Search

Fault current-limiting dynamic voltage restorers (FCL-DVRs), also named as dual-functional DVRs, involving both the FCL and the voltage compensation (VC) function, have attracted more attention. However, in case of the FCL-DVR operating in VC mode, either the high capacity of storage system in the dc-link or the oversizing of power converter is needed, and in case of the FCL-DVR operating in FCL mode both the high dc-link voltage and the oversizing of power converter are needed. Thus, in order to overcome these drawbacks, an improved FCL-DVR, which consists of an LC filter coupled with series coupling capacitor (LCC) at the ac side, is proposed in this article. The improved FCL-DVR using energy-optimized control strategy can not only perform the dual functions well, but also achieve the capacity optimization of FCL-DVR key components. The operating principle and performance of the proposed FCL-DVR under FCL and VC mode are elaborated, respectively. The optimal design of LCC and selection of FCL branch are studied in detail to ensure high stability and reliability for the proposed FCL-DVR operating in both modes. The simulation and experimental results clearly validate the effectiveness of the proposed topology and method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel bridge-type solid-state fault current limiter based on dynamic voltage restorer (BFCL-DVR). The new topology uses a DC-link in the back-to-back converter of DVR. The proposed BFCL-DVR is equivalent to the conventional DVR during normal operation mode. At fault inception, the controller deactivates the series converter IGBTs in faulty phase and activates the DC-link semiconductor switches, thus establishing an equivalent bridge-type current limiter to restrict the fault current. The magnitude of the fault current is adjustable by controlling the frequency and duty ratio of the semiconductor switch that is in parallel with the discharging resistance. Moreover, the device is able to quickly recover from the current limiting mode to the normal operation mode. In this study, the operation sequence, optimal value of discharging resistance, duty cycle, and frequency of semiconductor switches are obtained. The design methodology of the proposed BFCL-DVR is fully verified using PSCAD/EMTDC software. Experimental results validate the proposed topology and theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a combinational voltage booster technique for fault ride-through (FRT) capability enhancement of squirrel-cage induction generators (SCIGs) by a multifunctional series compensator (MFSC). This technique uses a couple of antiparallel thyristors across the ac terminals of a traditional dynamic voltage restorer (DVR). Two control schemes are applied: a DVR mode and a multifunctional mode. The MFSC can operate in the DVR mode to compensate the slight voltage fluctuations/imbalances at the point of common coupling (PCC). Also, when serious voltage sags occur in the line, the MFSC controller deactivates the faulty phase inverter and activates its corresponding thyristors to insert the equivalent impedance to maintain the voltage level during the fault. Then, it switches to DVR mode to improve the recovery time after the fault. An operational algorithm is applied to deal with different voltage sag depths caused by various fault conditions (both symmetrical and asymmetrical faults). Comprehensive simulations were carried out by using PSCAD/EMTDC software, and results show that the proposed technology is a very effective device to improve the FRT capability of the SCIG. A scaled-down experimental verification was carried out. Experimental results confirm the effectiveness of the combinational voltage booster technique of the MFSC for both slight and serious voltage sags. [ABSTRACT FROM AUTHOR]

Series-connected voltage sources converters (SVSCs), (i.e., dynamic voltage restorer, fault current limiter, electrical spring, etc.), have been widely used in the electricity grid to improve the electricity grid performances in terms of voltage fluctuation compensation, flexible power flow regulation, fault overcurrent limitation, flexible access of renewable energy, etc. However, SVSCs have a relatively short effective operating time and a low utilization rate, because they are generally operated during abnormal grid conditions. The new trend is to increase the utilization by extending the functions of SVSC, e.g., integrating the voltage compensation and overcurrent limiting in a single SVSC. On the other hand, the series connection architecture results in the SVSCs experiencing overvoltage and overcurrent from the main grid, and consequently the reliability of SVSC is challenged. Based on these details, this paper systematically studies the state of the art multifunctional techniques and the corresponding strategies of SVSCs, which can be mainly divided into three categories as follows: function integration between different SVSC; function coordination between SVSC and parallel-connected VSC(PVSC); function integration between SVSC and PVSC. The most representative topology and control optimization method in each category is elaborated, and a brief comparison of them is conducted as well. On this basis, the key problems and challenges in the research and engineering application of multifunctional SVSC system are summarized. • The state of the art multifunctional techniques of SVSCs is systematically studied. • The function coordination between SVSC and parallel-connected devices improves the output performance of the parallel part. • The multifunctional SVSC with fault current limiting capability can protect itself and the power grid actively. • The function integration between SVSC and PVSC open a new way to improve the utilization rate of power electronic devices. • The multifunctional SVSC with minimized additional physical switches and topology complexity needs further studied. [ABSTRACT FROM AUTHOR]