Pablo Antoszczuk

Current Control for High-Dynamic High-Power Multiphase Buck Converters

When it comes to high-power current sources, multiphase buck converters become an attractive alternative to deliver high currents. However, large variations in current reference or load voltage lead to disturbances that require high dynamics in the transitory response of current control. This letter presents a current control for high-dynamic, high-power multiphase buck converters. The control proposed is based on the synchronization of zero-crossing current ripples with a time reference pattern. This control forces a correct interleaving and is capable of responding, with a reduced transitory time, to major changes in current reference and load voltage. Experimental results validate the proposal.

Characterization of Steady-State Current Ripple in Interleaved Power Converters Under Inductance Mismatches

Interleaved power converters are used in high-current applications due to their inherent reduction of semiconductors stress and total ripple. Ripple reduction is accomplished by a correct phase shifting, and the filtering improvement explained by the increase in the ripple frequency. However, these benefits are wasted, among other reasons, by the mismatch of the phase inductor value. As a consequence, differences in the ripple amplitude among phases are produced, leading to a total current ripple significantly greater than the ideal case, the loss of the cancellation points and the generation of the switching frequency component and its harmonics. The works dealing with this subject matter have focused on particular cases, such as a given number of phases, a specific converter topology, or a particular case of inductance mismatch, disregarding a general analytical approach. This paper proposes an analytical method to characterize the total ripple in steady state as a function of the duty cycle and the number of phases under any condition on inductance mismatch. Experimental results validate the proposed method.

Optimized Implementation of a Current Control Algorithm for Multiphase Interleaved Power Converters

Multiphase converters have become an attractive alternative for high-current power converters due to their inherent reduction of semiconductor stress. Additionally, total current ripple frequency can be increased and its amplitude decreased by the phases ripple interleaving. These converters require a different number of phases and control specifications depending on the application. A wide range of applications imposes challenging requirements in the control algorithm and its implementation, such as digital platforms and resources optimization. A previous proposal presented a current control algorithm developed to provide a solution to the highly demanding constraints present in high-power applications, where short settling times are required when fast transients in the current reference or the load voltage are present. This work presents the implementation of the above-mentioned algorithm and its optimizations, aimed to obtain a modular and efficient design. The proposed implementation and system scalability are evaluated by means of an experimental setup.

Interleaved Current Control for Multiphase Converters With High Dynamics Mean Current Tracking

This paper presents a current control for high-power multiphase converters, where fast and precise current reference tracking is required, and limited switching frequency is present. The proposed control is based on a synchronization signal and current error comparison bands per phase. The control calculates the switching time that adjusts the phase current error zero-crossing points with the synchronization signal to control the current mean value and provide the correct phase shift among phases. The aforementioned comparison bands allow us to determine the current error slopes required to calculate the switching instants. This methodology permits the precise current reference tracking regardless the load voltage and the voltage drop in the semiconductor devices and in the series resistance of the phase inductors. Additionally, band-crossing information allows the fast detection of major changes in the current error, and the optimal system behavior decision, minimizing the transient time. Furthermore, the current control is stable in the complete duty cycle range, which is evaluated by means of a small-signal model. Experimental tests on a low-scale four-phase buck converter validate the proposal.

Interleaved Boundary Conduction Mode Versus Continous Conduction Mode Magnetic Volume Comparison in Power Converters

Power converters operating in boundary conduction mode (BCM) can benefit from an efficiency increase compared to continuous conduction mode (CCM) based on the soft-switching transitions at turn-on and/or turn-off. However, for a given average inductor current, the RMS current in BCM converters becomes larger than in CCM converters, leading to an increase in conduction losses. Interleaving smaller BCM power converters overcome this drawback by reducing the total ripple current amplitude at the expense of an increase in complexity and in magnetic parts count. Nevertheless, as the magnetic devices are among the largest components in power converters, it is convenient to find the design conditions under which BCM or CCM could yield the smaller net volume. This paper proposes a method to estimate the volume ratio for magnetic parts, between single-phase CCM and multiple interleaved BCM power converters as a function of the number of phases, inductor loss, and switching frequency. The results obtained can be applied to boost, forward, and flyback dc-to-dc topologies.

