Babak Parkhideh

Design and development of Generation-I silicon based Solid State Transformer

The Solid State Transformer (SST) is one of the key elements proposed in the National Science Foundation (NSF) Generation-III Engineering Research Center (ERC) “Future Renewable Electric Energy Delivery and Management” (FREEDM) Systems Center. The SST is used to enable active management of distributed renewable energy resources, energy storage devices and loads. In this paper, the Generation-I SST single-phase 20kVA, based on 6.5kV Si-IGBT is proposed for interface with 12kV distribution system voltage. The SST system design parameters, overall system efficiency, high frequency transformer design, dual active bridge converter, auxiliary power supply and gate drives are investigated. Design considerations and experimental results of the prototype SST are reported.

Reconfigurable Solar Converter: A Single-Stage Power Conversion PV-Battery System

This paper introduces a new converter called reconfigurable solar converter (RSC) for photovoltaic (PV)-battery application, particularly utility-scale PV-battery application. The main concept of the new converter is to use a single-stage three-phase grid-tie solar PV converter to perform dc/ac and dc/dc operations. This converter solution is appealing for PV-battery application, because it minimizes the number of conversion stages, thereby improving efficiency and reducing cost, weight, and volume. In this paper, a combination of analysis and experimental tests is used to demonstrate the attractive performance characteristics of the proposed RSC.

Improving distribution system performance with integrated STATCOM and supercapacitor energy storage system

The STATCOM (synchronous static compensator) based on voltage source converter (VSC) is used for voltage regulation in transmission and distribution systems. However, strict requirements of STATCOM losses and total system loss penalty preclude the use of high frequency PWM (pulse-width modulation) for VSC based STATCOM applications. This constraint of implementing VSC without PWM results in VSC DC voltage dip, over-currents and trips of the STATCOM during and after system disturbances and faults, when its VAR support functionality is most required. In this paper, the integration and control of energy storage systems (ESSs), such as supercapacitor (ultracapacitor - UCAP) into a D-STATCOM (Distribution system STATCOM) is developed to mitigate such problems, enhance power quality and improve distribution system reliability. This paper develops the control concepts to charge/discharge the UCAP by the D-STATCOM, and validate the performance of an integrated D-STATCOM/UCAP system for improving distribution system performance under all types of system related disturbances and system faults - such as single-line to ground fault (SLG), line-line fault and 3-phase system faults. Simulation results of a 125 kVA D-STATCOM validate that integrated the D-STATCOM with 600 V, 1.0 Farad UCAP is suited for distribution system voltage regulation and voltage sag mitigation. In case of a system fault, UCAP based energy storage will aid to keep the D-STATCOM DC voltage constant and avoid over-current and trips of the VSC based D-STATCOM.

Vector-Controlled Voltage-Source-Converter-Based Transmission Under Grid Disturbances

Voltage-source converter (VSC)-based transmission systems have attractive potential features in terms of power flow control and stability of the network. Although relatively low switching frequency operation of high-power converters (9-15 times the line frequency) is desirable, it makes them sensitive to power network imbalances when they may be needed the most. This paper specifically proposes a control structure to improve the performance of high-power vector-controlled back-to-back VSC systems for conventional and emerging utility applications. The main improvement is to suppress the possible dc-link voltage fluctuations under power line faults and unbalanced conditions. The proposed controller structure is designed based on regulating the converter systems states locally in dq synchronous reference frame without sequence components extraction or resonant notch compensator. RTDS results verify the validity of the proposed control architecture during normal and unbalanced power system conditions.

Design and implementation of distributed control architecture of an AC-stacked PV inverter

A control scheme for a distributed Inverter Molecule™ architecture is analyzed and implemented in this paper. An Inverter Molecule is a building block for a novel distributed inverter architecture suitable for PV/Battery applications which exceeds the performance metrics obtained by Central/String- inverters with or without DC/DC optimizers or by Micro-Inverters. The proposed transformerless architecture utilizes low-voltage semiconductor devices with much higher yields than their high-voltage counterparts. A group of Inverter Molecules operate autonomously and cooperatively to maintain the grid interconnection requirements while providing maximum power control on each molecules PV panel. This paper overviews the state-of the-art control methods implemented mostly on cascaded H-bridge derived topologies and further establishes a distributed control scheme for Inverter Molecule architecture that does not need any high bandwidth communications except a heartbeat signal at line frequency. Experimental results are presented for a lab-scaled prototype.

