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Zhaoyang Zhao

Other affiliations: Zhengzhou University
Bio: Zhaoyang Zhao is an academic researcher from Chongqing University. The author has contributed to research in topics: Buck converter & Transient (oscillation). The author has an hindex of 5, co-authored 13 publications receiving 68 citations. Previous affiliations of Zhaoyang Zhao include Zhengzhou University.

Papers
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Journal ArticleDOI
TL;DR: A comprehensive review and comparison of CM schemes for different types of dc-link applications with emphasis on the application objectives, implementation methods, and monitoring accuracy when being used is provided.
Abstract: 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.

98 citations

Journal ArticleDOI
TL;DR: An online monitoring scheme is proposed for buck converters, aiming to estimate the ESR and capacitor parameters of AEC at the output side using large-signal load transient trajectories and has a relatively low sampling frequency.
Abstract: Aluminum electrolytic capacitor (AEC) is one of the weakest components in power electronic converters. As the degradation of AEC happens, its equivalent series resistance (ESR) increases and the capacitance ( $C)$ decreases. Therefore, the online monitoring of ESR and $C$ to predict AEC’s life has great significance for ensuring safe and reliable operation of converters. In this article, an online monitoring scheme is proposed for buck converters, aiming to estimate the ESR and $C$ of AEC at the output side. The proposed scheme utilizes large-signal load transient trajectories to estimate the AEC parameters and has a relatively low sampling frequency. By analyzing the relationship between the transient trajectory and capacitor parameters, the ESR is directly calculated using the voltage and current step values at the initial instant of the transient. Furthermore, $C$ is calculated utilizing a calculation model derived from the output-voltage load transient trajectory. Corresponding simulation analysis and an online monitoring system implementation are provided. Furthermore, a 48–12-V buck converter with a digital proportional-integral (PI) controller and an analog $V^{2}$ controller is built to verify the proposed online estimation method. The experimental results of the estimated ESR and $C$ are consistent with the results measured by an LCR meter, and the estimation error is less than 10%.

34 citations

Journal ArticleDOI
Weiguo Lu1, Xuemei Lu1, Jinxin Han1, Zhaoyang Zhao1, Xiong Du1 
TL;DR: In this paper, an online ESR estimation method of aluminum electrolytic capacitor (AEC) was proposed by using the wavelet transform (WT) based time-frequency analysis, and the relationship between ESR and the jump amount of output voltage at turn- off moments was analyzed first, and then the ESR calculation model was derived using WT with the Wavelet basis of the first derivative of Gaussian function.
Abstract: Aluminum electrolytic capacitor (AEC) is one of the most age-affected components in ac–dc conversion, and its equivalent series resistance ( ESR ) is an important index for reflecting the healthy condition of AEC. In AEC-used boost power factor correction (PFC) converters, ESR of AEC causes a small jump in the switching ripple of output voltage at switching moments, especially at turn- off moments. This small jump is hardly observed at line-frequency scale, either using time-domain analysis or frequency-domain analysis. However using time–frequency analysis this jump is very prominent due to its singularity. In this article, an online ESR estimation method of AEC is proposed by using the wavelet transform (WT) based time–frequency analysis. The relationship between ESR and the jump amount of output voltage at turn- off moments is analyzed first, and then the ESR calculation model is derived using WT with the wavelet basis of the first derivative of Gaussian function. An appropriate sampling interval for the output voltage and the inductor current is determined. Besides, the online ESR estimation scheme is implemented including the hardware and software designs. Furthermore, a prototype of boost PFC converter with 220 V ac input and 360 V dc output is built, where an average current mode control chip UC3854 is used. Four factors are discussed for estimation accuracy in the experiment, and the estimated results are consistent with the results measured by LCR meter with a relative error less than 10%.

26 citations

Journal ArticleDOI
TL;DR: A current feedforward scheme in the inner-current loop to remove the LPF is proposed, where the harmonic distortion of the reference current is suppressed by using a current-harmonic feedforward compensation way in synchronous reference frame.
Abstract: In boost power factor correction (PFC) converters, a low-pass filter (LPF) is generally adopted to eliminate the influence of the double-line frequency output voltage ripple on the controlled input current, which, therefore, limits the outer-voltage loop bandwidth. Different from the existing alternative schemes to the LPF, which eliminate the influence of the output voltage ripple using output-feedback ways in the outer-voltage loop, this article proposes a current feedforward scheme in the inner-current loop to remove the LPF. In the proposed scheme, the harmonic distortion of the reference current is suppressed by using a current-harmonic feedforward compensation way in synchronous reference frame. Finally, a 225-W experimental prototype is built with digital implementation, and the experimental results show a more than 68% improvement of the dynamic response for the case with the proposed scheme as compared with the traditional LPF scheme, along with a high-quality controlled current.

