The accurate information of the wide-bandwidth impedance versus the frequency is urgently needed for evaluating the system resonances, instabilities, and operations of the railway traction power system (TPS), and to avoid/control the harmonic resonance and oscillation issues. As the system topology and detailed parameters of the TPS are not fully known even timely varying, we have to obtain the detailed wide-bandwidth impedance information through exciting the harmonic disturbance into the system, and then, calculating the response information. Therefore, a controlled wide-bandwidth impedance measurement approach is presented in this paper, in which, a butterfly-type disturbance circuit and chirp pulsewidth modulation signal model are incorporated to generate the desired controlled-bandwidth harmonics with a high aggregation as well as the average amplitude. Impedance measurement results of the proposed approach have been validated through both simulation and experiment. Considering the measured errors, the proposed method is efficient in testing the wide-bandwidth impedance of the single-phase railway traction system.

Instability and oscillation issues have frequently occurred in high-speed railways due to the impedance mismatch versus frequency between the four-quadrant converter (4QC)-based high-speed train and the traction network (hereinafter train-network). However, solely utilizing the mathematical deduction to quantify the impedances seems to be difficult owing to unknown detailed parameters of both traction network and electric train. This paper proposes a method to measure the equivalent impedances of the traction network and the 4QC of the electric train in the stationary frame for stability analysis. A disturbance circuit consisting of antiparallel insulated gate bipolar transistor (IGBT) modules and an excitation load is adopted by means of the pulsewidth modulation (PWM) signal to drive the IGBTs. Consequently, a desired broad spectral excitation is then generated to measure the output impedance of the traction network. When injecting the harmonics twice, which are linearly independent at the same frequency, the input impedance of the 4QC can be calculated at the corresponding frequency considering the frequency-coupled effect. The proposed method shows a good measurement accuracy. Additionally, the stability and oscillation issues of the train-network system can be then identified using measured impedances. Both simulation and experimental results validate the effectiveness of the proposed measurement method.

The traditional model-based energy management strategy (EMS) for regenerative braking energy storage systems (RBESS) is obsoleting in the face of increasingly complex and un-certain operation conditions in railway power system (RPS). In this paper, a model-free deep reinforcement learning (DRL) method is proposed. First, the multi-objective energy manage-ment problem for RBESS is formulated to concurrently achieve the RBE utilization and power demand shaving of RPS. Then, this problem is modeled as a Markov decision process (MDP) to be solved by the DRL-based method. Specifically, the RBESS con-troller is modeled as an agent to interact with the environment modeled as the RPS integrated with RBESS. To coordinate the agent to learn the optimal strategies regarding multiple energy management objectives in different time scales, a multistage reward function involving the step reward and final reward is de-signed. Based on the above elements, the double deep Q-learning algorithm is applied to train the agent for optimizing the EMS. Finally, the proposed DRL-based EMS is tested on the OPAL-RT experimental platform by using the field load data. Case studies have demonstrated that the proposed method outperforms the traditional rule-based and optimization-based methods by over 5% in the energy management objective.

Railway traction power system (TPS) impedance affects the stability and operation performance of connected power electronics devices (i.e., electric trains) with the closed-loop control system. In order to identify the detailed TPS impedance, the wideband-response-based impedance measurement technique has become attractive for its fast execution time and accuracy, especially the chirp-based technique for its bilateral controllability of injected wideband disturbance. However, for the reason that the disturbance device is directly powered by the measured system, the fundamental component separates some harmonic clusters in the frequency domain and leads to unsatisfactory uniformity of the injected wideband disturbance. In this article, a segmented-chirp-based technique is proposed to eliminate this phenomenon caused by the fundamental component, where the chirp signal is segmented and carried on the fundamental only when the amplitude is relatively smooth on top (or bottom), which facilitates a uniform wideband distribution to keep a good measurement accuracy. Meanwhile, the presented modular disturbance circuit with a flexible topology can better adapt to the various industrial engineering conditions. Finally, the detailed measurement results based on the simulation and downscaled experimental system validate the effectiveness of the proposed measurement scheme.

Wideband impedances of the single-phase four-quadrant converter (4QC)-based high-speed train are of great significance for small-signal stability analysis in the electric railway system. However, the conventional impedance measurement strategy relies on sweeping the desired frequencies repeatedly that extremely slows down the impedance measurement speed, which, usually, seems incapable for the actual dynamic industrial systems. Addressing this shortcoming, this article proposes a novel impedance measurement approach based on the wideband excitation to greatly enhance its rapidity. Further, to eliminate the frequency overlapping effects under the wideband excitation, the proposed alternate injection strategy realized by the multitone signal can separate the effective frequencies from the coupling frequencies in the $\alpha \beta $ frame. Afterward, the dq -frame data covering all the desired frequencies can be obtained by combining the conventional method and the proposed $\alpha \beta $ -value exchange method ( $\alpha \beta $ -VEM), which can be applied for the impedance calculation. Finally, the results of both simulation and real-time hardware-in-the-loop (HIL) tests can well verify the effectiveness of the proposed approach.

The accurate dq -frame impedance of three-phase grid is essential in the stability analysis of grid-connected VSC system. However, the conventional measurement methods relying on two separate independent injections extremely slow down the impedance measurement speed, lacking adaptability for the actual dynamic industrial grid. To address this shortcoming, this paper proposes a rapid dq -frame impedance measurement approach for three-phase grid. In this approach, only one injection of wideband harmonics is needed so that the injection times can be reduced to half of the conventional methods and then the measurement time is shortened by half, dramatically enhancing the real-time performance of measurement result. Firstly, an interphase QAM multitone current injection method is proposed, which can excite the first group of desired wideband responses through a single injection. Then, a fictitious disturbance excitation method is introduced to substitute for the second injection of actual disturbance, which can construct the second group of wideband responses by rotation transformation. Afterward, the wideband dq -frame impedance can be calculated with these two groups of response data. The feasibility and effectiveness of the proposed approach are validated by both simulation and experiment results.