Optimized Parameter Extraction Method for Photovoltaic Devices Model

A model that accurately reproduces the electrical behavior of photovoltaic (PV) devices becomes relevant, not only for cell, panel, array and system simulation, but also as an analysis tool that provides an insight of the internal physical mechanisms of PV devices. Consequently, a method based on genetic algorithms is proposed in this paper to obtain the parameters of the one-diode model of PV cells. The proposed method is applicable to I-V curves at several irradiation and temperature levels. Moreover, it simplifies the computation by adjusting the real data to the modeled one, without solving the transcendental equation that describes the current-voltage (I-V) characteristic. Additionally, the presented method combines two approaches; on the one hand, one that relies on the use of fitting algorithms that minimize the error for the entire set of data, and on the other, one that seeks minimization in selected I-V points (open-circuit, short-circuit and maximum power points ). In order to verify the validity of the method, an I-V curve is obtained out of the parameters previously determined and later compared with that offered by the panel manufacturer.

Steady state characterization of current ripple in DCM interleaved power converters

Power converters that operate in Discontinuous Conduction Mode (DCM) are able to reduce switching losses, when compared to Continuous Conduction Mode (CCM) operation. This reduction is mainly due to zero current commutation and the reduction of the reverse recovery losses. However, DCM operation in high power converters is limited due to the increment in current ripple, which increases losses and volume in the differential mode (DM) filter. Multiphase DCM power converters can reduce total ripple by dividing total current among N phases and interleaving its ripples. Nevertheless, magnitude of ripple reduction as a function of the system parameters has not yet been completely determined. This information would be an important performance indicator and a useful tool for aiding in the design of key converter features, such as the number of phases and DM filter design, in order to meet total ripple, losses or electromagnetic interference specifications. In this sense, this paper proposes a methodology for the steady state characterization of input and output ripple in both buck and boost converters operating in DCM. Experimental tests on a 4-phase buck converter validate the proposal.

Optimized Switching Sequence for Multiphase Power Converters Under Inductance Mismatch

Multiphase power converters allow to reduce semiconductor stress and to improve total ripple characteristics, when compared to a single-phase converter. Semiconductor stress is reduced by dividing the total current among the N parallel-connected converters or phases. Furthermore, total ripple amplitude is reduced and its frequency increases to N times the switching frequency by interleaving each phase current ripple, which lessens the requirements on the total current filtering. These improvements, however, are detrimented mainly by mismatches among the phase inductors value, leading to different ripple amplitudes among phases. As a consequence, when compared to the ideal case, total ripple amplitude is increased, ripple cancellation points are lost, and switching frequency component and its N-1 harmonics are generated. This letter proposes a method to mitigate this problem by selecting the phase switching sequence, in converters operating in the continuous conduction mode, which minimizes the switching frequency component and its harmonics in the total ripple. The proposed method efficiently finds the proper switching sequence for any number of phases, by using a previously presented current ripple characterization as the objective function for the optimization procedure. Simulations validate the proposal and show the improvement, when compared to another strategy present in the literature, which uses the switching sequence modification principle.

Current Ripple Amplitude Measurement in Multiphase Power Converters

Improvements in the total current ripple in interleaved power converters are mainly determined by differences between the phase inductor values. Several methods have been presented in the literature to mitigate this problem, which requires the knowledge of the relative current ripple amplitude. However, in these methods, the measurement of such an amplitude is not addressed. This characteristic is difficult to measure because of the switching noise and the necessity to precisely locate the current waveforms peaks, despite the switches and drivers delay. Furthermore, the above-mentioned methods either perform the correction in real time or in a self-commissioning state. Therefore, it is necessary to implement the amplitude measurement in the same platform as the current control, which implies that the computational overhead should be minimized. This work presents a methodology for the measurement of the ratio among phase current ripple amplitudes in the frequency domain. The proposal allows us to precisely determine this characteristic, with a reduced sampling frequency and high noise immunity. Experimental tests on a four-phase buck converter validate the proposal.