Repair based Constraint Handling Techniques for Microgrid Sizing and Energy Management Optimisation


Microgrid sizing and energy management system (EMS) optimisation problems have conflicting objectives while subjected to complex constraints. These problems are usually solved by using meta-heuristic algorithms, which are originally developed to solve unconstrained problems. Therefore, appropriate constraint handling technique (CHT) must be employed to solve constrained problems. It appears that use of CHTs in these problems is rare. This study proposes using two types of repair-based penalty approaches to solve a microgrid sizing and EMS problem. Cuckoo search algorithm is employed to solve the multi-objective optimisation problem, which minimises the levilised cost of electricity (LCOE) and dump load, while maximising the reliability of power supply. A case study based on the Westray Island standalone microgrid in Scotland is conducted to compare the effectiveness of the repair approaches, in terms of the objective function values and convergence speed.

Keywords: Constraint handling, Energy management system, Microgrid, Renewables, Repair methods, Sizing

Impact of Wave Energy Integration on Sizing and Energy Management of a Microgrid: Case study


This paper investigates the impact of integrating a wave energy converter (WEC) on sizing the battery and energy management of a microgrid utilising wind, solar and diesel generator at the generation side. A sequential co-optimisation model for sizing and energy management is proposed to minimise the levilised cost of electricity (LCOE) and dump load, while maximising the reliability of power supply. Cuckoo search algorithm is employed to solve the multi-objective optimisation problem. Moreover, a repair-based penalty approach is integrated for effective constraint handling. The Westray Island standalone microgrid in Scotland is considered as a case study. Annual hourly weather data of Westray Island and the demand profile are used to simulate the system in MATLAB environment. The numerical results show that the battery capacity is reduced when WEC is integrated in the microgrid. However, with the WEC integration, the LECO slightly increases with increased reliability of the power supply.

Keywords: Constraint handling, Energy management system, Microgrid, Sizing, Wave energy



Study of a DC Micro-Gird Configuration to Produce Hydrogen (DCMG-H2)

The configuration of a cutting-edge DC Micro-Grid system to produce Hydrogen (DCMG-H2) from Renewable Energy Sources (RESs) is described.

This analysis clearly highlights the unnecessary power conversions in an ACMG in practice when the system can be converted to a DCMG.
Next, based on eliminating these AC-DC converter components from ACMG, an efficient fully DCMG system is introduced that contains DC loads, such as electrolysers, and Photovoltaic (PV) and Battery Energy Storage (BES) systems.

The proposed investigations can significantly address the new technical demand for implementing DCMG-H2 using the low-cost energy from PVs and can enable up-scaling of hydrogen production.

An Extensive Comparison between MMC Topologies with different number of Sub-Modules

This digest describes a modular multi-level converter (MMC) scheme to connect renewables to the grid with minimal filter requirement. The PWM scheme generates a multi-level voltage output with low loss, low harmonic distortion, and design flexibility. It presents a comparison of the MMC topology with a different number of sub-modules. The last section focuses on the energy storage in capacitors with a different number of sub-modules under different conditions. The stored energy can be useful for fault ride through during grid fault conditions.

Inter-cluster Power Control of Modular Multilevel Converters with Integrated Battery Energy Storage for EV Low Voltage Operation

This paper presents a method to operate each MMC cluster with independent powers during low ac voltage operation. The method reduces the use of circulating current in low voltage conditions. This facilitatates the state of charge balance of MMCs with integrated BESS in the clusters for such conditions. The method is proposed for EVs but other applications could eventually make use of it.

Design and Implementation of 3.5 kW Digital Controlled Battery Charge System

A 3.5 kW digital controlled battery charger is implemented with the ripple feed forward (RFF) technique to reduce the output voltage ripple. This battery charger is composed of front-stage of interleaved boost converter for PFC and full-bridge resonant converter for DC-DC conversion. The full load conversion efficiency of the full-bridge resonant converter is 94.3%, and the highest efficiency of system is 93.9%. Mostly, the output voltage ripple is reduced about 30 % by using the RFF.

Control of Redundant Submodules in a Cascaded H-Bridge Converter-based Battery Energy Storage System

Cascaded H-bridge (CHB) converter is a suitable topology to integrate battery energy storage systems (BESSs) into the power system. Redundant submodules (SMs) are implemented in the CHB converter for higher reliability. However, in the literature, there is a dearth of dedicated research on the control of redundant SMs in this application. This paper proposes a control scheme for the redundant SMs in the CHB-based BESS. The proposed control scheme is able to safely activate and operate the redundant SMs that are not integrated with batteries. Simulation results are provided to verify the effectiveness of the proposed control scheme.

Hybrid Sorting Strategy for Modular Multilevel Converters With Partially Integrated Second Life Battery Energy Storage Systems for fast EV charging

Electric vehicles charging stations requires huge amounts of power from the grid, what can be alleviated with battery energy storage systems. Two-Level converter is the preferred topology for commercial BESS, but this topology do not offer modularity for the energy storage stage. This work proposes a parallelized Modular Multilevel Converter with partially rated storage systems with an overall control scheme that governs independently the active power reference of each BESS-SMs. The proposed control allows the operation with any amount of Dummy-SMs, which are SMs with floating capacitors in their DC-link without battery energy storage unit. This feature allows the converter to keep operating under batteries faults or disconnection, facilitating the integration of 2nd life batteries to BESS-SMs with different degradation levels. The intra-power balance and the control of the capacitors voltage of Dummy-SMs, is achieved through an hybrid sorting of carriers made in the modulation stage, where LS-PMW is used. This hybrid control strategy, allows the converter to operate each of its SMs as BESS or Dummy, depending of the connection or disconnection of its BESS.