Stoyan Bekiarov

Uninterruptible power supplies: classification, operation, dynamics, and control

This paper presents a comprehensive review of uninterruptible power supply (UPS) systems in terms of topologies, operation, dynamics and control. UPS systems are classified with emphasis on static systems. This paper also addresses fundamental problems faced in these systems in different distributed and centralized applications. In addition, a brief description of the conventional UPS systems, their disadvantages, scope for improvement, advanced architectures, role of power electronics and current trends in UPS research are explained. Negative impedance dynamics in UPS systems with constant power loads are also introduced. Finally, this paper concludes with a brief outline of the advancement to be made in the future.

An On-Line UPS System With Power Factor Correction and Electric Isolation Using BIFRED Converter

This paper presents the design consideration and performance analysis of an on-line, low-cost, high performance, and single-phase uninterruptible power supply (UPS) system based on a boost integrated flyback rectifier/energy storage dc/dc (BIFRED) converter. The system consists of an isolated ac/dc BIFRED converter, a bidirectional dc/dc converter, and a dc/ac inverter. It provides input power factor correction, electric isolation of the input from the output, low battery voltage, and control simplicity. Unlike conventional UPS topologies, the electrical isolation is provided using a high frequency transformer that results in a smaller size and lower cost. Detailed circuit operation, analysis, as well as simulation and experiment results are presented. A novel digital control technique is also presented for UPS inverter control. This controller follows the reference current and voltage of the inverter with a delay of two and four sampling periods, respectively.

A new reduced parts on-line single-phase UPS system

This paper presents design considerations and performance analysis of a new reduced parts on-line single-phase uninterruptible power supply (UPS) system. The proposed new UPS system is based on the half-bridge topology. It employs only five IGBTs and one diode reducing the cost of the system compared to the conventional on-line UPS topology, while achieving excellent performance. The common neutral eliminates the need for an isolation transformer and makes the system cheaper and more compact. The proposed UPS system uses a step down battery charger avoiding the problems associated with the high battery voltage, such as: space, cost, reliability, and safety issues. It has sinusoidal input current with unity power factor and high quality output voltage even with nonlinear loads. Detailed circuit operation and analysis as well as simulation and experimental results are presented.

A new on-line single-phase to three-phase UPS topology with reduced number of switches

This paper presents design considerations and performance analysis of a new on-line single-phase to three-phase uninterruptible power supply (UPS) system with reduced number of switches. The proposed new UPS system consists of an integrated rectifier/boost converter with power factor correction (PFC) capabilities and a two-leg inverter connected to a split DC-link bus. Two battery sets are directly connected to the DC-link bus resulting in a very simple system. The proposed topology uses only 6 active switches reducing the cost of the system compared to the traditional 7, 8, and 10-switch topologies. It has sinusoidal input current with unity power factor and high quality output voltages even with nonlinear loads. Detailed circuit operation and analysis as well as simulation and experimental results are presented.

An on-line UPS system with power factor correction and electric isolation using BIFRED converter

This paper presents design consideration and performance analysis of an on-line, low-cost, high performance single-phase Uninterruptible Power Supply (UPS) system based on Boost Integrated Flyback Rectifier/Energy storage DC/DC (BIFRED) converter. The system consists of an isolated AC/DC BIFRED converter, a bi-directional DC/DC converter, and a DC/AC inverter. It has input power factor correction, electric isolation of the input from the output, and control simplicity. Detailed circuit operation, analysis, as well as simulation and experiment results are presented.

Reduced parts three-phase series-parallel UPS system with active filter capabilities

In this paper, a new three-phase series-parallel line-interactive uninterruptible power supply (UPS) topology is presented. The new topology has less number of power electronic devices as well as control functions. Most of the power is supplied directly from the AC line to the load. Therefore, the overall efficiency is higher than that of on-line UPS. Different operating modes of the system and series and parallel converters are investigated as well. Simulation and experimental results are presented, which show the viability of the proposed topology.

Electricity restructuring in Bulgaria

This paper discusses the current situation for the restructuring of the electricity power sector in Bulgaria. It also outlines the major issues related to the restructuring in EU and Central and Eastern European (CEE) countries. The paper discusses the social and technical problems that the Bulgarian power industry are expected to face during the transition from monopoly to competitive markets. In addition, the paper provides a set of recommendations for the proposed restructuring measures in the Bulgarian power sector.

Design and Implementation of a Mobile Single-Phase AC Power Supply for Land Vehicles with 28V/200V Dual Voltage Alternators

In land vehicles with high-power electrical loads, other than the low-voltage DC bus (14V, 28V, or 42V) for the low-power conventional loads, a high-voltage bus, e.g., 200V DC, is required for high-power loads such as hotel loads and electrically-assisted propulsion systems. In addition, some advanced electrical loads including luxury loads and AC power point require 120V, 60Hz AC voltage. These land vehicles include heavy duty, fire fighting, and military vehicles. There are two traditional approaches in obtaining a dual DC voltage bus system. The first one is to obtain the low-voltage DC from the alternator and boost it to the high-voltage DC. The second method is to obtain the high-voltage DC directly from the alternator and reduce it to the low-voltage. Both approaches require additional step-up or step-down power conversion stages, which inherently result in a reduced efficiency. In this paper, a new approach with a 28V/200V dual voltage alternator is considered. This system avoids the additional power conversion stage and, as a result, increases the efficiency of the system. The primary objective of this paper is to demonstrate the design and operation of a high power density, 2.5 kW, single-phase, DC/AC pulse width modulated (PWM) inverter. The IGBT-based inverter operates from the 200V DC voltage output of the dual voltage alternator and consists of a low-pass LC filter at its output. The RMS value of the AC output voltage attained from the mobile power supply is 120V at a frequency of 60Hz. The sinusoidal pulse width modulation (SPWM) method is used as the control technique for the purpose of inverter switching. These PWM control signals are generated using a digital signal processor (DSP) and are eventually used to drive the gates of the IGBT switches of the proposed inverter. Due to the simplified power stage and the usage of an efficient DSP-based modulation technique, the total harmonic distortion (THD) of the output voltage is fairly low (less than 2%) and a relatively small overall inverter size is achieved. A detailed description of the system along with simulation and experimental results are presented in this paper.