Condition Monitoring Of Capacitors Research Articles

A High-Accuracy Capacitor Condition Monitoring Scheme at Low Sample Frequency Based on Improved Current Reconstruction Method

A High-Accuracy Capacitor Condition Monitoring Scheme at Low Sample Frequency Based on Improved Current Reconstruction Method

Capacitor Condition Monitoring Method for Low-Capacitance StatComs: An Online Approach Using the Inherent Second-Harmonic Oscillations

The cascaded H-bridge low-capacitance static compensator (LC-StatCom) deliberately reduces the capacitor size while allowing large oscillations in capacitor voltages. When a capacitor deteriorates, its capacitance decreases or/and its equivalent series resistance (ESR) increases, compromising StatCom performance and safety. For this reason, the condition monitoring of the capacitors is important to schedule maintenance before failure. This letter introduces a cost-effective and nonintrusive method to monitor the condition of capacitors online. The proposed method offers real-time monitoring without requiring additional hardware or signal injection. The method uses averaged low-frequency signals instead of instantaneous high-frequency signals that can be corrupted by undesired high-frequency noise. Specifically, the method takes advantage of the inherent twice-fundamental-frequency oscillations on the capacitor voltage and current to identify the ESR and capacitance values. The method takes into account the influence of antialiasing filters required for sampling process. The letter shows experimental results that validate the fast and accurate performance of the proposed capacitor condition monitoring.

A Comprehensive Method for Online Switch Fault Diagnosis and Capacitor Condition Monitoring of Three-Level T-Type Inverters

Capacitors and semiconductor power devices are the most fragile components in power electronic systems. Hence, designing a comprehensive method for online switch fault diagnosis (FD) and capacitor condition monitoring (CM) is conducive to guaranteeing the reliability of the three-level T-type (3L-T) inverter in an all-around way. First, based on modeling the 3L-T inverter on the dc link and ac side, the inherent harmonic components of the dc link under normal and open-circuit faults conditions are analyzed. Furthermore, the capacitor current reconstruction method is designed. Subsequently, a comprehensive FD and CM framework is proposed, which consists of signal injection, extra hardware, 3L-T model, FD, and CM submodule. In FD, the detection variable, which is the function of output current and its changing rate, is designed, and the fault location is carried out based on the phase current residual and the sum of the neutral-point voltage residual. The capacitance estimation method is introduced based on the input current reconstruction technology and recursive least squares algorithm using the inherent or injected ac component on the dc link. Finally, experimental results demonstrate that the proposed comprehensive method merits high estimation accuracy, fast dynamic response, and better FD performance under various conditions.

A Capacitance Estimation Method for DC-Link Capacitors Based on Pre-Charging Model and Noise Evaluation

DC-link capacitor is one of the significant parts of traction converters. Due to the impact of electrical stress, high temperature and humidity, its capacitance degrades faster than expected. Accurate capacitance estimation is critical to the condition monitoring of DC-link capacitors, which is also the basis of online capacitor life prediction. Currently, there is a big challenge for capacitor capacitance estimation in railway applications. The noise fluctuation of the voltage sensor may be nearly equal to that of ripple voltage, leading to the considerable errors of the existing capacitor condition monitoring methods. Therefore, a capacitance estimation method based on pre-charging model and noise evaluation is proposed in this paper. The capacitance is estimated by improved recursive extended least square (RELS). The influence of the noise can be effectively reduced and both the calculation accuracy and convergence speed can be well guaranteed through an independent noise estimation model. The proposed method has good immunity in a certain range of signal-noise ratio (SNR) or signal bias. It shows good performance in experiments.

