Luiz D. S. Bezerra

A Nonisolated DC-DC Boost Converter With High Voltage Gain and Balanced Output Voltage

This paper presents a dc-dc boost converter with high voltage gain based on the three-state switching cell for split-capacitor neutral-point-clamped inverters. The proposed converter is analyzed considering the operation in continuous conduction mode and duty cycle higher than 0.5, which corresponds to overlapping mode. The main characteristics of the topology are operation at high switching frequency, whereas the input inductor is designed for twice such frequency; in order to minimize weight and volume, the voltage stress across the switches is lower than half of the output voltage and naturally clamped by one output capacitor, allowing the use of MOSFET transistors with reduced intrinsic on-resistance; the input current presents small ripple; the output voltage can be further stepped up by increasing the transformer turns ratio without compromising the voltage stress across the switches; and the output voltage is naturally balanced, thus making the converter suitable for supplying split-capacitor inverters. Several topologies where a high voltage step-up is possible are initially investigated in the literature. Then, the principle of operation and experimental results for a 1-kW prototype are presented to validate the theoretical analysis and demonstrate the converter 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 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.

DC-DC nonisolated boost converter with high voltage gain adequate for split-capacitor inverter applications

This paper presents a dc-dc boost converter with high voltage gain based on three-state switching cell for split-capacitor neutral-point clamped inverters. The proposed converter is analyzed considering the operation in continuous conduction mode and duty cycle higher than 0.5, which corresponds to overlapping mode. The main characteristics of the topology are: operation at high switching frequency, while the input inductor is designed for twice such frequency; in order to minimize weight and volume, the voltage stress across the switches is lower than half of the output voltage and naturally clamped by one output capacitor, allowing the use of transistors MOSFETs with reduced intrinsic on-resistance; the input current presents small ripple; the output voltage can be further step up by increasing the transformer turns ratio without compromising the voltage stress across the switches; the output voltage is balanced thus making the converter suitable for supplying split-capacitor inverters. Several topologies where high voltage step up is possible are initially investigated in literature. Then the principle of operation, the design methodology, and experimental results for a 1kW prototype are presented to validate the theoretical analysis and demonstrate the converter performance.

Electronic circuit for stand-alone wind energy conversion system

This paper presents an electronic circuit for stand-alone systems application. The converters architecture is composed by a battery charge controller, a step-up converter based on three-state switching cell, and a voltage source inverter (VSI). All of them operate with pulse width modulation (PWM) technique. The battery charge controller is a classic boost converter that operates in continuous conduction mode (CCM) and it is used to regulate the battery bank voltage, and also to reach the maximum power point from wind turbine. The second converter is a step-up, where a secondary winding is coupled to the transformer to raise the battery voltage up to 400VDC. It also operates in CCM applying two overlapping gate signals. In order to perform the DC-AC conversion, a classical voltage source inverter operating with unipolar voltage switching technique is used. Principles of operation, as well as, experimental results of the assembled prototype are presented.

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.

A new step-up high voltage gain dc-dc converter

A new high voltage gain dc-dc converter is proposed on this work as a viable solution to step-up a low battery voltage into a high voltage dc link. This converter is suitable for non-isolated on-line UPS systems with common neutral connection, that improves bypass circuit installation. Furthermore, smaller size, higher efficiency, and increased reliability are features that spread the transformerless products. The adopted control strategy uses a hybrid control that implements both analog and digital controllers, that implements the average current mode control. It presents characteristic of continuous input current through the batteries that improve its lifetime, the maximum voltage across the controlled switches is equal to one fourth 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.

Three-phase UPS with high power factor and high frequency transformer isolation

This work proposes an double conversion three-phase uninterruptible power system (UPS) with power factor correction, high frequency (HF) transformer isolation, and suitable for operation with line-to-line input voltages equal to 220 V or 380 V. For both input voltages, the proposed converter has almost the same efficiency processing the same output power. The structure is composed by single-phase chopper modules, single-phase boost modules, and one three-phase inverter . The relevant features are soft commutation of the controlled switches in the chopper stage, simple control strategy that can be implemented with well-known integrated circuits (IC), and the use of few batteries in series due to the same reference of the step-up stages. Principle of operation of the proposed system, implemented control strategy and experimental results obtained for a 15 kVA prototype are presented.

Comparison of VRLA-AGM batteries lifetime charging with different currents waveforms for use on low power UPS

This paper aims to present a study of storage capacities of absorbed glass mat (AGM) valve regulated lead acid (VRLA) batteries with pulsating and non-pulsating currents charging methods. In the testing process, three batteries were charged with pulsating current, and one battery is charged with continuous current free of AC ripple. When the battery is charged with pulsed current, the RMS current is higher and it is related to the increase of internal power losses, I2R, which cause a temperature rise, and as consequence there is loss of water from the electrolyte. To show this, the charging pulse current waveforms were modeled, and both currents compared. To make the experimental tests, the UPS chargers were connected to the batteries during 24 hours, then they are removed and placed at rest mode during 3 hours, and later discharged draining a constant current of 7.2A (1C) using electronic load until reaching the minimum voltage of 9.6V. The charge and discharge tests were made up to achieve 80% of the nominal battery storage capacity from IEEE Std 1188-2014 standard recommendation for VRLA batteries replacement [1]. The capacity measurements of the battery, as a function of the number of deep discharge cycles are shown to verify the lifetime of the batteries.

Control strategy for multifunctional, three-phase, four wire, AC-DC boost converter

This paper presents control strategy for multifunctional, three-phase, four wire AC-DC converters. The converter is named multifunctional because it operates as a battery charger and as a load power supply. In other words, two different loads in parallel are connected simultaneously to the converter. For this purpose same current and voltage signals are necessary to send to the control circuit. The indicated signals are, input main currents, output load currents, battery bank currents, voltage across of each battery bank, total output voltage, and input main voltages for feed-forward networks and current shape. The proposed converter control strategy is applied in non-isolated three-phase UPS systems. The relevant features of the proposed converter control strategy are, power factor correction, common neutral point between input and output to facilitate bypass circuit installation, symmetrical divided output voltage for inverters with neutral point, and battery current control with high power factor. Principle of operation of the control circuit and experimental results obtained from a small power scale prototype are presented.