Ujjal Manandhar

Hybrid Optimization for Economic Deployment of ESS in PV-Integrated EV Charging Stations

Electric vehicle (EV) charging stations will play an important role in the smart city. Uncoordinated and statistical EV charging loads would further stress the distribution system. Photovoltaic (PV) systems, which can reduce this stress, also show variation due to weather conditions. In this paper, a hybrid optimization algorithm for energy storage management is proposed, which shifts its mode of operation between the deterministic and rule-based approaches depending on the electricity price band allocation. The cost degradation model of the energy storage system (ESS) along with the levelized cost of PV power is used in the case of EV charging stations. The algorithm comprises of three parts: categorization of real-time electricity price in different price bands, real-time calculation of PV power from solar irradiation data, and optimization for minimizing the operating cost of EV charging station integrated with PV and ESS. An extensive simulation study is carried out with an uncoordinated and statistical EV charging model in the context of Singapore to check effectiveness of this algorithm. Furthermore, detailed analysis of subsidy and incentive to be given by the government agencies for higher penetration of renewable energy is also presented. This work would aid in planning of adoption of PV-integrated EV charging stations, which would expectedly replace traditional gas stations in future.

Optimization of Charge/Discharge Rates of a Battery Using a Two-Stage Rate-Limit Control

Summary form only given. The complete presentation was not made available for publication as part of the conference proceedings. Energy storage would play a critical role in the microgrids. In this paper, two stage variable rate-limit control for battery energy storage is proposed. The objective of this control scheme is to optimize the amount, rate and time-duration of the energy stored/discharged from the battery. Thus, the battery would charge/discharge at its optimized maximum rate in a hybrid energy storage system (HESS). Supercapacitor is used to form the hybrid energy storage system, to complement or supply the energy deficiency during the transient period. With the proposed control scheme, the stress levels on the battery is regulated by optimizing the charge/discharge rates of the battery. The advantages of the proposed control scheme also includes maintaining the state of charge (SOC) of the battery within the limits for longer duration. This control scheme is validated using real-time control hardware in loop (CHIL) using OPAL-RT and dSPACE.

Validation of Faster Joint Control Strategy for Battery- and Supercapacitor-Based Energy Storage System

Energy storage system (ESS) is generally used to manage the intermittency of the renewable energy sources (RESs). The proper control strategy is needed to effectively maintain the power balance between the RESs, load demand, and ESS. The conventional control strategy for the hybrid energy storage system (HESS) uses the high-/low-pass filter method for system net power decomposition and the ESS power dispatch. In this paper, a new joint control strategy is proposed for photovoltaic-based dc grid system, with battery and supercapacitor (SC) as a HESS. The new joint control strategy utilizes the uncompensated power from the battery system to increase the performance of the overall HESS. The advantages of the proposed control strategy over the conventional control strategy are faster dc-link voltage restoration and effective power sharing between the battery and the SC. The detailed stability analysis of the proposed control strategy is also presented. The effectiveness of the proposed control strategy over the conventional control strategy is validated with the short-term and long-term experimental studies.

Energy storage management for EV charging stations: Comparison between uncoordinated and statistical charging loads

Electricity price is essential factor in the deployment of electric vehicles (EVs) on large scale. In wholesale electricity market, EV charging stations(ECS) connected with suitably sized energy storage system (ESS) can save substantial amount of money by managing their time of utilisation (TOU). In this study, a real-time EV charging model at ECS along with ESS degradation model is considered to analyse effect of the ESS for TOU pricing benefits. The objective is to minimize the EVs charging cost. The proposed algorithm focuses on real-time energy management using combination of heuristic approach and deterministic approach. The algorithm analyses electricity pricing trend using historical and forecasted statistical data and controls the power imported from the grid, while feeding dynamic EV charging load. Significant amount of cost saving is seen in results due to deployment of ESS in utilizing TOU pricing benefits of wholesale electricity price.

