O. Garcia

Automotive DC-DC bidirectional converter made with many interleaved buck stages

Interleaving technique is used in some applications due to its advantages regarding filter reduction, dynamic response, and power management. In dual battery system vehicles, the bidirectional dc-dc converter takes advantage of this technique using three-to-five paralleled buck stages. In this paper, we propose the use of a much higher number of phases in parallel together with digital control. It will be shown that this approach opens new possibilities since changes in the technology are possible. Thus, two 1000-W prototypes have been designed using surface mount technology devices (SO-8 transistors). An additional important feature is that due to the accuracy of the digital device [field-programmable gate array (FPGA)], current loops have been eliminated, greatly simplifying the implementation of the control stage

FPGA-Based Digital Pulsewidth Modulator With Time Resolution Under 2 ns

This paper proposes a new digital pulsewidth modulation (DPWM) architecture that takes advantage of the field-programmable gate arrays (FPGA) advanced characteristics, especially the delay-locked loop (DLLs) present in almost every FPGA. The proposed DPWM combines a synchronous (counter-based) block with an asynchronous block for increased resolution without unnecessarily increasing the clock frequency. The experimental results show an implementation in a low-cost FPGA (Xilinx Spartan-3) that uses an external 32 MHz clock for a final time resolution under 2 ns.

Digital-Control-Based Solution to the Effect of Nonidealities of the Inductors in Multiphase Converters

Multiphase is an old technique that, nowadays, is widely used in several dc-dc applications such as voltage regulator module and automotive. The number of phases is usually kept relatively low (three or four) in most cases. However, the advantages of multiphase converters (mainly the reduction of input and output filters with its associated increase in maximum control bandwidth) grow with the number of phases in the ideal case. This growth is limited by nonidealities, mainly the tolerances of components (semiconductors and inductors). The purpose of this paper is to evaluate the effect of tolerances of the inductance on the current ripple. This nonideality causes the loss of two important advantages of multiphase converters, such as very high frequency and very low amplitude current ripple. The use of digital control can help to reduce drastically this problem. A simple algorithm, based on changing the triggering sequence of the phases, allows a big reduction of the impact of this nonideality. Experiments are included in the paper.

Current Self-Balance Mechanism in Multiphase Buck Converter

Some of the recent applications in the field of the power supplies use multiphase converters to achieve fast dynamic response, smaller input/output filters, or better packaging. Typically, these converters have several paralleled power stages, with a current loop in each phase and a single voltage loop. The presence of the current loops avoids current imbalance among phases. The purpose of this paper is to demonstrate that, in CCM, with a proper design, there is an intrinsic mechanism of self-balance that reduces the current imbalance. Thus, in the buck converter, if natural zero-voltage switching (ZVS) is achieved in both transitions, the instantaneous inductor current compensates partially the different DC currents through the phases. The need for using n current loops will be finally determined by the application but not by the converter itself. Using the buck converter as a base, a multiphase converter has been developed. Several tests have been carried out in the laboratory and the results show clearly that, when the conditions are met, the phase currents are very well balanced even during transient conditions.

Tight magnetic coupling in multiphase interleaved converters based on simple transformers

Magnetic integration and magnetic coupling are very promising concepts to be applied in multiphase converters. Tight magnetic coupling allows energy transfer among phases. Ideally the magnetic component can act as a voltage source, with very low output impedance and with a perfect sharing of output current ripple. The main advantages provided by magnetic coupling are size and losses reduction and dynamic improvement. In this paper two winding transformer arrangements to be used in multiphase converters are presented, and validated with a new integrated transformer.

Bi-directional DC/DC Converter for Hybrid Vehicles

Hybrid vehicles need a high voltage DC bus to supply power to the motor. Architectures of these vehicles usually include a DC-DC bi-directional converter between this voltage bus and the conventional battery. When the DC bus is held by a big capacitor, the selection and design of the aforementioned converter has an additional difficulty since the converter has to work with an output voltage ranging from 0 to 420 V in steady-state conditions. A bi-directional DC-DC converter for a hybrid vehicle is proposed in this paper. It can be used in the case that a big capacitor holds the voltage in the high side. The application forces three different operation modes being the converter able to operate in those conditions. Experimental results of a 1500 W prototype are included in the paper

EMI reduction by interleaving of power converters

Switched converters are a source of EMI due to the hard switching and abrupt edges in the current and voltage waveforms. Interleaved converters can reduce the EMI at the source, minimizing the generation of conducted EMI, without changing the normal operation of the circuit. Input filter can be reduced, radiated EMI is lower and internal EMI problems are minimized. This paper is focused on exploring the capabilities of the interleaved converters to reduce conducted EMI, taking into account the non-idealities of the actual converters.

Comparison of current doubler rectifier and center tapped rectifier for low voltage applications

It is well known that the current doubler rectifier is very suitable for low voltage (1V-2V) and very high current (50A-100A) dc-dc converters. However, at lower current applications (30A, 20A, 10A), it is not clear which is the more appropriate rectifier the current doubler or the center tapped. The goal of this paper is to identify the application area of these rectifiers. The output current together the output current ripple/output current ratio (/spl Delta/I/I/sub O/) are important parameters to select the more suitable rectifier.

Coreless Magnetic Transformer Design Procedure

The calculation of resistance and inductance of magnetic components without a core is not a simple task. Since the magnetic field distribution is 2D/3D, the models that have to be applied should consider such field distribution. The use of analytical expressions may help to obtain a rough approximation of the inductance value. However, an accurate calculation of coupling and resistance requires a more accurate approach like FEA solvers. This paper describes a full procedure to design coreless magnetic components. The proposed procedure is based on the use of analytical expressions in order to select the appropriate number of turns and winding positioning, and the use of FEA solvers in order to calculate the whole component model, including AC resistance and coupling

Current self-balance mechanism in multiphase back converter

Some of the recent applications in the field of the power supplies use multiphase converters to achieve fast dynamic response, smaller input/output filters or better packaging. Typically, these converters have several paralleled power stages with a current loop in each phase and an unique voltage loop. The presence of the current loops is necessary to increase dynamic response (by using current mode control) and to avoid current unbalance among phases. The purpose of this paper is to demonstrate that in CCM, with a proper design, there is an intrinsic mechanism of self-balance that helps a lot in avoiding the current unbalance. Thus, in the buck converter, if natural ZVS is achieved in both transitions, the instantaneous inductor current compensates partially the different dc current through the phases. The need for using n current-loops will be finally determined by the application but not by the converter itself. Using the buck converter as a base, a multiphase converter has been developed. Several tests have been carried out in the lab and the results show clearly that, when the conditions are met, the phase currents are very good balanced even during transient conditions.