA-3166051-C

Abstract

Embodiments of present disclosure relate to apparatus and method for flux management in the ZISC based UPS system. The apparatus comprises: a first determining unit configured to determine a first offset flux on a series reactor in the ZISC based UPS system when power quality events occur in a grid connected to the ZISC based UPS system and the ZISC based UPS system operates in a grid-connected mode; and a first resetting unit configured to provide synthetic impedance damping to the series reactor to reset the first offset flux.

Inventors

Sridhar Pulikanti
Simon Walton
Robert Turner
Nicholas James Elliott

Assignees

ABB SCHWEIZ AG

Dates

Publication Date: 20260505
Application Date: 20200109

Claims (1)

WE CLAIM: 1. An apparatus for flux management in an impedance isolation single conversion (ZISC) based uninterruptible power supply (UPS) system, the ZISC based UPS system comprising an input, an output, an input switch electrically coupled to the input of the ZISC based UPS system, an output switch electrically coupled to the output of the ZISC based UPS system, and a bypass switch coupled between the input and output of the ZISC based UPS system; the ZISC based UPS system further comprising a series reactor, a coupling transformer, a power conversion system and an energy storage, the series reactor being electrically coupled between the input switch and the output switch, the coupling transformer being electrically coupled to a node between the series reactor and the output switch, the power conversion system being electrically coupled to the coupling transformer, the energy storage being electrically coupled to the power conversion system; the ZISC based UPS system further comprising a system controller coupled to the input switch, the output switch, and the bypass switch and configured to regulate the power exchange between the ZISC based UPS system and a grid connected to the input of the ZISC based UPS system by operating the switches; the apparatus comprising: a first determining unit configured to determine a first offset flux on the series reactor in the ZISC based UPS system when power quality events occur in the grid and the ZISC based UPS system operates in a grid-connected mode; and a first resetting unit configured to provide synthetic impedance damping to the series reactor to reset the first offset flux. 13 Date Re1rue/Date Received 2024-02-09 2. The apparatus according to claim 1, further comprising: a second determining unit configured to determine a second offset flux on a transformer in the ZISC based UPS system when the ZISC based UPS system operates in the grid-connected mode or an island mode; and a second resetting unit configured to reset the second off set flux in response to a magnitude of the second offset flux exceeding a flux magnitude limit. 3. The apparatus according to claim 2, wherein the transformer is a coupling transformer or a downstream transformer. 4. The apparatus according to claim 2 or 3, wherein the second determining unit compnses: a voltage observer configured to determine a voltage on the transformer; and a flux estimator configured to estimate the second offset flux based on the determined voltage on the transformer and an intrinsic time constant term specific to the transformer. 5. The apparatus according to claim 4, wherein the voltage observer is further configured to: determine the voltage on the transformer based on a voltage at a terminal of a power conversion system in the ZISC based UPS system or an output voltage of the ZISC based UPS system. 6. The apparatus according to claim 4 or 5, wherein the second resetting unit compnses: a flux magnitude extractor configured to extract the magnitude of the second offset flux; a comparator configured to compare the magnitude of the second offset flux with the flux magnitude limit; a multiplier configured to multiply the second offset flux with a correction factor 14 Date Re1rue/Date Received 2024-02-09 in response to the magnitude of the second offset flux exceeding the flux magnitude limit to provide a compensation voltage; and a subtractor configured to subtract the compensation voltage from a target voltage reference to obtain a corrected voltage reference. 7. A method for flux management in an impedance isolation single conversion (ZISC) based uninterruptible power supply (UPS) system according to claim 1, the method comprising: determining a first offset flux on a series reactor in the ZISC based UPS system when power quality events occur in a grid connected to the ZISC based UPS system and the ZISC based UPS system operates in a grid-connected mode; and providing synthetic impedance damping to the series reactor to reset the first off set flux. 8. The method according to claim 7, further comprising: determining a second offset flux on a transformer in the ZISC based UPS system when the ZISC based UPS system operates in the grid-connected mode or an island mode; and in response to a magnitude of the second offset flux exceeding a flux magnitude limit, resetting the second offset flux. 9. The method according to claim 8, wherein the transformer is a coupling transformer or a downstream transformer. 10. The method according to claim 8 or 9, wherein determining the second offset flux comprises: determining a voltage on the transformer; and estimating the second offset flux based on the determined voltage on the transformer and an intrinsic time constant term specific to the transformer. Date Re1rue/Date Received 2024-02-09 11. The method according to claim 10, wherein determining the voltage on the transformer comprises: determining the voltage on the transformer based on a voltage at a terminal of a power conversion system in the ZISC based UPS system or an output voltage of the ZISC based UPS system. 12. The method according to claim 10 or 11, wherein resetting the second offset flux in response to the magnitude of the second offset flux exceeding the flux magnitude limit comprises: extracting the magnitude of the second offset flux; comparing the magnitude of the second offset flux with the flux magnitude limit; in response to the magnitude of the second offset flux exceeding the flux magnitude limit, multiplying the second offset flux with a correction factor to provide a compensation voltage; and subtracting the compensation voltage from a target voltage reference to obtain a corrected voltage reference. 16 Date Re1rue/Date Received 2024-02-09

