A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient volt...A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.展开更多
Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a signifi...Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.展开更多
This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the reg...This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the region below the rated wind speed. Gain scheduled control approach is applied in order to achieve high performance over a wide range of wind speed. A double loop configuration is adopted. In the inner loop, the rotor speed is used as the scheduling parameter, while a function of wind and rotor speed is used as the scheduling parameter in the outer loop. It is verified in simulations that a high tracking performance has been achieved.展开更多
The effects of parasitic capacitance in induction motor system are unnoticed when it is fed from the AC line, but they are obvious when supplied directly from a PWM inverter. Consequently, many parasitic problems occu...The effects of parasitic capacitance in induction motor system are unnoticed when it is fed from the AC line, but they are obvious when supplied directly from a PWM inverter. Consequently, many parasitic problems occur, such as motor to earth leakage current, bearing current, incoming line current distortion and uneven distribution of electrical stresses along the winding. On the basis of the uniform transmission line principle, a complete equivalent circuit of the PWM inverter fed motor system is presented, based on which all the capacitive parasitic problems mentioned above are analyzed and simulated by means of PSPICE. All the results are consistent with the existing ones.展开更多
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
基金supported by the National Natural Science Foundation of China(Grant No.51307124)the Major Program of the National Natural Science Foundation of China(Grant No.51190105)
文摘A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.
基金supported by State Key Laboratory of Power Transmission Equipment and System Security(No.2007DA10512711102,No.2007DA10512709202)Program of Introducing Talents of Discipline to Universities("111"Program)(No.B08036)the Fundamental Research Funds for the Central Universities(No.CDJXS11150026)
文摘Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.
文摘This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the region below the rated wind speed. Gain scheduled control approach is applied in order to achieve high performance over a wide range of wind speed. A double loop configuration is adopted. In the inner loop, the rotor speed is used as the scheduling parameter, while a function of wind and rotor speed is used as the scheduling parameter in the outer loop. It is verified in simulations that a high tracking performance has been achieved.
文摘The effects of parasitic capacitance in induction motor system are unnoticed when it is fed from the AC line, but they are obvious when supplied directly from a PWM inverter. Consequently, many parasitic problems occur, such as motor to earth leakage current, bearing current, incoming line current distortion and uneven distribution of electrical stresses along the winding. On the basis of the uniform transmission line principle, a complete equivalent circuit of the PWM inverter fed motor system is presented, based on which all the capacitive parasitic problems mentioned above are analyzed and simulated by means of PSPICE. All the results are consistent with the existing ones.
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。
