Mustafa Farhadi

Energy Storage Technologies for High-Power Applications

Energy storage systems provide viable solutions for improving efficiency and power quality as well as reliability issues in dc/ac power systems including power grid with considerable penetrations of renewable energy. The storage systems are also essential for aircraft powertrains, shipboard power systems, electric vehicles, and hybrid electric vehicles to meet the peak load economically and improve the systems reliability and efficiency. Significant development and research efforts have recently been made in high-power storage technologies such as supercapacitors, superconducting magnetic energy storage (SMES), and flywheels. These devices have a very high-power density and fast response time and are suitable for applications with rapid charge and discharge requirements. In this paper, the latest technological developments of these devices as well as advancements in the lithium-ion battery, the most power dense commercially available battery, are presented. Also, a comparative analysis of these high-power storage technologies in terms of power, energy, cost, life, and performance is carried out. This paper also presents the applications, advantages, and limitations of these technologies in a power grid and transportation system as well as critical and pulse loads.

Adaptive Energy Management in Redundant Hybrid DC Microgrid for Pulse Load Mitigation

This paper investigates the real-time control and energy management of a dc microgrid incorporating hybrid energy sources with various loading schemes. In the proposed dc microgrid, a supercapacitor bank, a power buffer, and a pulse load are directly connected to a dc bus. The proposed system configuration highly improves the grid redundancy and reduces the total power losses. Moreover, the supercapacitor bank not only supplies the pulse load, but also supports the grid during transient periods when it is highly loaded. However, the energy management and control of such a system is more complex, since the heavy pulse load can cause high power pulsation and voltage drop. To reduce the adverse effects of the pulse load, a new real-time energy management system (EMS) with an adaptive energy calculator (AEC) based on the moving average measurement technique is developed. The proposed microgrid was implemented in hardware and experimentally tested. The results were compared with other methods, such as direct voltage control and continuous current averaging approaches. The results show that the developed EMS with AEC technique properly share the power and control the bus voltage under different loading conditions, while the adverse effects of the pulse load are highly reduced.

Real-Time Operation and Harmonic Analysis of Isolated and Non-Isolated Hybrid DC Microgrid

In this paper, the real-time operation and the harmonic analysis of isolated and nonisolated dc microgrid are investigated. The microgrid features hybrid energy sources with various loading schemes. This hybrid dc microgrid was supplied by an internal generator and the ac utility grid. A supercapacitor bank functions by acting as a power buffer to satisfy the high power requirements of the dc microgrid. In order to properly manage the energy and prevent the ac grid power pulsation, a current-voltage control technique based on master-slave control concept is proposed. In this technique, the supercapacitor bank operates as the master and controls the dc bus voltage. The other converters are working in current control mode to share the required power. The controllers of the converters are equipped with hysteresis voltage control, which monitors the entire supercapacitor bank. Additionally, an analog hysteresis voltage protection circuit board was designed and implemented to protect the supercapacitor cells from overvoltages that can occur due to uneven charge distribution during the fast charging processes. The protection circuit, which was developed and built here, was experimentally tested, and its error was analyzed. Various operating modes based on different power sharing patterns were defined. The experimental test was carried out for both galvanically isolated and nonisolated dc grid systems. The results show that the proposed energy management algorithm properly shares power and control the voltage. In addition, depending on the power sharing pattern, the isolation of the dc microgrid significantly affects the harmonic content of the current.

Realtime operation and harmonic analysis of isolated and non-isolated hybrid DC microgrid

In this paper, the real-time operation and the harmonic analysis of isolated and nonisolated dc microgrid are investigated. The microgrid features hybrid energy sources with various loading schemes. This hybrid dc microgrid was supplied by an internal generator and the ac utility grid. A supercapacitor bank functions by acting as a power buffer to satisfy the high power requirements of the dc microgrid. In order to properly manage the energy and prevent the ac grid power pulsation, a current-voltage control technique based on master-slave control concept is proposed. In this technique, the supercapacitor bank operates as the master and controls the dc bus voltage. The other converters are working in current control mode to share the required power. The controllers of the converters are equipped with hysteresis voltage control, which monitors the entire supercapacitor bank. Additionally, an analog hysteresis voltage protection circuit board was designed and implemented to protect the supercapacitor cells from overvoltages that can occur due to uneven charge distribution during the fast charging processes. The protection circuit, which was developed and built here, was experimentally tested, and its error was analyzed. Various operating modes based on different power sharing patterns were defined. The experimental test was carried out for both galvanically isolated and nonisolated dc grid systems. The results show that the proposed energy management algorithm properly shares power and control the voltage. In addition, depending on the power sharing pattern, the isolation of the dc microgrid significantly affects the harmonic content of the current.

