随着电力电子技术的快速发展,直流概念在输配电以及新能源汇聚中的技术优势日益显现。用以匹配不同电压等级和接入直流设备,直流变压器是直流电网中的关键设备。将现有高效且可靠的隔离性双有源桥变换器(dual active bridge,DAB)中单开...随着电力电子技术的快速发展,直流概念在输配电以及新能源汇聚中的技术优势日益显现。用以匹配不同电压等级和接入直流设备,直流变压器是直流电网中的关键设备。将现有高效且可靠的隔离性双有源桥变换器(dual active bridge,DAB)中单开关扩展为子模块串联链,构建MMC直流变压器(modular multilevel converter based DC transformer,MMC-DCT),进一步采用准两电平调制以综合DAB和MMC优势,是满足直流电网需求的有效方案。然而,新能源接入对MMC-DCT的电压灵活度提出了新的要求。从直流侧看,MMC通常作为电压源变换器使用,当MMC-DCT的直流电压比与变压器变比不匹配时,交流侧无功和电流应力增加,导致效率降低。为克服MMC-DCT的上述缺陷,扩展电压灵活性,通过将MMC桥臂电感改为耦合电感,该文提出了MMC-DCT电流源运行模式,随着直流电压变化,所提出的控制算法可以维持子模块电压应力不变。同时,电流源运行增加了交流侧近似方波电压的上升和下降边沿阶梯数,进一步降低du/dt和隔离变绝缘应力。仿真和实验结果验证了所提电流源运行方式的有效性。展开更多
The reliability of electric supply to consumers is one of the most important factors that determine the requirements imposed on modem utility companies. This paper presents the results of investigation by computer sof...The reliability of electric supply to consumers is one of the most important factors that determine the requirements imposed on modem utility companies. This paper presents the results of investigation by computer software of the overvoltages resulting from a ferroresonance conditions in MV networks at open phase operating condition with and without connection to earth on source and load sides of distribution transformer. This overvoltage may reach 4.2 pu on one of the HV side of transformer unswitched phases. The results of the study show that ferroresonance overvoltage may be controlled by replacing fuses with circuit breakers on HV side to ensure switching-off all phases. Insertion of resistor or reactor in the neutral of source and loadsides of the transformer with 5% active load will help in suppressing overvoltages.展开更多
文摘随着电力电子技术的快速发展,直流概念在输配电以及新能源汇聚中的技术优势日益显现。用以匹配不同电压等级和接入直流设备,直流变压器是直流电网中的关键设备。将现有高效且可靠的隔离性双有源桥变换器(dual active bridge,DAB)中单开关扩展为子模块串联链,构建MMC直流变压器(modular multilevel converter based DC transformer,MMC-DCT),进一步采用准两电平调制以综合DAB和MMC优势,是满足直流电网需求的有效方案。然而,新能源接入对MMC-DCT的电压灵活度提出了新的要求。从直流侧看,MMC通常作为电压源变换器使用,当MMC-DCT的直流电压比与变压器变比不匹配时,交流侧无功和电流应力增加,导致效率降低。为克服MMC-DCT的上述缺陷,扩展电压灵活性,通过将MMC桥臂电感改为耦合电感,该文提出了MMC-DCT电流源运行模式,随着直流电压变化,所提出的控制算法可以维持子模块电压应力不变。同时,电流源运行增加了交流侧近似方波电压的上升和下降边沿阶梯数,进一步降低du/dt和隔离变绝缘应力。仿真和实验结果验证了所提电流源运行方式的有效性。
文摘The reliability of electric supply to consumers is one of the most important factors that determine the requirements imposed on modem utility companies. This paper presents the results of investigation by computer software of the overvoltages resulting from a ferroresonance conditions in MV networks at open phase operating condition with and without connection to earth on source and load sides of distribution transformer. This overvoltage may reach 4.2 pu on one of the HV side of transformer unswitched phases. The results of the study show that ferroresonance overvoltage may be controlled by replacing fuses with circuit breakers on HV side to ensure switching-off all phases. Insertion of resistor or reactor in the neutral of source and loadsides of the transformer with 5% active load will help in suppressing overvoltages.