Description

WO 2021/139891 PCT /EP2020/050459 APPARATUS AND METHOD FOR FLUX MANAGEMENT IN IMPEDANCE ISOLATION SINGLE CONVERSION (ZISC) BASED UPS SYSTEM FIELD [0001] Embodiments of the present disclosure generally relate to the field of power converter system, and more particularly, to apparatus and method for flux management in an impedance isolation single conversion (ZISC) based uninterruptible power supply (UPS) system. BACKGROUND [0002] Electrical or electronic equipment used in all types of industrial processes are vulnerable to power quality events in a grid. Power quality of the grid is related to variations in grid voltages in the form of momentary interruptions, voltage sags or swells, transients, harmonic distortion, electrical noise, and flickering lights, among others. In order to mitigate the effects of the power quality events and reduce the overall cost of customer continuous processes applications to make them more productive, efficient, and safe, one of the most common solutions is uninterruptible power supply (UPS). Different UPS systems have been developed targeting different customers. For example PCSI00 UPS aimed for industrial customers is an offline single conversion UPS system consisting of static switches, a power conversion system and an energy storage system. Recently a new architecture for the UPS system called as ZISC based UPS system is developed. The ZISC based UPS system is combination of components of the offline single conversion UPS and rotary UPS systems. [0003] In a steady-state grid-connected mode, when the grid is healthy, the ZISC based UPS system regulates its output voltage by exchanging power with the grid in order to compensate a voltage drop across a series reactor. In a case, when a voltage sag event occurs during the ZISC based UPS system operating in the grid-connected mode, a delta voltage across the series reactor leads to an offset flux. The offset flux on the series reactor may cause magnetic saturation of the series reactor, which results in a very high WO 2021/139891 PCT /EP2020/050459 current in a power conversion system and leads to a large distortion in the output voltage of the ZISC based UPS system. In another case, when the ZISC based UPS system operates in the grid-connected mode or an island mode, if a network feeder with downstream transformers is energised then it will results in flow of high inrush currents which may disturb the flux of a coupling transformer. In both cases, it will result in sympathetic saturation phenomena between the coupling transformer and downstream transformers, thus resulting in the distortion of the output voltage. Hence, the reliability of the ZISC based UPS system in protecting a customer load will be adversely effected. [0004] Thus, an offset flux resetting mechanism is required to improve the reliability and robustness of the ZISC based UPS system under above mentioned cases. SUMMARY [0005] In view of the foregoing problems, vanous example embodiments of the present disclosure provide apparatus and method for flux management in the ZISC based UPS system to avoid the magnetic saturation in the ZISC based UPS system. [0006] In a first aspect of the present disclosure, example embodiments of the present disclosure provide an apparatus for flux management in the ZISC based UPS system. The apparatus comprises: a first determining unit configured to determine a first offset flux on a series reactor in the ZISC based UPS system when power quality events occur in a grid connected to the ZISC based UPS system and the ZISC based UPS system operates in a grid-connected mode; and a first resetting unit configured to provide synthetic impedance damping to the series reactor to reset the first offset flux. [0007] In some embodiments, the apparatus further comprises: a second determining unit configured to determine a second offset flux on a transformer in the ZISC based UPS system when the ZISC based UPS system operates in the grid-connected mode or an island mode; and a second resetting unit configured to reset the second offset flux in response to a magnitude of the second offset flux exceeding a flux magnitude limit. [0008] In some embodiments, the transformer is a coupling transformer or a downstream transformer. 2 WO 2021/139891 PCT /EP2020/050459 [0009] In some embodiments, the second determining unit compnses: a voltage observer configured to determine a voltage on the transformer; and a flux estimator configured to estimate the second offset flux based on the determined voltage on the transformer and an intrinsic time constant term specific to the transformer. [0010] In some embodiments, the voltage observer is further configured to: determine the voltage on the transformer based on a voltage at a terminal of a power conversion system in the ZISC based UPS system or an output voltage of the ZISC based UPS system. [0011] In some embodiments, the second resetting unit comprises: a flux magnitude extractor configured to extract the ma