Operation of Resonant DC/DC Converter in the BUCK Operation Regime

The series resonant DC/DC converter with isolation transformer is investigated. When switching frequency of input inverter bridge is above the resonant one a shortening of the naturally half-waves of current through a L-C resonant circuit takes place resulting in a circulating current through the DC supply source reducing a mean value of supply current and also reducing load voltage in respect to the one at normally resonant case. The main relations for the case with strong voltage supply source are obtained and operation regimes at raised switching frequency investigated using a computer modeling. Some conclusions are made for proper calculation of parameters. It is shown that the shape of the resonant circuit current at raised frequency grows to the triangular one and that asks for proper correction of the expressions obtained for sinusoidal case. Applying qZ input link processes quite differ from observed for the strong supply – arise charging of the capacitors of the link by influence of circulating current and this phenomena impedes to reducing of the load voltage. That qZ link does not allow to create proper regulation of load parameters.

Self-Excitation System for Synchronous Generator

Self-excitation for synchronous generator is described in the paper. The system is based on a buck converter input filter capacitor discharge through excitation winding of the generator. The buck converter is connected to the stator outputs through an uncontrollable diode rectifier, but excitation winding is used as a load. Input filter capacitor of the converter provides initial current pulse which magnetizes excitation system and produces the generator voltage increase, for this reason the capacitor is charged before self-excitation process starts. Results of the computer simulation and physical experiment are obtained and presented. These results show that the proposed self-excitation converter in conjunction with an input capacitor pre-charged from a low-power electronic generator actually magnetizes the generator excitation system therefore generator voltage and accordingly excitation current increases. Stabilization of generator output voltage occurs with a voltage surge, though its peak value slightly exceeds the reference one. The future investigation of the proposed self-excitation system may include definition of mathematical equations which describe transients in the generator’s self-excitation mode and development of control methods for purpose of self-excitation process control without voltage peaks. The computer model also should be improved

КВАЗИ-ИМПЕДАНСНЫЙ DC/DC ПРЕОБРАЗОВАТЕЛЬ С ПОСЛЕДОВАТЕЛЬНЫМ РЕЗОНАНСНЫМ LC-ЗВЕНОМ И МЯГКОЙ КОММУТАЦИЕЙ

This paper discusses further modifications of the recent popular qZS-based DC/DC converter design by the introduction of the resonant LC circuit in series to the primary winding of the isolation transformer. The primary aim is to achieve the zero voltage and zero current switching of transistors. As an additional benefit of the resonant LC circuit, the converter is able to perform the voltage buck function simply by changing the switching frequency of the transistors. The control principle of the converter and its main operating modes are explained. The theoretical assumptions are experimentally verified by help of the small-scale testbench of the converter.Предложена модификация схемы квази-импедансного DC/DC преобразователя путем последовательного включения резонансного LC-звена и первичной обмотки изолирующего трансформатора. Это позволяет достичь коммутации транзисторов при нулевом токе и нулевом напряжении. К дополнительным преимуществам предложенной схемы DC/DC преобразователя можно отнести способность понижать напряжение путем изменения частоты коммутации транзисторов. Рассмотрен принцип управления преобразователем и его основные режимы работы. Предложенные гипотезы были экспериментально подтверждены с помощью лабораторного макета.Предложена модификация схемы квази-импедансного DC/DC преобразователя путем последовательного включения резонансного LC-звена и первичной обмотки изолирующего трансформатора. Это позволяет достичь коммутации транзисторов при нулевом токе и нулевом напряжении. К дополнительным преимуществам предложенной схемы DC/DC преобразователя можно отнести способность понижать напряжение путем изменения частоты коммутации транзисторов. Рассмотрен принцип управления преобразователем и его основные режимы работы. Предложенные гипотезы были экспериментально подтверждены с помощью лабораторного макета