This paper presents a simulation study into the implementation of a modular multi-level flying capacitor converter as a STATCOM. The converter modulation scheme applied is based on Phase Shifted PWM and the two scenarios which require compensation are investigated to verify this topology. The two scenarios are PCC voltage regulation through reactive power compensation and power oscillation damping through reactive current compensation. Simulation results verify the performance of the chosen topology.
Adapting the conventional Space Vector modulation (SVM) scheme for modular multilevel cascaded converters is complicated as the number of switching vectors increases with the number of voltage levels. This paper introduces a novel SVM scheme that can be applied for the control of modular multilevel cascade converters (MMCC) with any number of levels. Instead of extending a single hexagon to the regions corresponding to the number of levels, the proposed method treats the three-phase MMCC as multiple inverters with a phase limb being a chain of basic three level H-bridge, five-level flying capacitor, or neutral point clamped inverters. Basic two or three level hexagons can be applied to determine the switch states and duty cycles separately within one tier of the converter and many such hexagons can be overlapped, with phase shift relative to each other, for the control of a complete MMCC. This approach simplifies the modulation algorithm and brings flexibility in shaping the output voltage waveforms for different applications. Simulation results confirm the good waveform performance of this scheme. An experimental 5-level MMCC, with a total of six H-bridges as the basic modules, is presented to validate the advantageous features of the method.
This paper presents a simulation study into the implementation of the single star flying capacitor converter modular multi-level cascaded converter (SSFCC-MMCC) as a STATCOM for unbalanced load compensation. The paper proposes a new concept of voltage source current control for the reference current tracking of the compensated currents. This control strategy enables the STATCOM system to compensate for both positive sequence reactive and negative sequence currents. Not only compensates for unbalanced load, but also keep the module Dc-link and flying capacitor voltages maintained at their rated values. Simulation results verify the performance of the chosen topology.
The rapid development and growth of battery storage have heightened an interest in the co-location of battery energy storage systems (BESS) with renewable energy projects which enables the stacking of multiple revenue streams while reducing connection charges of BESS. To help wind energy industries better understand the coordinated operation of BESS and wind farms and its associated profits, this paper develops a simulation model to implement a number of coordination strategies where the BESS supplies enhanced frequency response (EFR) service and enables the time shift of wind generation based on the UK perspective. The proposed model also simulates the degradation of Lithium-Ion battery and incorporates a state of charge (SOC) dependent limit on the charge rate derived from a constant current-constant voltage charging profile. In addition, a particle swarm optimisation-based battery sizing algorithm is developed here on the basis of the simulation model to determine the optimal size of the co-located BESS along with SOC-related strategy variables that maximise the net present value of the wind + BESS system at the end of the EFR contract.
The continuous development of hydrogen-electrolyser and fuel-cell technologies not only reduces their investment and operating costs but also improves their technical performance to meet fast-acting requirements of electrical grid balancing services such as frequency-response services. In order to project the feasibility of co-locating a hydrogen-storage system with a wind farm for the dynamic regulation frequency-response provision in Great Britain, this paper develops a modelling framework to coordinate the wind export and frequency responses to the main grid and manage the interaction of the electrolyser, compressor, storage tank and fuel cell within the hydrogen-storage system by respecting the market mechanisms and the balance and conversion of power and hydrogen flows. Then the revenue of frequency-response service provision and a variety of costs induced by the hydrogen-storage system are translated into the net profit of the co-location system, which is maximized by optimizing the capacities of hydrogen-storage-system components, hydrogen-storage levels that guide the hydrogen restoration via operational baselines and the power interchange between a wind-farm and hydrogen-storage system, as well as the capacities tendered for low- and high-frequency dynamic regulation services. The developed modelling framework is tested based on a particular 432-MW offshore wind farm in Great Britain combined with the techno-economics of electrolysers and fuel cells projected for 2030 and 2050 scenarios. The optimized system configuration and operation are compared between different operating scenarios and discussed alongside the prospect of applying hydrogen-storage systems for frequency-response provision.
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