Multi-Level Voltage-Source Duty-cycle Modulation: Analysis and Implementation

Multi-level converters have become increasingly popular due to high power quality, high-voltage capability, low switching losses, and low EMC concerns. Considering these advantages, the multi-level converter is a suitable candidate for implementation of future naval ship propulsion systems. This paper focuses on modulation techniques for the multi-level converter. In particular, a novel voltage-source method of multi-level modulation is introduced and compared to existing methods. The proposed method is discrete in nature and can therefore be readily implemented on a digital signal processor (DSP). The method is also readily extendable to any number of voltage levels. Results of experimental implementation are demonstrated using a four-level rectifier/inverter system, which incorporates diode-clamped multi-level converters and an eleven-level cascaded multi-level H-bridge inverter

Reduced-Parts-count Multilevel Rectifiers

Multilevel power converters have gained much attention in recent years due to their high power quality, low switching losses, and high-voltage capability. These advantages make the multilevel converter a candidate topology for the next generation of naval ship prolusion systems. The primary disadvantage of these systems is the large number of semiconductors involved. This paper presents a reduced-parts-count rectifier which is well suited for naval rectifier applications where bidirectional power flow is not required. The proposed converter is analyzed and experimentally verified on an 18-kW four-level rectifier/inverter system

Analysis of a Four-level DC/DC Buck Converter

In this paper, a four-level DC/DC buck power converter is introduced. The primary application for this converter is to regulate the center capacitor voltage in a four-level inverter system. The steady-state and average-value models for the proposed converter are developed and compared in simulation. The converter was constructed in the laboratory and verified on a four-level motor drive system. It was shown that the four-level DC/DC converter provides capacitor voltage balancing and allows higher output voltage utilization from the inverter

Analysis of a Four-level DC/DC Buck Converter

In this paper, a four-level DC/DC buck converter is introduced. The primary application for this converter is to regulate the center capacitor voltage in a four-level inverter system. The steady-state and average-value models for the proposed converter are developed and compared in simulation. The converter was constructed in the laboratory and verified on a four-level motor drive system. It was shown that the four-level DC/DC converter provides capacitor voltage balancing and allows higher output voltage utilization from the inverter

Dynamic Average-Value Modeling of a Four-Level Drive System

Multilevel power converters have gained much attention in recent years due to their high power quality, low switching losses, and high-voltage capability. These advantages make the multilevel converter a candidate for the next generation of naval ship prolusion systems. Evaluation of these systems is typically assisted with a dynamic average-value models in order to rapidly predict system performance under several operating scenarios. In this paper, an average-value model is developed for the four-level diode-clamped converter which takes into account the active capacitor voltage balancing control. This model performance prediction is compared to a detailed model and laboratory measurements on an 18 kW rectifier/inverter test system

A Flux-weakening Strategy for Current-Regulated Surface-mounted Permanent-magnet Machine Drives

Permanent-magnet synchronous machines fed from current-regulated converters feature nearly ideal performance at low-to-moderate speeds. However, as rotor speed increases the back emf rises which results in loss of current regulation and decreased torque. In buried-magnet machine drives, flux weakening is often used to extend the speed range. This paper sets forth a flux-weakening control specifically designed for surface-mounted permanent-magnet machines which is simple and does not require knowledge of the machine or system parameters. The proposed method is demonstrated both experimentally and through the use of computer simulatio

Employees\u27 Perceived Effectiveness of Outsourcing Department of Defense Functions

The United States Department of Defense spends billions of dollars annually on outsourcing functions to private contracted companies without knowing if their actions are effective. Guided by Feigenbaum, Henig, and Hamnett\u27s theory of privatization and President Eisenhower\u27s warnings of the impending military-industrial complex, the intent of this grounded theory study was to develop relevant theory regarding how the Department of Defense might accomplish missions through outsourcing during current and future fiscal constraints. This study sought to understand the perceived effectiveness of outsourcing Department of Defense functions through the perspectives of 2 employment groups directly affected by such outsourcing: federal employees and privately contracted employees. In this study, 24 federal employees and 20 privately contracted employees completed qualitative surveys about their perceptions of effectiveness in regards to outsourcing Department of Defense functions. Data were inductively analyzed through open, axial, and selective coding via constant comparison. Findings from this study generated a grounded theory, one positing that 2 distinct elements are important in outsourcing during fiscal constraint: well defined legal requirements and private sector technical expertise. Evidence from this study suggests that when these elements are in place, outsourced Department of Defense functions can progress, regardless of fiscal restrictions. The implications for social change include assisting political leaders with better decision making in support of effective national security policies, while providing good stewardship of tax payer funds

Analysis of a Current-Regulated Brushless DC Drive

Current-regulated brushless DC machines are used in a wide variety of applications including robotics, actuators, electric vehicles, and ship propulsion systems. When conducting system analysis of this or any other type of drive, average-value reduced-order models are invaluable since they provide a means of rapidly predicting the electromechanical dynamics and are readily linearized for control system synthesis. In this paper, a highly accurate average-value reduced-order model of a hysteresis current-regulated brushless DC drive is set forth. In so doing it is demonstrated that the drive exhibits five distinct operating modes. The physical cause of each of these modes is explained and a mathematical model for each mode is set forth. The mathematical models are verified both experimentally and through the use of computer simulation. It has been found that the model set fourth herein is on the order of 300 times faster than a detailed computer simulation in calculating electromechanical transient

Control of Cascaded Multi-level Inverters

A new type of multi-level inverter is introduced which is created by cascading two three-phase three-level inverters using the load connection. This new inverter can operate as a nine-level inverter and naturally splits the power conversion into a higher voltage lower-frequency inverter and a lower-voltage higher frequency inverter. This type of system presents particular advantages to naval ship propulsion systems which rely on high power quality, survivable drives. New control methods are described involving both joint and separate control of the individual three-level inverters. Simulation results demonstrate the effectiveness of both controls. A laboratory set-up at the Naval Surface Warfare Center power electronics laboratory was used to validate the proposed joint-inverter control. Due to the effect of compounding levels in the cascaded inverter, a high number of levels are available resulting in a voltage THD of 9 % (without filtering)

Transient and Dynamic Average-Value Modeling of Synchronous Machine Fed Load-Commutated Converters

A new average-value model of a synchronous machine fed load-commutated converter is set forth in which the stator dynamics are combined with the DC link dynamics. This model is shown to he extremely accurate in predicting system transients and in predicting frequency-domain characteristics such as the impedance looking into the synchronous machine fed load-commutated converter. The model is verified against a detailed computer simulation and against a hardware test system, thus providing a three-way comparison. The proposed model is shown to be much more accurate than models in which the stator dynamics are neglecte