Strategies for competing energy storage technologies for in DC fast charging stations

The universal acceptance of electric vehicles depends on the widespread presence of charging stations. These stations have to be designed intelligently so as not to overwhelm the fragile power grid with the additional load. In this paper we extend our previous work in [1] and examine how the charging station performance, namely the blocking probability, is affected both by the energy storage technology used, and the employed charging strategy. We consider two strategies: charging from the energy storage first, and charging from the power grid first. We compare their performance for different sets of system parameters and identify the optimum operating rule. Finally, we describe an economic model, which allows us to determine the trade-offs involved when choosing between an energy storage with higher capacity or one with a higher power rating.

Improved wind farm’s power availability by battery energy storage systems: modeling and control

This paper presents the study on the integration of battery energy storage system (BESS) to STATCOM for smoothing out the intermittent output power of a wind farm. Lead-acid battery type is considered as the energy storage system for availability and comparably simpler management system. Reviewed several modeling approaches indicating their advantages and drawbacks; particularly, appropriate for high power applicationspsila time-frames, current-based third order model is developed. The experimental tests are conducted to identify the parameters and consequently, to construct the battery model. The performance of the proposed system is analyzed by introducing the state-of-charge (SOC) controller implemented for this type of battery integrated to a proposed 10 MVA STATCOM for a 50 MW wind farm.

Development of current measurement techniques for high frequency power converters

Current sensing plays dominant role in power converters, where current information can be used for controlling, monitoring and protection. One of the most challenging goals in modern power electronics converters is to increase switching frequency for the purpose of miniaturization, and improve the performance especially for end-users. Therefore, the need for accurate, lossless, and fast response current sensors is more highlighted. This paper presents a comprehensive review of different current sensing schemes for power electronics applications. The Challenges for implementation of conventional methods for high frequency (>1MHz) and high current converters will be addressed. More specifically, technical issue and hardware difficulties for developing Rogowski-based as well as Hall effect current sensors are discussed and finally, a new technique for improving the performance of Anisotropic Magneto-Resistive (AMR) at 1MHz and 30V with a new technique is shown.

Real-time Hardware-in-the-Loop simulation of convertible static transmission controller for transmission grid management

We propose a Convertible Static Transmission Controller (CSTC) concept that enables coordinated power flow control with emphasis on large penetration of renewable energy resources based transmission in a meshed network. CSTS can be connected across the substation power transformer and reconfigured for different modes of operation to perform as a versatile transmission controller with several functions including: power flow control for transmission of renewable resources, and as a transformer back-up for disaster management and/or life extension purposes. Different connecting configuration options, i.e. shunt-shunt, series-shunt, and series-series can be obtained. In this paper, we demonstrated the viability of the proposed concept using Typhoon HIL400 ultra-high fidelity Hardware-in-the-Loop (HIL) system in three different modes of operation. HIL simulations are used to verify the validity of the proposed control architecture for CSTC operation during both normal and unbalanced power system conditions for different connecting configurations.

Convertible Static Compensator (CSC) performance under system fault

Convertible Static Compensator (CSC) which is a versatile FACTS technology has been installed on Marcy 345 kV substation and increases power transfer capability, operational functionality, and power flow controllability of the New York Power Authority (NYPA) transmission system. This paper presents a detailed description of CSC inverter operation and PSCAD simulation results of the CSC when it is operating as a STATCOM. The STATCOM steady state and dynamic operation simulation results under different conditions including unbalanced condition and faults is discussed. For fault condition analysis, attention is focused to Double L-G (LLG) fault at three different locations, one very close and two others electrically far from STATCOM terminals. This paper also demonstrates the effectiveness of the emergency PWM (EPWM) strategy a solution for limiting the poles current and preventing STATCOM over current tripping during fault conditions.