Carlos G. C. Branco

A High Step-Up DC-DC Converter Based on Three-State Switching Cell

A new non-isolated boost converter with high voltage gain is proposed on this work. This converter is suitable for applications with a high voltage gain between the input and the output. In this converter, for a given duty cycle, the output to input voltage ratio can be raised by adding transformer turns. Another important feature of this converter is the lower blocking voltage across the controlled switches compared to similar circuits, which allows the utilization of MOSFETs switches with lower conduction resistances RDS(on). In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a 1 kW assembled prototype

A UPS With 110-V/220-V Input Voltage and High-Frequency Transformer Isolation

This paper proposes an isolated double-conversion uninterruptible power system with power factor correction using a high-frequency transformer and with input voltages equal to 110 V/220 V. The arrangement is suitable to rack-type structures because it has a small size and a reduced weight. For both input voltages, the proposed converter has almost the same efficiency processing the same output power. Other relevant features include soft commutation of the controlled switches in the chopper and boost stages, a simple control strategy that can be implemented with well-known integrated circuits, and the use of few batteries in series due to the step-up stage. Qualitative analysis and experimental results obtained with a 2-kVA prototype show a normal efficiency of over 86% for the worst case of input voltage and an input power factor of over 99%.

A Generalized High Voltage Gain Boost Converter Based on Three-State Switching Cell

A new non-isolated step-up converter with high voltage gain is proposed on this work. It is suitable for applications with a high voltage gain between the input and the output. In this converter, the output to input voltage ratio, for a given duty cycle, can be raised adding transformer turns ratio. Another important feature of this converter is the lower blocking voltage across the controlled switches compared to similar circuits, which allows the utilization of switches with low on-resistance RDS(on) MOSFETs. In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a 1 kW laboratory prototype

A Nonisolated Single-Phase UPS Topology With 110-V/220-V Input–Output Voltage Ratings

A circuit configuration of a single-phase nonisolated online uninterruptible power supply (UPS) with 110-V/220-V input–output voltage ratings is proposed, allowing the bypass operation without a transformer even if the input voltage is different from the output voltage. The converter consists of an ac–dc/dc–dc three-level boost converter combined with a double half-bridge inverter. In this type of configuration size, cost and efficiency are improved due to the reduced number of switches and batteries, and also, no low-frequency isolation transformer is required to realize bypass operation because of the common neutral connection. Both stages of the proposed circuit operate at high frequency by using a passive nondissipative snubber circuit in the boost converter and insulated-gate bipolar-transistor switches in the double half-bridge inverter, with low conduction losses, low tail current, and low switching losses. Principle of operation and experimental results for a 2.6-kVA prototype are presented to demonstrate the UPS performance.

High frequency isolation on-line UPS system for low power applications

In this paper, a new high frequency isolation on-line uninterruptible power supply (UPS) system is proposed as a viable solution for low power applications. Its composed by one half-bridge chopper that operates in open loop with fixed duty cycle, a step-up converter that operates in closed loop using the traditional average current mode control and a traditional full bridge voltage source inverter (VSI). The step-up converter control provides power factor correction to the system. The proposed circuit is suitable for the development of low power UPSs (less than 1 kVA) which few batteries are used. In such applications the battery bank voltage, can be 24 V, 36 V or 48 V. Principle of operation, as well as, experimental results for the UPS operating in both, grid and battery modes are presented. Accordingly to the experimental results for a 1 kVA assembled prototype, an efficiency of 81,3% is obtained for grid mode and 89,2% for the battery mode, confirming the effectiveness of the proposed configuration.

A new isolated DC-DC boost converter using three-state switching cell

In this paper, a new isolated DC-DC boost converter based on three-state switching cell (3SSC) is proposed. The mentioned cell allows the use of only two windings in the isolation transformer, as well as, the series connection of only one DC current blocking capacitor to avoid its saturation. Other relevant characteristics of the converter are, the blocking voltage across the controlled switches is low, which allows the utilization of lower drain-to-source conduction resistances (RDSon) MOSFETs, and the current through the autotransformer winding is almost continuous minimizing the hysteresis losses on the magnetic core. In this way, the efficiency of the proposed converter is high, and it is recommended for the development of power supplies using low voltage sources commonly found on renewable energy conversion systems and batteries. The converter was analyzed in overlapping of the control signals or duty cycle higher than 0.5 operating in continuous conduction mode (CCM). In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a lkW assembled prototype.

A low cost flyback-based high power factor battery charger for UPS applications

This paper proposes a feasible low cost isolated battery charger converter, which is powered directly by the ac mains voltage, and with characteristics of high power factor for uninterruptible power systems (UPS) applications. The main advantage of this converter is due to the fact of its total independence of the UPS online power stage. Thus, if the batteries capacity of the system are changed (i.e., the output power of the battery charger), no such modification are required to the main power stage of the UPS, such as re-design of the input ac/dc power stage for an higher or lower output power capacity. This re-design commonly occurs in UPS topologies that the battery charger is directly fed by the dc-link bus voltage, such as common neutral connections UPS. Another advantage is that the energy supplied to charge the batteries is processed by only one power processing stage, increasing the system reliability. As disadvantage of such converter is the reasonable efficiency. Experimental results and relevant curves regarding the proposed converter operation are shown, confirming the viability of such circuit.

A PFC pre-regulator with 110 V/220 V input voltage and high frequency isolation for UPS applications

This work deals with the development of a PFC pre-regulator circuit with possibility of 110 V/220 V AC main input voltages, while maintaining the same efficiency for a wide load range. Other relevant features of this circuit topology are high frequency transformer isolation, soft commutation of the controlled switches, simple control strategy that can be implemented with well-known integrated circuits and the use of few batteries in series due to step-up stage. This circuit is recommended for on-line UPS applications and it is convenient for the development in rack-type structures due to small size and reduced weight. Qualitative analysis and experimental results obtained from 1.6 kW prototype are presented

A Non-Isolated Single Phase On-Line UPS with Universal Input Output Voltage

This work deals with the development of a single phase on-line uninterruptible power supply(UPS) with universal input output voltage rating(110V/220V). The converter is consisted of an ac-dc/dc-dc three level boost converter combined with a double half bridge inverter. In this type of configuration, size, cost and efficiency are improved due to the fact of reduced number of switches, batteries and not requiring isolation transformer operating in lower frequency to realize bypass operation. A higher frequency operation of both converters is adopted using a passive non-dissipative snubber circuit in the boost converter and latest available commercial technology of IGBTs switches in inverters. A simple and well known control strategy is presented. Principle of operation, simulated results and experimental results of a 2.6kVA prototype is also presented to demonstrate UPS performance.

A step-Up DC-DC converter for non-isolated on-line UPS applications

A new non-isolated boost converter with high voltage gain is proposed in this work. This converter is suitable for nonisolated on-line UPS systems, with common neutral connection, that improves bypass circuit installation. The adopted control strategy uses a hybrid control that implements both analog and digital controllers, that implements the average current mode control. It presents characteristics of continuous input current through the batteries that improve its lifetime, the maximum voltage across the controlled switches is equal to half of the total output voltage, and voltage equalization across the dc-link capacitors is intrinsic. In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a 1.55 kW assembled prototype.