A Delta-Connected Modular Multilevel STATCOM With Partially-Rated Energy Storage for Provision of Ancillary Services

Abstract

This paper proposes a delta-connected Modular Multilevel STATCOM with partially rated storage (PRS-STATCOM), capable of providing both reactive and active power support. The purpose is to provide short-term energy storage enabled grid support services such as inertial and frequency response, either alongside or temporarily instead of standard STATCOM voltage support. The topology proposed here contains two types of sub-modules (SM) in each phase-leg: standard submodules (STD-SMs) and energy storage element sub-modules (ESE-SMs) with a dc-dc interface converter between the SM capacitor and the ESE. A control structure has been developed that allows energy transfer between the SM capacitor and the ESE resulting in active power exchange between the converter and the grid. Injecting 3 rd harmonic current into the converter waveforms can be used to increase the amount of power that can be extracted from the ESE-SMs and so reduce the required ESE-SMs fraction in each phase-leg. Simulation results demonstrate that for three selected active power ratings, 1 pu, 2 3 pu, & 1 3 pu, the fraction of SMs that need be converted to ESE-SMs are only 69%, 59% & 38%. Thus, the proposed topology is effective in adding real power capability to a STATCOM without a large increase in equipment cost.

Delta Configured Multi Busbar Sub-Module Modular Multilevel STATCOM With Partially Rated Energy Storage for Frequency Support

“…The capacitor voltage deviation will also be increased accordingly since capacitors in normal MBSMs are not affected by the ES current raise. A normally used solution for reducing the voltage deviation is injecting additional third harmonic circulating current I 3rd [13], [14]. The total stack current reference I S ref is calculated by the sum of phase current that contribute to AC output I ph , I 0 , and I 3rd .…”

“…active power as introduced before. The amplitude of I 3rd should also ensure that the peak stack current does not exceed 1 p.u., as suggested in [13], [28]. With the system parameters listed in Table II, the maximum amplitude of total stack current is 962A, and the maximum amplitude of I 3rd can be injected is 394A.…”

“…The MMC with partially rated integrated ES and its control system proposed in [12] is suitable for frequency support and ancillary service provision such as decoupled power oscillation damping. In [13], the partially rated energy storage (PRES)-STATCOM capable of providing both reactive and active power support and voltage balancing algorithm are introduced together. Fig.…”

A Comprehensive Review on STATCOM: Paradigm of Modeling, Control, Stability, Optimal Location, Integration, Application, and Installation

“…The effectiveness is tested for balanced and unbalanced conditions. A multi-bus bar sub-module for STATCOM with partially rated energy storage is explained in [6]. The module is better at maintaining frequency within the limit and reactive power compensation in comparison to a conventional full-bridge submodule.…”

Design of a linearized 4-H-bridge STATCOM for load balancing purposes

“…Disturbances like the fluctuations of voltage resulting from the complexities of grid and conditions of unbalanced loads cause severe power quality issues like voltage unbalance and total harmonic distortion [21]. A delta-connected Multilevel STATCOM was proposed to provide both Var and real power support [22]. The purpose of this work was to accomplish short-term storage of energy to enable grid support services.…”