A.M.R. Amaral

An Online and Noninvasive Technique for the Condition Monitoring of Capacitors in Boost Converters

Capacitors usually determine the overall lifetime of power converters since they are mainly responsible for breakdowns. Their failure results from the deterioration of their dielectric, the production of gases, and, eventually, their explosion. This process leads to an increase in the capacitor equivalent series resistance (ESR) and a decrease in its capacitance value for both electrolytic and metalized polypropylene film (MPPF) capacitors. In this paper, a novel noninvasive technique for capacitor diagnostic in Boost converters is presented. It can easily be applied online and even in real time, and it is suitable for the operation in both continuous current mode (CCM) and discontinuous current mode (DCM). The technique is based on the double estimations of the ESR and the capacitance, improving the diagnostic reliability. This way, predictive maintenance is provided, and it is possible to alarm for capacitor replacement, avoiding downtime. As the method is intended for railway high-power applications, it has been conceived neither to add any additional hardware in the power stage nor to even slightly modify it. To demonstrate and validate the effectiveness and accuracy of the proposed technique, several simulations and experimental results are discussed in a small prototype. In this prototype, the software for real-time estimation is programmed in a low-cost digital signal processor (DSP).

A Simple Offline Technique for Evaluating the Condition of Aluminum–Electrolytic–Capacitors

This paper presents a very simple technique to estimate the condition of aluminum-electrolytic-capacitors. The aging of aluminum-electrolytic-capacitors is expressed by the increase of their equivalent series resistance (ESR) and the reduction of their capacitance. Thus, the proposed technique is based on the estimation of both the ESR and capacitance values. To implement the proposed technique, the capacitor is fed by a sinusoidal voltage with the required power. The resultant impedance vector defined by the capacitor voltage and current gives enough information to estimate the condition of the capacitor.

Use of ESR to predict failure of output filtering capacitors in boost converters

This paper addresses the subject of fault diagnosis in boost converters, operating in continuous and in discontinuous mode, focusing particularly, in the output filtering electrolytic capacitors. The failure of those capacitors leads to an increase of their equivalent series resistance (ESR), and therefore, the efficiency decreases and the output voltage ripple increases. Two diagnostic methods are used, one is based on the relation between the mean values of the output voltage ripple and of the capacitor current ripple, both considered during the conduction time of the transistor, and the other is based on the relation between the value of the output voltage ripple for Ton/2 and the mean value of the output current. Several simulated and experimental results are presented for two DC-DC boost-type converters, one operating in the continuous mode and the other in the discontinuous mode.

An Experimental Technique for Estimating the ESR and Reactance Intrinsic Values of Aluminum Electrolytic Capacitors

This paper presents an experimental technique that allows the determination of the reactance and ESR intrinsic values of aluminum electrolytic capacitors. The equivalent circuit of an electrolytic capacitor comprises an equivalent series inductance (ESL), an equivalent series resistance (ESR) and a capacitance (C), whose values change with frequency. Therefore, the behavior of an electrolytic capacitor varies from approximately a simple capacitor for low frequencies, to a resistor at its resonance frequency, and finally to an inductor for frequencies higher than its resonance frequency. The knowledge of the resonance frequency of the electrolytic capacitors, as well as their equivalent circuit at the operating frequency becomes of paramount importance for designing purposes. The ESR is one of the most critical problems of static converters that operate near the resonance frequency of the electrolytic capacitors. An increased ESR value leads to a significant increase in the alternate component of the output voltage, requiring a constant action of the control system. To validate the proposed technique and to demonstrate its applicability some experimental and simulated results are presented

Condition Monitoring of Metallized Polypropylene Film Capacitors in Railway Power Trains

A novel technique for monitoring the condition of metallized polypropylene film (MPPF) capacitors installed in the dc link of railway power trains is proposed in this paper. The technique is based on the capacitance estimation of the two different capacitors used in the dc link (dc filtering and 2F filter capacitors), and it is done without adding any extra sensor or filter to the respective traction drive scheme. Therefore, the proposed method is implemented using software but not additional hardware for the different trains. Two other important passive component parameters of the traction drive are also monitored, all of them by means of curve fitting based on the least-mean-square (LMS) algorithm. The proposed technique is implemented and validated at simulation and experimental levels, using MATLAB/Simulink and a 1.2-MW traction drive test bench. Very accurate results are obtained, and the predictive maintenance of MPPF capacitors for different topologies of railway power trains can be set through the proposed technique.

