Herbert L. Hess

Modeling and analysis of a flywheel energy storage system for Voltage sag correction

The U.S. Navy is looking for methods to maximize the survivability of combat ships during battle conditions. A shipboard power distribution system is a stiff isolated power system that is vulnerable to voltage sags, which arise due to faults or pulsed loads, which can cause interruptions of critical loads. A series voltage injection type flywheel energy storage system (FESS) is used to mitigate voltage sags and maximize the survivability of the ship. The basic circuit consists of an energy storage system, power electronic interface, and a series injection transformer. In this case, the energy storage system consists of a flywheel coupled to an induction machine. The stored energy is used for sag correction for the critical load. Indirect field-oriented control (IDFOC) with space-vector pulsewidth modulation (SVPWM) is used to control the induction machine. Sinusoidal PWM is used for controlling the power system side converter. This paper presents the modeling, simulation, and analysis of a FESS with a power converter interface using PSCAD/EMTDC.

Transformerless capacitive coupling of gate signals for series operation of power MOS devices

A reliable configuration for triggering a series string of power metal oxide semiconductor (MOS) devices without the use of transformer coupling is presented. A capacitor is inserted between the gate and ground of each metal oxide semiconductor field effect transistor (MOSFET), except for the bottom MOSFET in the stack. Using a single input voltage signal to trigger the bottom MOSFET, a voltage division across the network of device capacitance and inserted capacitances triggers the entire series stack reliably. Design formulas are presented and simple circuit protection is discussed. Simulation shows reliable operation and experimental verification is presented, Application of the method is applied to series insulated gate bipolar transistors (IGBTs).

Modeling and analysis of a flywheel energy storage system for voltage sag correction

The US Navy is looking for methods to maximize the survivability of combat ships during battle conditions. A shipboard power distribution system is a stiff, isolated power system that is vulnerable to system transients. Power quality problems, such as voltage sags, which arise due to a fault or a pulsed load, can cause interruptions of critical loads. Critical loads include radar systems, pumps and weapon systems. A series voltage injection type flywheel energy storage system is proposed to mitigate voltage sap and maximize the survivability of the ship. The bask circuit consists of an energy storage system, power electronic interface and a series injection transformer. In this case the energy storage system consists of a flywheel coupled to an induction machine. The flywheel stores energy In the form of kinetic energy and the induction machine is used for energy conversion. The power electronic interface facilitates the bi-directional flow of power for charging and discharging the flywheel through the induction machine. The stored energy is used for sag correction when the critical load sees a voltage sag. Indirect field oriented control with space vector PWM is used to control the induction machine. Sinusoidal PWM is used for controlling the power system side converter. This paper presents the modeling, simulation and analysis of a flywheel energy storage system with a power converter interface using PSCAD/EMTDC.

A Scalable High-Voltage Output Driver for Low-Voltage CMOS Technologies

A monolithic implementation of series connected MOSFETs for high-voltage switching applications is presented. Using a single low-voltage control signal to trigger the bottom MOSFET in the series stack, a voltage division across parasitic and inserted capacitances in the circuit is used to turn on the entire stack of devices. This voltage division both statically and dynamically safeguards the individual MOSFETs over the entire switching period. Because the output voltage is balanced across each device in the stack for the entire switching period, stress to the oxide and hot-carrier degradation are minimized, even in the event of transient over voltages. This circuit, termed the Stacked MOSFET, is ntimes scalable, allowing for the on-die control of voltages that are ntimes the fabrication processes rated operating voltage. The governing equations for this circuit are derived and reliable operation is demonstrated through simulation and experimental implementation in a 0.35-mum SOI CMOS process. The realized prototype is shown to handle 2times the nominal process operating voltage at a switching frequency of 20 MHz with an input-to-output delay of only 5.5 ns

The modeling and simulation of a permanent magnet synchronous motor with direct torque control based on Matlab/Simulink