Wavelet-based estimation method for online condition monitoring of dc-link capacitors of distributed energy resources

This paper proposes a novel capacitor condition monitoring for dc-link of power converters employed in distributed energy resources systems. It follows the active methodology, in which an intermittent noncharacteristic signal is injected into the dc-link to estimate the equivalent series resistance (ESR) and capacitance (C) of dc-link capacitors. A real-time stationary discrete wavelet packet transform (RT-SDWPT) performs the capacitor parameter estimations. In this scheme, an interharmonic is used as a noncharacteristic signal to prevent the influence of the system’s inherent harmonic components, mitigating estimation errors. Moreover, the interharmonic frequency is chosen in the region influenced by the ESR and C parameters to ensure capacitor degradation condition. Besides, to mitigate quality issues, the interharmonic’s amplitude, duration, and the time interval between two signal injections follow the recommendations defined by standards. Furthermore, a parameter deviation detection scheme is employed to adaptively adjust the time interval between two estimations, improving failure detection. Experimental results obtained from a microgrid laboratory setup demonstrate the effectiveness and feasibility of the proposed method.

Capacitor Condition Monitoring for Modular Multilevel Converter Based on Charging Transient Voltage Analysis

This article proposes a capacitor condition monitoring (CM) method for modular multilevel converter (MMC) in motor drive applications. The proposed method is based on wavelet decomposition of transient voltage signals, which is independent of modulation schemes and control strategies. The equivalent series resistance (ESR) change can be detected with a moderate computation requirement. Both simulation and experimental results have verified the performance of the proposed method.

A Hierarchic Capacitor Condition Monitoring Strategy for High-Voltage Modular Multilevel Converters

The capacitor condition monitoring is an important issue for the reliable operation of modular multilevel converters (MMCs) in high-voltage applications. The numerous capacitors make the monitoring for the capacitor condition complex and computation-consuming. This paper proposes a hierarchic capacitor condition monitoring strategy to assure the reliability of high-voltage MMCs. In the strategy, the switching times of the switching signals are counted to detect the condition of the capacitor in each submodule (SM). Then, the subsequent capacitance calculation method is only conducted to the abnormal capacitors indicated by the above condition detection algorithm. Meanwhile, the variations of the measured and reference capacitor voltages are employed to calculate the capacitance in the proposed method. The condition detection algorithm shrinks the scope where the abnormal capacitors locate, which avoids calculating the total capacitances in MMCs. In the proposed capacitance calculation method, the complex operations are further saved. Both the two measures reduce the computation burden effectively. The implementation of the whole monitoring strategy is simple and fit for high-voltage MMCs. Moreover, the strategy has no adverse influence on the normal operation of MMCs. The effectiveness of the proposed strategy is verified by the simulation studies with the professional tool Matlab/Simulink.

Capacitor Condition Monitoring for the Low-Capacitance StatCom: An Online Approach

The cascaded H-bridge low-capacitance static com- pensator (LC-StatCom) uses relatively small capacitors subjected to large voltage oscillations. When a capacitor degrades, its capacitance differs from the nominal value, and this deteriorates the StatCom operation and safety. This is an important reason to monitor the capacitors condition in StatComs. This letter presents a detailed analysis of the capacitor voltage oscillations and their dependence on the capacitance values. The analysis allows monitoring the condition of the capacitors using a closed- loop approach that feedbacks the error in voltage oscillations. The proposed method is a hardware-free online solution for ca- pacitor condition monitoring (CCM) in LC-StatComs. The letter presents simulation and experimental results that corroborate the effectiveness of the proposed CCM loop.

An Overview of Condition Monitoring Techniques for Capacitors in DC-Link Applications

Capacitors are widely used in dc links of power electronic converters to balance power, suppress voltage ripple, and store short-term energy. Condition monitoring (CM) of dc-link capacitors has great significance in enhancing the reliability of power converter systems. Over the past few years, many efforts have been made to realize CM of dc-link capacitors. This article gives an overview and a comprehensive comparative evaluation of them with emphasis on the application objectives, implementation methods, and monitoring accuracy when being used. First, the design procedure for the CM of capacitors is introduced. Second, the main capacitor parameters estimation principles are summarized. According to these principles, various possible CM methods are derived in a step-by-step manner. On this basis, a comprehensive review and comparison of CM schemes for different types of dc-link applications are provided. Finally, application recommendations and future research trends are presented.