Event-Based Protection Scheme for a Multiterminal Hybrid DC Power System

In this paper, we investigate an event-based protection scheme for a multiterminal dc power system, which includes hybrid energy resources and various loading schemes. The proposed protection scheme transfers less data when compared with commonly used data-based protection methods, and does not require high-speed communication and synchronization. Each protection unit is able to autonomously identify the type of event using the current derivative fault identification method, employing an artificial inductive line impedance. In order to accurately set the protection relays, detailed fault current analysis considering low pass resistor capacitor filter effects are presented. The decision for fault isolation is made based on the unit judgment and the data received through high-level data communication from other interconnected units. The performance of the proposed protection scheme was evaluated under different dc feeder and bus faults. The results show that this scheme is able to accurately identify the type of fault, isolate the faulted area, and restore the system quickly while limiting the load voltage drop to its preset limit.

Performance Enhancement of Actively Controlled Hybrid DC Microgrid Incorporating Pulsed Load

In this paper, a new energy control scheme is proposed for actively controlled hybrid dc microgrid to reduce the adverse impact of pulsed power loads. The proposed energy control is an adaptive current-voltage control (ACVC) scheme based on the moving average measurement technique and an adaptive proportional compensator. Unlike conventional energy control methods, the proposed ACVC approach has the advantage of controlling both the voltage and current of the system while keeping the output current of the power converter at a relatively constant value. For this study, a laboratory-scale hybrid dc microgrid is developed to evaluate the performance of the ACVC strategy and to compare its performance with other conventional energy control methods. Using experimental test results, it is shown that the proposed strategy highly improves the dynamic performance of the hybrid dc microgrid. Although the ACVC technique causes slightly more bus voltage variation, it effectively eliminates the high current and power pulsation of the power converters. The experimental test results for different pulse duty ratios demonstrated a significant improvement achieved by the developed ACVC scheme in enhancing the system efficiency, reducing the ac grid voltage drop and the frequency fluctuations.

Operation and protection of photovoltaic systems in hybrid AC/DC smart grids

In this paper, some of the aspects related to the design, control, operation and protection of photovoltaic (PV) systems are presented and investigated. The photovoltaic systems under study are integrating their power to the common DC bus of a hybrid AC/DC microgird in a smart grid infrastructure, where a communication layer is allowing wide area monitoring, control and protection of the whole system. These PV systems can be mainly operated either in a voltage control mode, when the DC side of the system is disconnected from the main AC grid, or in a maximum power point tracking (MPPT) mode when connected to the DC bus. The control of the power conditioning units interfacing the PV panels to the rest of the systems in these two modes of operation is investigated. Furthermore, the protection of these converters against different types of faults will be also investigated. Simulation and experimental results are included in the paper to justify the validity of the ideas and concepts discussed.

A New Protection Scheme for Multi-Bus DC Power Systems Using an Event Classification Approach

DC microgrid systems with hybrid energy resources are of significant interest in shipboard and spacecraft applications. In such a system, coordinated operation of circuit breakers (CBs) and disconnecting switches (DSs) can rapidly isolate short circuit faults and restore the system very fast. In this paper, we investigate a new protection scheme for a multi-bus DC systems based on an event classification approach. The proposed protection scheme transfers less data when compared with commonly used data-based protection methods and does not require high speed communication and synchronization. The results show that the developed protection scheme is able to identify the type of fault accurately, isolate the faulted area and restore the system very quickly while maintaining continuous power to the loads.

Performance enhancement of actively controlled hybrid DC microgrid with pulsed load

In this paper, a new energy control scheme is proposed for actively controlled hybrid dc microgrid to reduce the adverse impact of pulsed power loads. The proposed energy control is an adaptive current-voltage control (ACVC) scheme based on the moving average measurement technique and an adaptive proportional compensator. Unlike conventional energy control methods, the proposed ACVC approach has the advantages of controlling both voltage and current of the system while it keep the output current of the power converter at a relatively constant value. For this study, a laboratory scale hybrid dc microgrid is developed to evaluate the performance of the ACVC strategy and to compare its performance with the other conventional energy control methods. Using experimental test results, it is shown that the proposed strategy highly improves the dynamic performance of the hybrid dc microgrid. Although the ACVC technique causes slightly more bus voltage variation, it effectively eliminates the high current and power pulsation of the power converters. The experimental test results for different pulse duty ratios demonstrated a significant improvement achieved by the developed ACVC scheme in enhancing the system efficiency, reducing the ac grid voltage drop and the frequency fluctuations.

Comparative analysis of energy control techniques for DC microgrid and pulsed power load applications

DC Microgrid power systems are becoming increasingly common in many applications. In this work, the comparative analysis of different energy control techniques for a dc microgrid with pulsed power loads is considered. A laboratory scale hybrid dc microgrid is developed to evaluate the performance of the energy control methods. In the proposed dc microgrid, a supercapacitor bank, acting as power buffer, and a pulse load are directly connected to a common coupling dc bus while the injected power to the grid is regulated through power converters. This microgrid is connected to an AC grid test-bed to further analyze the consequence of the pulse loads. The test results show that the energy control methods are different in terms of their maximum power requirement, their performance on the dc microgrid, and their effects on the ac grid.