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With the rapid development of high-speed and high-power railway system in China, power quality such as the negative sequence current and harmonic current caused by electric locomotives becomes more and more critical. This paper proposes a half-bridge-converter-based railway static power conditioner (RPC) (HBRPC) which consists of two half-bridge converters connected by two capacitors in series. Compared with the traditional RPC, the HBRPC requires only a pair of power switch legs and two capacitors. Under the premise of accomplishing the same function of RPC, the proposed conditioner can reduce half of the power switches, which can make it with lower cost and hardware complexity. A double-loop control is proposed for HBRPC to keep the dc-link voltage stable and achieve the dynamic tracking of the current reference signals, while a balanced voltage control is proposed to eliminate the error of two capacitor voltages and maintain the normal operation of HBRPC. Finally, simulation and experiment results have verified the proposed structure and its control method effectively. [ABSTRACT FROM PUBLISHER]

The Shangdu power plant has four 600-MW turbine-generators connected to the North-China Grid through two 500-kV transmissions, which are compensated with 45% fixed series capacitors. Extensive studies conducted on the system model indicate that the system suffers from multimodal subsynchronous resonance (SSR). To solve the problem, a countermeasure is developed by combining the supplementary excitation damping control (SEDC) and the torsional stress relay (TSR). In this paper, the characteristics of the SSR problem are investigated. Then the developed SEDC is presented. To validate the effectiveness of the proposed SEDC as well as the results of model studies, field tests were conducted under various operating conditions. The tests fully exposed the realistic threat of SSR in the system. Meanwhile, it is demonstrated that the developed SEDC can improve torsional damping significantly, and thus solve the multimodal SSR problem effectively. This is the first time in China that practical SEDCs have been developed and their ability to mitigate multimodal SSR has been verified in a real series-compensated system. [ABSTRACT FROM AUTHOR]

This article introduces the measurement and analysis of the transient electric field (E-field) derived from the switching operation of the modular multilevel converter (MMC) and the high voltage direct current (HVdc) circuit breaker (CB) in a 200 kV converter station constructed in the Zhoushan Islands, China. It is revealed that the switching transient E-field in the converter station is a quasi-static field. Although the switching E-field pulse is a kind of electromagnetic interference to the secondary electronic circuit of the converter station, it can be used to accurately monitor the action moment of the MMC and the CB. The action moment of the MMC and the CB can be measured with an error of less than 0.005 ms based on the steep pulse front of the switching E-field pulse. This result, which is far more accurate compared to the measurement using the voltage recording system that comes with the converter station. This is of significance to the relay protection of the HVdc transmission system whose fault rapidly develops. Additionally, this method has the advantage of being noninvasive, flexible, and low cost. It has potential application value in the condition monitoring of the MMC and the HVdc CB. [ABSTRACT FROM AUTHOR]

Three-phase unbalance could have significant impacts on the secure and economic operation of a low-voltage distribution system. With the deployment of smart meters and the emergence of phase switch devices (PSDs), more efficient schemes for mitigating three-phase unbalance are expected by utilizing numerous measurement data and the installed PSDs in low-voltage areas. Therefore, a bi-level optimal phase switch device placement model for mitigating three-phase unbalance is proposed in this work. In the upper-level model, the PSD placement strategy is optimized by minimizing the total costs of PSD installation and operation costs of low-voltage areas determined in the lower-level model. In the lower-level model, the operation costs of low-voltage areas for typical days are minimized based on the PSDs and their locations determined in the upper-level model. The proposed bi-level model is tested by an actual low-voltage area of Zhejiang province, China, and the effectiveness of the optimal PSD placement model for reducing the total investment and operation costs of the low-voltage area demonstrated. [ABSTRACT FROM AUTHOR]