This paper introduces the modeling of the direct torque control (DTC) system of permanent magnet synchronous motor based on Matlab/Simulink. The process of the building simulation system is discussed in detail. Simulation results are presented to help understand the system performance and the influence of PI controller parameters on it. The relationship between torque hysteresis loops width and torque ripple amplitude is analyzed and the result shows that the torque ripple can be reduced by narrowing the torque hysteresis loops width. The simulation also demonstrates the PI controller parameters Kp and Ki should be properly matched to achieve high system performance. The simulation results and user-friendly graphic user interface proved that Matlab /Simulink is an effective tool to simulate and analyse a motor drive system

Modulation Strategies for a New SCR-Based Induction Motor Drive System with a Wide Speed Range

A new SCR-based naturally commutated induction motor drive that provides high torque over a wide speed range is presented. Topology is similar to that of certain naturally commutated current source inverters, but modulation techniques and system performance are very different. Two novel switching algorithms are proposed to cover the low-speed and high-speed regimes. Torque ripple is negligible in the low-speed region. With these two switching techniques, commutation is reliable and operation within peak device voltage stress limits is guaranteed. For induction machine loads, this drive has the torque-speed capability typical of a cycloconverter (but with far fewer devices), plus a field weakening range that the cycloconverter does not have. Simulation and experimental results are presented

A literature review of state of-charge estimation techniques applicable to lithium poly-carbon monoflouride (LI/CFx) battery

Almost as long as rechargeable batteries have existed, systems able to give an indication about the state-of-charge (SoC) of a battery have been around. Several methods, including those of direct measurements, bookkeeping and adaptive systems are known in the art for determining the SoC of a cell or battery of cells. An accurate SoC determination method and an understandable and reliable SoC display to the user will improve the performance and reliability, and will ultimately lengthen the lifetime of the battery. However, many examples of poor accuracy and reliability can be found in practice. This review presents an overview on battery technology and the state-of-the-art of SoC methods. The goal of all the presented SoC indication methods is to design an SoC indication system capable of providing an accurate SoC indication under all realistic user conditions, including those of spread-in both battery and user behaviour, a large temperature and current range and ageing of the battery.

Zero sequence method for energy recovery from a variable-speed wind turbine generator

An innovative power conversion system to convert energy from a variable-frequency wind-powered induction generator to a fixed frequency output is presented. A standard six-switch DC link current regulated pulse width modulated (CRPWM) inverter is simultaneously modulated with two current components. A three-phase balanced current component at the induction generators optimum operating frequency transfers energy from the generator to the converter. A single phase zero sequence current component at a fixed 60 Hz frequency transfers energy from the converter through a zero sequence filter to the load. Unity power factor output is shown both in simulation and experiment, though any arbitrary power factor output may be readily commanded. Maximum power capture for a variable-speed wind turbine is achieved using proven control techniques. This method uses only half of the active power switching devices of conventional conversion methods. Simulation and experimental verification are shown.

Fuel cell propulsion system for marine applications

A fuel cell propulsion system for a small ship is recommended. The paper reviews the ships current power system and its limitations. The paper describes why fuel cells are a better option for ship propulsion and describes how fuel cells could be integrated into the ship. A discussion of different high power fuel cell modules and power conditioning systems for fuel cells is also presented.

Intelligent neural network implementation for SOCI development of Li/CFx batteries

The State Of Charge Indicator (SOCI) for the Lithium Poly Carbon Monoflouride (Li/CFx) battery has a wide range of applications. However, the dynamic environmental conditions, such as the ambient temperature, can alter the characteristic response of the battery and introduce non-linear behavior. This paper discusses the in-lab development of an Artificial Neural Network (ANN) based SOCI for the Li/CFx battery. The ANN is trained on the recorded data - voltage, current and ambient temperature, to produce a non-linear model and to accurately predict the State Of Charge (SOC) of the battery. The SOC prediction is based on the recent behavior of the battery. Preliminary experimental results using recorded datasets from the Battery Design Studio are presented for the Lithium Ion battery. The working model for the Li/CFx is currently under development. The reported results demonstrated good performance of the developed SOCI, with less than 2% average relative error on data at previously observed ambient temperatures.