Aluminium electrolytic capacitors (AECs) are used in dc-link of single-phase grid connected solar photovoltaic (PV) inverters to suppress the dc-link voltage oscillation. With aging its capacitance decreases and equivalent series resistance (ESR) increases, which may lead to increase in voltage ripple, thereby reducing average power extracted from solar PV and/or damage the semiconductor switches due to overvoltage. Further, prolonged use of the aged capacitor could lead to the open circuit of the dc-link due to vaporization of the electrolyte. Therefore, to enhance the reliability of the system by predictive maintenance, it is necessary to monitor the health of AEC. A quasi-online method for condition monitoring of the AECs in solar inverters is proposed in this paper. This method is active during the night when there is no solar irradiance. In this case, the current of various odd harmonic frequencies are injected by the inverter and dc-link capacitor impedances at various frequencies are evaluated. Using these impedance values, least mean square algorithm is used to estimate the ESR and capacitance values. The magnitude of each injected harmonic current is kept within the limits prescribed by IEEE 929-2000 standard. The key advantage of the technique is that it combines the estimation of both ESR and capacitance to determine the health. Further, it does not require significant processing capability and is implemented in the existing digital processor/controller used for inverter control. Detailed simulation studies are carried out using MATLAB-Simulink. Proposed scheme is verified experimentally on a scaled down version of a grid connected solar inverter. Puncturing based technique is used for accelerated aging of the capacitor. Estimated values of ESR and C are in agreement to that measured from LCR meter.

Quasi-Online Technique for Health Monitoring of Capacitor in Single-Phase Solar Inverter

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Heat Transfer Thermal Management Of Electronics

Lifetime is an important performance factor in the reliable operation of power converters. However, the state-of-the-art LC filter design of a buck dc–dc converter is limited to the specifications of voltage and current ripples and constrains in power density and cost without reliability considerations. This paper proposes a method to optimize the design of the LC filters from a reliability perspective, besides other considerations. An enhanced model is derived to quantify the lifetime of the capacitor in the filter considering the electrothermal stress on it. Furthermore, the influence of different design aspects such as the value of capacitance, the value of inductance, and the type of the capacitor have been discussed, focusing on their impacts on the key design objectives, which are the cutoff frequency, lifetime, and volume. Based on the analysis, an optimized design is proposed among different parameter sets. A 1-kW converter prototype is applied to verify the theoretical analysis and simulation.

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Reliability-Oriented Optimization of the LC Filter in a Buck DC-DC Converter

Lifetime investigation and prediction of metallized polypropylene film capacitors

Since electrolytic capacitors are primarily responsible for breakdowns in power electronics converters and have the trait of high failure rate, their reliability is a tremendous concern. Consequently, an appropriate monitoring as well as fault diagnosis system should be laid emphasis on. In this paper, an original and accurate online scheme applied to estimate the output capacitor of the flyback converter is put forward. By analyzing the voltage ripple of the output electrolytic capacitor in detail, an online mathematical model for the equivalent series resistance (ESR) and capacitance (C) is derived. A trigger circuit and an isolated amplification circuit are designed to catch the output voltage ripple values at certain instants of switching cycle, which are sent to digital signal processor for the calculation of ESR and C. The proposed scheme is noninvasive as no extra current sensor is needed. In order to verify the feasibility of the scheme, a prototype of the online monitoring system is built and experiments are conducted.

Noninvasive Online Condition Monitoring of Output Capacitor’s ESR and C for a Flyback Converter

Being reliability critical components, and widely used in electronics today, electrolytic aluminum capacitors are one of the most likely components to fail under extreme working conditions. Therefore in safety critical applications, their lifetime prediction is of vital importance. The following paper analyses current prediction algorithms and offers an improved solution for capacitor lifetime prediction. The results are obtained from accelerated ageing tests and theoretical data obtained from calculi are compared to real world data obtained from measurements.

Accelerated ageing tests for predicting capacitor lifetimes

As electronic modules are becoming ever more popular in critical safety applications, such as electronic vehicles and aeronautics, so do their operating conditions become harsher. This sometimes means using electronic components at the very limit of their functional parameters and very close to or even exceeding their maximum operating temperature. This of course leads to a dramatic decrease in component lifetimes and classical failure prediction algorithms are thrown off balance, giving unreliable results. This of course means that new prediction methods should be established. The following paper proposes a method for predicting the value of capacitors on the electronic modules, in order to perform real-time prediction of their lifetimes affected by their operational environment. First, two capacitor lifetime models are presented and compared and then the theoretical data are compared with the data obtained from accelerated ageing measurements.

Parameter monitoring of electronic circuits for reliability prediction and failure analysis

Thermal management in electronics continues to be one of the most important fields which can take part in ensuring the reliability of an electronic system. Heat transfer, from a system to the ambient, must be optimized, and even a temperature with 1°C less can have an effect in prolonging the life of an electronic component. The research presented in this paper aims to decrease the junction temperature of a power device, by optimizing the placement of thermal vias underneath the IC. Various thermal vias placement scenarios are analyzed and their benefit in improving the thermal dissipation from a component to the PCB and ambient is discussed.

Thermal via placement for high-power applications

The main purpose of this paper is to present a software implementation referring to an indirect Tire Pressure Measurement System (iTPMS) based on the Anti-lock Braking System (ABS) present in a car. The novelty of the research is the achievement of a Simulink car model which is able to feed simulated data consistent with real-life measurements to the hardware system for functional testing of the implemented measurement method, without the need of an actual car and road test. An additional Android application is implemented for the purpose of helping the driver to determine and solve the problem stated by the possibility of appearance of tire under inflation.

Implementation of a car model for indirect tire pressure monitoring system

The influences of different soldering methods and specific thermal profiles were investigated on the lifetime of through hole capacitors. The behavior of aluminum electrolytic, ceramic and two capacitor types with different plastic dielectric capacitors were evaluated when using alternative soldering methods instead of the standard wave soldering process, such as vapour phase or infrared convection. The changes in the values of capacitance and ESR of the capacitors were monitored before and after soldering and the influence of the different techniques on their lifetimes was assessed.

Rajmond Jano

Papers

Accelerated ageing tests for predicting capacitor lifetimes

Parameter monitoring of electronic circuits for reliability prediction and failure analysis

Thermal via placement for high-power applications

Implementation of a car model for indirect tire pressure monitoring system

Effects of reflow soldering methods on the lifetime of capacitors