Analysis and Control of Modular Multilevel Converter With Split Energy Storage for Railway Traction Power Conditioner

Abstract

In this paper, a railway power conditioner (RPC) based on modular multilevel converter (MMC) with split supercapacitor energy storage system (SCESS) is studied. In this case, the MMC-SCESS based RPC could not only provide normal negative sequence currents (NSC) compensation but also could reduce the impact of power fluctuations caused by the locomotive braking or startup on the electric grid. Firstly, this paper analyzes the power flow patterns and deduces the reference circulating current under different operation modes of MMC-SCESS based RPC. Then, the control objectives of MMC-SCESS based RPC are divided into two categories including the balance control and the current tracking control. The balance control methods are developed for the submodules (SMs) capacitor voltages and the state of charge (SoC) of the supercapacitor, which are associated with the operation modes. To ensure the current tracking performance, a model predictive direct current control (MPDCC) method is presented for MMC and bidirectional energy converter (BEC). Finally, the effectiveness of the proposed control methods is verified by the experimental results of a downscaled prototype. Index Terms-Railway power conditioner (RPC), modular multilevel converter (MMC), split supercapacitor energy storage system (SCESS), power flow patterns, balance control, model predictive direct current control (MPDCC).

Control Design and Stability Analysis of Power Converters: The Discrete Generalized Bode Criterion

“…Most frequently, a constant feedback controller is selected, H(z) = K d , where K d is the damping constant and can be positive or negative [22], [59]. Thus, from (12) and (14), the open-transfer function becomes…”

“…The grid connection of renewable energy and Flexible AC Transmission Systems (FACTS) is growing steadily thanks to increasingly competitive costs [1]- [5]. The cost reduction is a result of a number of factors, which often create challenges with regard to the electronic converter control design and stability analysis, such as a reduction in component size [6]- [9], the use of high-power converters to benefit from economies of scale [10], [11], or the use of new topologies [12]- [14]. For this reason, a reliable tool which makes it possible to readily analyze the system stability is of the utmost importance.…”

Electromechanical transient modelling and application of modular multilevel converter with embedded energy storage

“…Other additional controllers are studied in [18][19][20], such as state-of-charge (SOC) controller, the DC power suppression controller, the harmonic currents controller etc. The application of MMC with embedded energy storage in medium-voltage electric drive as well as direct and indirect grid interfaces are discussed in [21][22][23].…”

Submodule power balancing control of modular multilevel converters under capacitor degradation

“…In recent times, modular multilevel converters (MMCs) have increased research attention due to the unique features of modularity, voltage scalability, fault‐tolerability, and potentiality to generate high power quality output waveforms [1, 2]. Owing to these pivotal characteristics, MMCs have triumphantly formed their way into commercial products in the areas of high‐voltage dc transmission, renewable energy integration, static compensator, railway traction systems, medium‐voltage motor drives, electric ship systems, and charging infrastructure for energy storage systems [2–9]. MMCs necessitate a complex control structure to effectuate the multiple control objectives such as output current control, capacitor voltage balancing (VB), inter‐arm voltage/energy balancing control, and circulating current (CC) suppression control [2, 3].…”