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The first 10-kV regional compensation dynamic voltage restorer (DVR) has been installed in a 110-kV substation in Shenzhen power grid, to protect plenty of sensitive loads in a wide area simultaneously from the disturbances caused by voltage sags. The location selection and performance indicators of the DVR are determined based on the voltage sag statistic results in recent years of Shenzhen power grid. The implementation schemes of main circuit elements, such as the energy storage unit, inverter and LC filter are presented. To further improve the DVR's cost-effectiveness, a novel virtual impedance control strategy is proposed to provide the DVR with a function of a Fault Current Limiter (FCL) or a Series Compensator (SC) besides the function of voltage sag compensation. Simulation and field experimental results are provided to show the correctness and effectiveness of the main circuit design and control system development of the 10-kV DVR. [ABSTRACT FROM AUTHOR]

Leg inductors which connect a shunt Active Power Filter (APF) to power network play a crucial role in guaranteeing desired performances of the APF. Optimal tuning of the inductances is still a tricky problem that has not yet been tackled systematically and theoretically. This paper proposes a novel inductance optimisation method that is universally applicable to four-wire shunt APFs with arbitrary topologies and PWM strategies. Based on the unified mathematic model, indexes used to quantitatively evaluate the abilities of a four-wire APF in compensating phase harmonic currents and depressing neutral line current are formally formulated. The upper and lower value constraints of the inductances are derived by comprehensively taking into account the characteristics of load harmonic profile and PWM strategy. Inductances are further optimised in the feasible value ranges with concern of several engineering application issues. Simulation and lab experiment results are provided to verify the validity and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The currently used hysteresis method is of low control accuracy, and the PWM-based strategy fails to provide a high enough response speed; thus, there is always a trade-off between the performances of control accuracy and response speed for a four-leg shunt active power filter (APF) to cope with the large variation in the load harmonic profile. First, an improved SVPWM strategy is proposed in this paper; with the aim to increase the response speed of a four-leg APF by simplifying the implementation of current 3D-SVPWM methods, the principle and realisation of this strategy are explained in detail. Based on these works, a compound PWM algorithm that effectively integrates the improved SVPWM and a PI-based current hysteresis method is proposed to simultaneously guarantee a higher response speed and a higher control accuracy for a four-leg APF. The realisation and parameter tuning of the compound PWM are elaborated. The correctness and effectiveness of the improved SVPWM and the compound PWM strategy are verified by simulations using Matlab/Simulink software. Finally, experimental results on a four-leg APF implemented in a closed-loop real-time simulation platform are presented. [ABSTRACT FROM AUTHOR]

A dynamic voltage restorer (DVR) can be installed in a middle-voltage (MV) power grid, to concurrently protect a cluster of sensitive loads from voltage sags. To further improve its efficiency and reduce the difficulty in its implementation, a novel control strategy for operating such a DVR as a virtual impedance in series with sensitive loads is proposed in this paper. In addition to its usual function of compensating for voltage sags, such a DVR can also operate as a virtual inductance, to function as a fault current limiter (FCL) during a downstream fault, or a virtual capacitance, to function as a series compensator (SC) to compensate the voltage loss along the feeder line during heavy load. Based on a dual-loop control design, strategies for operating a DVR as a series virtual inductance and a virtual capacitance are proposed, and methods for tuning the parameter values and a stability analysis of the whole system are presented. The feasibility and effectiveness of the proposed method are verified by simulations using the PSCAD software, and experimental results obtained using a prototype DVR are presented. [ABSTRACT FROM AUTHOR]

Online detuning state detection and the subsequent detuned element identification of a passive filter bank is of great concern in regard to achieving condition-based maintenance of an HVDC transmission system. In this paper, a novel method that can rapidly detect the online detuning state of filter banks with arbitrary structures of an HVDC system and accurately identify the detuning element is proposed. The method is based on the calculated amplitude change rates (ACRs) of several deliberately selected harmonic components of the measured real-time current in each branch of the filter. The principle and the implementation of the proposed method are presented, and the relationship between the ACR of the harmonic current and the detuning degree of an individual element is deduced theoretically. Based on the above works, the criteria for identifying the detuning state of the filter bank, the detuned element in the series and parallel part of the filter, and the detuning degree of the element are given. Diverse simulation results, such as applications on a single- and a double-tuned DC filter bank, sensitivity analysis and performance comparison, are provided to show the correctness and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper describes the design of a dynamic voltage restorer (DVR) that can simultaneously protect several sensitive loads from voltage sags in a region of an MV distribution network. A novel reference voltage calculation method based on zero-sequence voltage optimisation is proposed for this DVR to optimise cost-effectiveness in compensation of voltage sags with different characteristics in an ungrounded neutral system. Based on a detailed analysis of the characteristics of voltage sags caused by different types of faults and the effect of the wiring mode of the transformer on these characteristics, the optimisation target of the reference voltage calculation is presented with several constraints. The reference voltages under all types of voltage sags are calculated by optimising the zero-sequence component, which can reduce the degree of swell in the phase-to-ground voltage after compensation to the maximum extent and can improve the symmetry degree of the output voltages of the DVR, thereby effectively increasing the compensation ability. The validity and effectiveness of the proposed method are verified by simulation and experimental results. [ABSTRACT FROM PUBLISHER]