Parameter Estimation of a DC/DC Buck converter using a continuous time model

In this paper, a novel online technique for estimating the parameters of a DC/DC buck converter through a continuous time model is proposed. Standard least mean squares algorithm is applied among other formulations, taking into account only the non conduction state during a single switching cycle. The problem of derivative calculation of the needed voltage and current signals is solved by polynomial interpolation.

Using input current and output voltage ripple to estimate the output filter condition of switch mode DC/DC converters

This paper presents a fault diagnostic technique that is able to estimate the output filter condition of DC/DC boost and buck-boost converters. More than half of the breakdowns in these equipments are mainly due to the output filter capacitor. So, the development of fault diagnostic techniques that can avoid unexpected breakdowns is of paramount importance. The aging of the output filter capacitors is expressed by the increase of their internal resistance, that changes considerable with temperature. The proposed technique uses both input current and output voltage ripple to estimate capacitors internal resistance; for that, a very simple analytical relationship between both waveforms is used. The temperature effect is also considered for evaluating the capacitors condition.

An Online Technique for Estimating the Parameters of Passive Components in Non-Isolated DC/DC Converters

In this paper, a novel online technique used for estimating the parameters of passive components in non-isolated DC/DC converters is presented. The technique is implemented for the boost and buck-boost converters, operating both in continuous current mode (CCM) and discontinuous current mode (DCM). The technique is based on the sampling of the MOSFET gate signal, inductor current and load voltage, which is followed by the processing of the acquired data through different ways such as the least mean squares algorithm. The knowledge of these passive components parameters may be used in the fault diagnosis of such converters. Results obtained from simulations are presented, followed by experimental results in which the inductance, capacitance, load resistor and ESR of the capacitor are estimated, in order to validate the proposed technique.

An automatic technique to obtain the equivalent circuit of aluminum electrolytic capacitors

This paper presents an economic and automatic experimental technique that allows the determination of the equivalent circuit of aluminum electrolytic capacitors at their operating conditions. The equivalent circuit of an electrolytic capacitor comprises an equivalent series inductance (ESL), an equivalent series resistance (ESR) and a capacitance (C). Both C and ESR values change with frequency, temperature and aging. The knowledge of the capacitor ESR value is essential to achieve the best design proposal for switch mode power supplies (SMPS) and in the selection of the best capacitors used in the DC link of adjustable speed drives (ASD). On the other hand, the accurate knowledge of the capacitor capacitance is also very important in the rectifiers design and in the choice of the best capacitor for the DC link of ASD. Moreover, the knowledge of both parameters allows the evaluation of the capacitor state condition. To implement the proposed technique, two distinct circuits should be considered. The first one accounts for the estimation of the ESR and reactance of the capacitor, while the second one allows the estimation of the capacitor capacitance. To implement the first circuit, it is necessary to put the capacitor under test in series with a resistor and connect them to a sinusoidal voltage. The relationship between the gain and phase of the capacitor voltage and current waveforms, obtained from sinusoidal fitting, gives enough information to compute both ESR and reactance of the capacitor. The second circuit is a simple charge/discharge circuit. From the relationship between the capacitor current and voltage, during discharge, it is possible to compute its capacitance using the least mean square algorithm.

ESR Estimation Method for DC/DC Converters Through Simplified Regression Models

In this paper, simplified regression models useful for parameter extraction are obtained from the hybrid models of Buck and Boost DC/DC converters. These models are used in the ESR estimation of output filter capacitors present in the same circuits for diagnostic purposes. Advantages obtained through the simplified models are outlined regarding the original complete regression models obtained from the respective hybrid models. The simplified and the original parameter estimation methods are both applied and compared between them regarding accuracy, data processing time and reliability of the implemented algorithms. Results obtained from simulations and experimental results are presented.