Application of two stage rate limit control for different operating modes of battery

The present work deals with the application of two stage rate limit control for battery energy storage system under different operating modes. Energy storage systems are playing very important role in renewable power systems and microgrids. Depending on the nature of power requirement, utilization of multiple energy storage units with distinguised characteristics in terms of power and energy density is quite common in microgrids. Batteries are one of the most commonly used energy storage systems in microgrids, to support slow transients or steady state load demands. The power charge/discharge rates affects the stress levels in the battery, which in turn affects the battery life span; and its power pattern affects stored/discharge energy from the battery, which in turn affects the state of charge (SOC) of the battery. Therefore, to optimize the charge/discharge rates a two stage rate limit control scheme is proposed, and its application for different operating modes is discussed in this paper. This control scheme is verified in OPAL-RT by creating real-time control hardware in loop (CHIL) with dSPACE.

Energy Management and Control for Grid Connected Hybrid Energy Storage System under Different Operating Modes

DC-coupled microgrids are simple as they do not require any synchronization when integrating different distributed energy generations. However, the control and energy management strategy between the renewable energy sources and the energy storages under different operating modes is a challenging task. In this paper, a new energy management scheme is proposed for the grid connected hybrid energy storage with the battery and the supercapacitor under different operating modes. The main advantages of the proposed energy management scheme are effective power sharing between the different energy storage systems, faster dc link voltage regulation to generation and load disturbances, dynamic power sharing between the battery and the grid based on the battery state of charge, reduced rate of charge/discharge of battery current during steady state and transient power fluctuations, improved power quality features in ac grid and seamless mode transitions. The effectiveness of the proposed method is validated by both simulation and experimental studies.

Enumerated-MPC-based dynamic voltage restorer using lc filter with damping resistor

This paper presents an enumerated model predictive control (MPC) based method for the dynamic voltage restorer (DVR), which consists of a series-connected transformer and a voltage source inverter. The filter adopted in the DVR is a LC filter with a damping resistor. The design of the discrete model for the voltage source inverter and the corresponding controller are discussed in this paper. The proposed method is capable to regulate the DVR to compensate the sag, swell and harmonic distortions of the grid voltage. Simulation studies are conducted to verify the performance of the proposed enumerated MPC-based method, and the simulation results demonstrate that the proposed method is effective to achieve the protection of the loads from the grid voltage sag, swell and harmonic distortion.

A stand-alone hybrid pv/fuel cell power system using single-inductor dual-input single-output boost converter with model predictive control

This paper presents a stand-alone hybrid PV/fuel cell system using single-inductor dual-input single-output (SI-DISO) boost converter. Compared to conventional hybrid power system, the proposed system significantly reduce the number of components, the system size and the corresponding cost. A model predictive control (MPC) method has been developed to control the SI-DISO boost converter to achieve the input power regulation and output voltage regulation. In order to verify the performance of the proposed hybrid PV/fuel cell power system based on SI-DISO boost converter and the corresponding MPC method, several simulation studies are conducted in Matlab/Simulink. The simulation results demonstrate that the proposed hybrid power system works effectively.

A DC microgrid integrated dynamic voltage restorer with model predictive control

This paper presents a DC microgrid integrated dynamic voltage restorer (DVR) system to mitigate the grid voltage sag and swell. The DC source of the DVR is the DC microgrid, including the PV array and hybrid energy storage system consisting of lithium-ion battery and supercapacitor. Compared to the conventional DVR supplied by pure energy storages, the DC microgrid will prolong the operation the DVR because the renewable energy source can supply the DVR or charge the HESS occasionally. The DVR is regulated by a model predictive control (MPC) method to conduct the compensation of voltage sag and swell. The design of the MPC method for DVR and controller for the system are presented in detail in this paper. In order to validate the performance of the DC microgrid integrated DVR system and the corresponding control method, several simulation studies are conducted including the scenarios of voltage sag and voltage swell. The simulation results indicate that the proposed system works effectively and achieve compensation of the grid voltage sag and swell successfully.