A. Shenkman

Novel AC-DC and DC-DC converters with a diode-capacitor multiplier

This paper presents a transformerless ac-dc and or dc-dc converter with a high output voltage multiplicity, which contains only one switch. The converter consists of an inverter and a diode-capacitor multiplier (DCM) and provides a voltage gain equal to double the number of multiplier steps. In the case of ac-dc conversion the proposed converter offers a practically unit power factor and provides a sine wave input current. The analysis of the steady state as well as the transient behavior of the DCM is given and simplified equivalent circuits are proposed. The prototype of the DCM has been built and tested to show the validity of the proposed converter. The theoretical analysis, the computer simulation results, and the experimental testing results are in good agreement.

A new simplified model of the dynamics of the current-fed parallel resonant inverter

In this paper, the transient analysis of a current-fed parallel inverter, widely used in industrial applications (such as for the heating and melting of metals), is performed. A high-inductance smoothing inductor is usually connected in the input of the inverter and its load may be represented by a parallel resonant circuit characterized by high quality factor Q. To simplify the dynamic analysis of such an inverter, approximating it by a second-order switchless continuous dynamic link (i.e., RLC circuit) is suggested. The comparative analysis of the inverter and approximating circuit, whose parameters are properly chosen, shows the permissibility of such an approximation. It also shows how to assure desired aperiodic dynamic behavior. Then, by analyzing the approximating circuit, the expressions for inverter parameters are found. With these expressions, the values of a smoothing inductor, a compensating capacitance and a voltage factor, in order to ensure the aperiodic behavior of the inverter, can be calculated. The results of the proposed analysis were checked on laboratory and industrial prototypes of the above inverter. The theoretical and experimental results are in good agreement.

A novel diode-capacitor voltage multiplier for increasing the voltage of photovoltaic cells

A new scheme of a diode-capacitor network, used as a DC voltage multiplier is proposed. The circuit operates in combination with a high-frequency switch. In contrast to the present similar circuits, during the operational process the capacitors are not shortened by the switch and therefore the large discharge current stresses donpsilat influence the circuit. The circuit provides the multiplication of the input voltage having a smooth (very small ripples) input current and output voltage. The advantages of the proposed circuit make it very appropriate for use with alternative sources of energy. SPICE-simulation and the experimental results confirm the theoretical expectations.

An approximate analysis of a starting process of a current source parallel inverter with a high-Q induction heating load

An approximate analysis of the start-up process of a resonant loaded current source parallel inverter is presented. The proposed approach may be applied to inverters whose industrial applications are induction heating and metal melting installations. To estimate the eigenvalues of the third-order set of differential equations, the iteration method has been used. By using the arrived at formulas it is possible to select inverter thyristors that meet the inverter start-up characteristics. The approximate formulas accuracy was estimated by computer-aided analysis. It is shown that at the inverter starting process the turn-off angle changing may be of two kinds: monotonous or oscillating. Regions of inverter parameters that cause one or the other of these two processes are determined. When the changing of the turn-off angle is monotonous, the achieved approximate formulas can be used. The analysis of the oscillating process was performed by applying the experimental design theory statistical methods to the computer-simulation results and the approximate formulas for the oscillating region were also obtained. Two examples of the inverter design procedure and thyristor choosing techniques are given. Finally, an experimental verification of the calculation results is performed.

Assuring continuous input current using a smoothing reactor in a thyristor frequency converter for induction metal melting and heating applications

The approximate analysis of a thyristor frequency converter for induction heating and melting is described. The method for calculating the smoothing reactor inductance, which will provide the continuous mode of inverter input current operation, is proposed. The laboratory prototype of the above converter has been made and examined. The results of the experiments are in good agreement with the theoretical calculations.

Algebraic Representation of DC-DC Converters and Symbolic Method of their Analysis

The algebraic representation of idealized DC-DC PWM converters covering various structures and their connection is given. The algebra is constructed on the basis of hyper-complex numbers - hypernions and allows the analysis of the structures of the converters by using of a symbolical method. The possibility of the calculation of a discontinuous current and soft switching is also considered. Such an abstract description of various schemas allows reducing their variety to several basic structures and formalizes a problem of the synthesis of the converters with the desired parameters. The numerical solution of the algebraic expressions is easily carried out with the help of the standard mathematical programs MATHCAD or MATLAB.