Online Noninvasive Technique for Condition Monitoring of Capacitor in Linear Power Supplies

Linear power supplies (LPSs) are widely used in fields including measurement systems, radiofrequency systems, medical applications, nuclear power plants, and spacecraft electronics. Electrolytic capacitors are used in a variety of devices because of their small size, low cost, and large capacity. During the use of electrolytic capacitor, it is very common for the capacitance (C) to decrease and its equivalent series resistance (ESR) to increase, which are typical indicators of capacitor degradation. Electrolytic capacitors are both the weak link and the core component of the LPSs and play a vital role in determining the LPSs lifetime. Under the power frequency condition, the power frequency transformer plays a role in isolation and voltage reduction in the LPSs. The input and output signals of the LPSs are used for condition monitoring of capacitor, and the existence of transformer increases the difficulty of the online noninvasive technique of LPSs. The online noninvasive technique for condition monitoring of capacitor in LPSs proposed in this article can be solved only by using the input current, the magnetizing current, the input voltage, and the load current. Effect of temperature on C and ESR values is incorporated for accurate determination of the parameters of capacitor. The effectiveness of the proposed method is verified through simulations and experiments, and the data obtained are consistent with the results measured using an LCR meter.

Switching Signals Based Condition Monitoring for Submodule Capacitors in Modular Multilevel Converters

The capacitors are one of the most important com- ponents in modular multilevel converter (MMC). Due to the large numbers of capacitors applied in MMC, the primary technical challenge about the capacitors is reliability. To identify the abnormal capacitors and improve the performance of MMCs, the capacitor condition monitoring strategy is proposed in this brief. In the monitoring algorithm, the relationship of the capacitances in an arm is deduced. The actual and nominal sums of switching signals for submodules (SM) are used to estimate the capacitances. Furthermore, a compensation for dead time is added to enhance the monitoring accuracy. The proposed condition monitoring algorithm not only simplifies the calculation of capacitances with high accuracy, but also has no adverse influence on the normal operation of MMCs. The feasibility of the proposed strategy is verified by the simulation results in MATLAB/Simulink.

A Reference Submodule Based Capacitor Condition Monitoring Method for Modular Multilevel Converters

This letter proposes a novel capacitor condition monitoring method for modular multilevel converters (MMCs) based on reference submodules (SMs). It significantly enhances the capacitor monitoring accuracy by making full use of the SM voltage sensor measurement range. Accuracy comparison between the existing method and the proposed method is conducted to quantify the improvement of accuracy. Moreover, its operation principle and practical implementation considerations are presented. Finally, a three-phase MMC platform is built to experimentally verify the effectiveness of the proposed method.

Capacitor Condition Monitoring Based on the DC-Side Start-Up of Modular Multilevel Converters

This letter proposes a new submodule capacitor condition monitoring method for modular multilevel converters (MMCs) based on the dc-side start-up procedure. During this process, the MMC can be simplified into an RC charging circuit, and the submodule capacitance can be estimated by investigating its relationship with the phase current and submodule voltage. Several practical issues related to the implementation, advantages, and limitations of the proposed method are presented as well. In order to validate the method, a series of experiments with different submodule capacitances are conducted based on a three-phase MMC platform. Experimental results confirm the effectiveness and feasibility of the proposed method.

