Abstract
This paper presents a deadbeat predictive current control methodology to reduce the circulating currents in a modular multilevel converter (MMC) when it operates as a rail power conditioner (RPC) in a conventional railway system-based V/V connection. For this purpose, a half-bridge MMC based on half-bridge submodules, operating as an RPC is explained, and the total system is denominated as a simplified rail power conditioner (SRPC). The SRPC in this study is used to compensate harmonics, reactive power, and the negative sequence component of currents. This paper explains the SRPC system architecture, the key control algorithms, and the deadbeat predictive current control methodology. Mathematical analysis, based on the MMC equivalent circuit, is described and the reference equations are presented. Moreover, simulation results of the deadbeat predictive current control methodology are compared with the results of the conventional proportional-integral (PI) controller. This comparison is to verify the effectiveness of the proposed control strategy. Simulation results of the SRPC show reduced circulating currents in the MMC phases when using the predictive control approach, besides accomplishing power quality improvement at the three-phase power grid side.
Highlights
Power quality phenomena in alternating current (AC) electrified railway have drawn more attention in the last decades, especially, after the evolution in the power electronics field [1]
By taking into consideration twenty-four SMs in each modular multilevel converter (MMC) leg, so the total SMs number will be divided between the upper and the lower arms in the same phase leg, the arm will consist of twelve SMs (N = 13, Thirteen-levels MMC)
An MMC with a few levels is sufficient for a proof-of-concept of the deadbeat predictive current control, the simulation model of the simplified rail power conditioner (SRPC) consists of twenty-four SMs per each leg (13-levels), and it was developed under PSIM v9.1 simulation tool, where the main parameters are presented in Tables 1 and 2
Summary
Power quality phenomena in alternating current (AC) electrified railway have drawn more attention in the last decades, especially, after the evolution in the power electronics field [1]. This method does not eliminate all the even-order harmonics in the MMC arm currents In this context, a methodology using the deadbeat predictive current control to reduce the MMC circulating currents is presented in this paper, bearing in mind that, the interrelation between the MMC output currents, the MMC circulating currents, and the SM voltages complicates the MMC control. The more accurate the parameter values of the SRPC model, the better the performance of the controller In this framework, the main contributions of this paper are: (a) Proposing a methodology based on a deadbeat predictive current control for the circulating current suppression in MMC; (b) An ample mathematical analysis of the SRPC equivalent circuit to extract the final reference equations; (c) A comprehensive comparison between the deadbeat predictive current control methodology and the conventional PI control approach.
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