СТІЙКІСТЬ КОМБІНОВАНОЇ СИСТЕМИ НАКОПИЧЕННЯ ЕНЕРГІЇ НА ОСНОВІ СУПЕРКОНДЕНСАТОРА ТА АКУМУЛЯТОРНОЇ БАТАРЕЇ

The aim of the work is to analyze the stability of the battery-supercapacitor hybrid storage of power supply for resistance micro-welding equipment, considering the possible variation of the system parameters and taking into account parallel series resistance of the circuit components. Methodology. The sufficient accurate mathematical model of the hybrid energy storage system to stability analysis has been obtained by the state-space average method. According to the state-space averaging method, PWM switching converters are described by separate circuit topologies for each switching period. The system of differential equations for each time interval has been derived by use of the Kirchhoff rules. The small-signal model transfer function of the SEPIC converter has been obtained by applying the Laplace transform to linear state equations averaged over one switching cycle. Finally, the Nyquist stability criterion has been considered to evaluate the stability of the proposed energy storage system. Results. Bode diagrams of an open-loop system for different values of the duty cycle, average load current, and input voltage have been obtained by using MATLAB software. The gain margin ranges from 14.6 dB to 26.4 dB and the phase margin ranges from 45.4 degrees to 54.8 degrees. From these results, it is obvious that the proposed system meets the stability criteria regardless of the aforementioned parameter fluctuations. Originality. The high-efficiency energy storage system for micro resistance welding technology has been proposed. Developing of the energy storage system according to the battery semi-active hybrid topology enables to control the Li-ion battery discharge current within the maximum allowable value. SEPIC converter utilization ensures the high-efficient operation of the power supply despite the battery charge state. Moreover, this topology allows implementing series and parallel configuration of both batteries and supercapacitors to obtain the required value of voltage and current. Practical significance. The mathematical model of the SEPIC converter has been developed by applying the state-space averaging technique. The stability analysis for parameter variation, such as duty cycle and the average load current, the input voltage has been performed by using Nyquist criteria. В роботі розглянуто комбінований ємнісний накопичувач енергії на основі акумуляторної батареї (АБ) та суперконденсатора джерела живлення для установки контактного мікрозварювання. Для забезпечення рівномірного споживання струму від АБ обрано напівактивну топологію АБ та перетворювач SEPIC (Single-Ended Primary-Inductor Converter). Методом усереднення в просторі змінних стану аналітично отримано математичну модель системи. З метою проведення аналізу стійкості комбінованого накопичувача при різних значеннях коефіцієнта заповнення імпульсів, струму навантаження та напруги АБ отримано передавальну характеристику системи керування. Результати аналізу показали, що запропонована система є стійкою при зміні параметрів у встановлених межах.

Charging Device of Capacitive Energy Storage for Micro Resistance Welding

Micro resistance welding is the most common technology for making permanent connection between two conducting materials. This paper proposes a high-efficiency charging device for the capacitive energy storage within the micro resistance welding device power supply utilizing a Flyback converter. Based on the comprehensive analysis of charging device losses, it is determined that one of the main sources of conduction losses in the charging device is the output diode. In order to ameliorate this problem, utilization of a MOSFET transistor as an output diode within the Flyback converter is proposed in order to increase its overall efficiency. The presented results suggest that the proposed Flyback converter topology could improve the power efficiency by 7.0% at 50 kHz switching frequency through minimization of conduction losses in comparison with the traditionally-used Schottky diode