High-Accuracy Capacitance Monitoring of DC-Link Capacitor in VSI Systems by LC Resonance

Monitoring the condition of a dc-link capacitor is important for the reliability-critical voltage source inverter (VSI) systems. With the ever increasing application of a metalized poly propylene film (MPPF) capacitor, a new challenge for dc-link capacitor condition monitoring (CM) is presented due to the very small equivalent series resistance and capacitance end-of-life criterion (typically 2%–5%) of an MPPF capacitor. To improve the accuracy of capacitance estimation, a novel quasi-online CM method is proposed in this paper, which introduces an LC resonance intentionally when system is not in operation. Experimental work is carried out to validate the method and the results show that 1% capacitance estimation accuracy can be achieved in a 3-kW induction machine variable frequency drive system. Because of the signal measurement at large amplitude (e.g., nominal current) and the time-based multi-parameters identification algorithm, the method is accurate and inherently insensitive to the system parameters variation, measurement noise, and effect of temperature drift. In practice, the method can be implemented using the system available sensors with no need of hardware modification. Moreover, since the resonance current is limited and decays shortly, the condition of a dc-link capacitor can be monitored safely and frequently on-site in a VSI system.

Condition Monitoring of DC-Link Capacitors Using Goertzel Algorithm for Failure Precursor Parameter and Temperature Estimation

Aluminum electrolytic capacitors are some of the weakest components in a power converter system. Therefore, condition monitoring of capacitors can prevent unexpected system downtime due to capacitor failures. This article proposes a condition monitoring system for electrolytic capacitors used as dc-link capacitors in front-end rectifier-fed three-phase inverters. The proposed methodology is based on equivalent series resistance (ESR) and capacitance estimation using the Goertzel algorithm. The ESR is used as the degradation indicator, whereas the capacitance value is used as both degradation indicator and temperature-sensitive electrical parameter to estimate core or hotspot temperature. Even though the use of capacitance to estimate hotspot temperature has already been proposed, this article tackles the practical difficulties associated with capacitor core-temperature estimation using the capacitance and demonstrates a successful implementation strategy for applying this method in power converters to estimate core temperature online. It also introduces a self-calibration procedure to mitigate ageing-related errors in temperature estimation. An experimental setup is used to verify the proposed conditioning monitoring system. The experimental results prove the effectiveness and accuracy of the proposed technique.

Online Condition Monitoring System for DC-Link Capacitor in Industrial Power Converters

This paper proposes an online condition monitoring system for aluminum electrolytic capacitors used as dc-link capacitors in industrial power converters. Electrolytic capacitors are one of the most fragile components of a power converter system because of their wear-out failures and short lifespan. Therefore, the use of condition monitoring systems for aluminum electrolytic capacitors allow preventive maintenance to be performed, thereby avoiding unexpected shutdown and downtime. The dominant wear-out mechanisms in aluminum electrolytic capacitors are characterized by the increase in equivalent series resistance. Hence, the condition monitoring system proposed in this paper is based on the online estimation of the capacitor's equivalent series resistance using the switching frequency components of the dc-link capacitor voltage and current. The equivalent series resistance estimation method is tested using the PSpice circuit simulator and is validated experimentally using a custom-made inverter. Finally, the equivalent series resistance estimation method is adapted for the condition monitoring of capacitors in industrial power converters and the proposed condition monitoring system is implemented in a commercial ac drive system to prove the applicability of the proposed method to industrial power converters.

A Review of the Condition Monitoring of Capacitors in Power Electronic Converters

Capacitors are one type of reliability-critical components in power electronic systems. In the last two decades, many efforts in academic research have been devoted to the condition monitoring of capacitors to estimate their health status. Industry applications are demanding more reliable power electronics products with preventive maintenance. Nevertheless, most of the developed capacitor condition monitoring technologies are rarely adopted by industry due to the complexity, increased cost, and other relevant issues. An overview of the prior-art research in this area is therefore needed to justify the required resources and the corresponding performance of each key method. It serves to provide a guideline for industry to evaluate the available solutions by technology benchmarking, as well as to advance the academic research by discussing the history development and the future opportunities. Therefore, this paper first classifies the capacitor condition monitoring methods into three categories, then the respective technology evolution in the last two decades is summarized. Finally, the state-of-the-art research and the future opportunities targeting for industry applications are given.

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).