Dan Lascu

A new quadratic buck converter

A new type of quadratic buck converter is presented, analyzed, simulated and experimented in the continuous conduction mode (CCM), the usual way that converters are used. Because of the static conversion ratio dependency on the duty cycle the new converter is ideal for applications where only a small voltage step-down is needed. The converter consists of one transistor, three diodes, two inductors and two capacitors.

Stability and bifurcation aspects in charge controlled DC-DC converters

Continuous conduction mode operated dc-dc converters employing the charge control technique is investigated regarding stability, bifurcation and chaotic aspects. The proposed mathematical approach is general twofold: the analysis is converter independent and it and can be applied to any other control strategies provided the converter is CCM operated. Starting from an exact state-space description of the converter the exact duty cycle and the exact reference voltage value at the border of the stability region are calculated. The approach used also allows to predict the nature of the bifurcation. The theoretical concepts developed in the paper are accurately verified twice: first by discrete state-space simulation in Matlab and then by circuit simulation under the Caspoc package.

A new general mathematical technique for stability and bifurcation analysis of DC-DC converters applied to one-cycle controlled buck converters with non-ideal reset

This paper brings two major contributions: the first investigates and draws conclusions about stability and bifurcation phenomena related to one-cycle controlled dc-dc converters when non-ideal reset is encountered. The second introduces a new general mathematical technique for deriving stability and bifurcation behavior in continuous conduction mode operated dc-dc converters. Up to now, one-cycle control analysis assumed the integrator is instantly reset and in these conditions it was demonstrated that one-cycle control is always stable. In the present work it is proven that even with an ideal converter, when the integration capacitor is discharged over a nonzero resistor the system becomes unstable at high duty cycles. The stability condition with respect to the control voltage is analytically derived using a new general proposed technique. This approach can be applied to any control such as: traditional current mode control, predictive current control, charge control, one cycle control or feedback loops employing different regulators. Moreover, it can be used with different types of modulation: leading-edge, trailing-edge or double-edge modulation. When applied to one-cycle controlled buck converters employing a non-ideal resettable integrator, it is proven that bifurcation phenomena are encountered. This behavior with period doubling instability is confirmed by Matlab and Caspoc simulations.

Predictive leading-edge modulation average current control in DC-DC converters

The paper investigates predictive digital average current control (PDACC) in dc/dc converters using leading-edge modulation (LEM). The study is focused on the recurrence duty cycle equation and then, based on it, stability analysis is performed. It is demonstrated that average current control using leading-edge modulation is stable on the whole range of the duty cycle and thus design problems are highly simplified. The analysis is carried out in a general manner, independent of converter topology and therefore the results can be easily applied for a certain converter topology (buck, boost, buck-boost, etc.). The theoretical considerations are verified using both MATLAB and finally with the CASPOC circuit simulation package. Some simulation aspects regarding the new developed dedicated blocks are also presented.

Analysis of one cycle controlled SEPIC converters

This paper demonstrates that one cycle control (OCC) technique cannot be used in conjunction with continuous conduction mode (CCM) operated Sepic converters, as it inherently leads to unstable operation. The approach adopted by the authors to prove this is similar to that used to investigate current-mode controlled converters, except for the fact that the perturbation is referred to the capacitive voltage applied across the diode when off. It is demonstrated that in CCM this perturbation is amplified from one switching cycle to another and thus it results in instability. The theoretical results are verified through computer simulation using the Caspoc package.

A novel stacked step-down switching converter

A new step-down dc-dc converter with one active switch and two diodes is presented. DC analysis is performed and static characteristics are derived, and then device stresses are evaluated and compared to other buck topologies. Design equations are provided, a prototype is simulated and finally experimentally tested. The measurements proved the feasibility of the proposed circuit. This novel converter could be a solution for applications where a small difference between the input and output voltages is needed.

A new stacked step-up converter

A new step-up converter with one active switch and two diodes is proposed. Static properties are derived after a dc analysis and then components stresses and ripples are evaluated and design procedures are provided. The theoretical concepts are confirmed by simulation. Finally, a prototype is built and the experimental results confirmed the feasibility of the new topology. The new proposed converter exhibits higher step up conversion compared to the classical boost. Moreover, in the same application, semiconductor voltage stresses are lower for the new converter compared to the classical one, while semiconductor current stresses are the same.

A new hybrid Boost-L converter

The paper proposes a new step-up topology with high step-up conversion ratio. Dc analysis is performed and the static characteristics are derived revealing that the static conversion ratio exhibits a high voltage boost, the converter still operating at reasonable duty cycles. Compared to a classical Boost, the static conversion ratio at the same duty cycle D is (1+nD) time higher, where n is the transformer ratio. Compared to quadratic converters the proposed topology exhibits also one transistor and three diodes, but it contains only one capacitor and only one magnetic device resulting that two reactive elements are eliminated. Design equations are provided and the converter is simulated and experimental tested. The simulation accurately confirmed the theoretical behavior and the experiments where in perfectly agreement with the simulation and theory. This novel converter could be a simple cheap solution in applications where an output voltage much higher than the input voltage is needed.

Stability analysis of DC-DC converters employing digital predictive leading triangle modulation valley current control

Stability of predictive digital valley current control (PDVCC) in dc/dc converters using leading triangle modulation (LTM) is investigated. The study is focused on the recurrence duty cycle equation and then stability analysis is performed. It is demonstrated that PDVCC using LTM is unstable on the whole range of the duty cycle. The analysis is carried out in a general manner, independent of converter topology and therefore the results can then be easily applied for a certain converter topology (buck, boost, buck-boost, etc.). The theoretical considerations are confirmed for a boost converter first using the MATLAB program based on state-space equations and finally with the CASPOC circuit simulation package.

A novel low-stress high-efficiency step-up DC-DC converter

The paper introduces a novel boost topology exhibiting comparable efficiency but lower semiconductor voltage stresses compared to the classical boost converter. Operation of the converter in continuous conduction mode (CCM) is similar to that of the classical hard-switched PWM converter, except for the fact that a resonant interval is introduced in the first topological state. After all design equations are derived, the theoretical aspects are verified against the simulations and finally the experiments accurately confirmed the feasibility of the new proposed architecture.