19 citations

Journal ArticleDOI
TL;DR: This letter investigates the influence of transients on the damage of capacitors in VRMs using a 150-W VRM as a case study and a suitable capacitor configuration of capacitor banks is provided in order to maximize its lifetime.
Abstract: Capacitors are critical in voltage regulator modules (VRMs), which contribute to store energy and stabilize the output voltage during load transients. Usually, VRMs work with consecutive load transients, which would bring more electrothermal stress to capacitors and affect the reliability of capacitors compared with the steady-state operation. Recently, some efforts have been made to investigate the reliability of capacitors in power electronic converters. Unfortunately, transient processes are commonly ignored, which can impair the accuracy of the lifetime estimation. Regarding this issue, this letter investigates the influence of transients on the damage of capacitors in VRMs. A 150-W VRM is introduced as a case study. First, the electrothermal stresses during steady state and transients are analyzed. Then, the lifetime calculation is considered from a single capacitor to hybrid capacitor banks. In addition, a suitable capacitor configuration of capacitor banks is also provided in order to maximize its lifetime.

18 citations


Cited by
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Journal ArticleDOI
TL;DR: A comprehensive review and comparison of CM schemes for different types of dc-link applications with emphasis on the application objectives, implementation methods, and monitoring accuracy when being used is provided.
Abstract: 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.

98 citations

Journal ArticleDOI
TL;DR: An online monitoring scheme is proposed for buck converters, aiming to estimate the ESR and capacitor parameters of AEC at the output side using large-signal load transient trajectories and has a relatively low sampling frequency.
Abstract: Aluminum electrolytic capacitor (AEC) is one of the weakest components in power electronic converters. As the degradation of AEC happens, its equivalent series resistance (ESR) increases and the capacitance ( $C)$ decreases. Therefore, the online monitoring of ESR and $C$ to predict AEC’s life has great significance for ensuring safe and reliable operation of converters. In this article, an online monitoring scheme is proposed for buck converters, aiming to estimate the ESR and $C$ of AEC at the output side. The proposed scheme utilizes large-signal load transient trajectories to estimate the AEC parameters and has a relatively low sampling frequency. By analyzing the relationship between the transient trajectory and capacitor parameters, the ESR is directly calculated using the voltage and current step values at the initial instant of the transient. Furthermore, $C$ is calculated utilizing a calculation model derived from the output-voltage load transient trajectory. Corresponding simulation analysis and an online monitoring system implementation are provided. Furthermore, a 48–12-V buck converter with a digital proportional-integral (PI) controller and an analog $V^{2}$ controller is built to verify the proposed online estimation method. The experimental results of the estimated ESR and $C$ are consistent with the results measured by an LCR meter, and the estimation error is less than 10%.

34 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present exploratory efforts in the data-driven condition monitoring of power electronic systems (PES) in the view of existing challenges and emerging opportunities using Artificial Intelligence (AI).
Abstract: Condition monitoring is a proactive measure to realize operation optimization, predictive maintenance, and high availability of Power Electronic Systems (PES). It is demanded by reliability-, safety-, or availability-critical applications. The core of condition monitoring is a prediction based on historical and present information. Artificial Intelligence (AI) could play a role in addressing optimization, regression, and classification problems in predicting the operation or health status of PES. Besides AI algorithms, quality data collection, objective formulation, and result validation require an in-depth understanding of the PES. The nexus between PES and AI expects to create overarching effects in the condition monitoring area. This article presents exploratory efforts in the data-driven condition monitoring of PES in the view of existing challenges and emerging opportunities.

34 citations

Journal ArticleDOI
TL;DR: This article introduces the use of the short-time Fourier transform (STFT) technique to determine and track C and ESR values, starting from some always-existing harmonics at low and high frequencies.
Abstract: Faults in aluminum electrolytic capacitors (AECs) are classified as the major cause for power electronics equipment breakdown, mainly due to AECs wear out through the vaporization of the electrolyte, as a result of both aging and temperature effects. The majority of manufacturers identify the end-of-life threshold of such capacitors as their equivalent series resistance (ESR) increases by 80% or their capacitance (C) decreases by 20%, relative to their initial values. Therefore, the online estimation of these two parameters can provide valuable and timely information that allows detecting any potential capacitor failure. Changes in C and ESR parameters influence the relationship between the capacitor voltage and current ripples. This ratio is dominated by C at low frequencies, and by ESR in the high-frequency range. The aim of this article is to propose an algorithm allowing a continuous estimation and tracking of both parameters (ESR and C). This algorithm should be simple, fast, and suitable for online implementation. Therefore, this article introduces the use of the short-time Fourier transform (STFT) technique to determine and track C and ESR values, starting from some always-existing harmonics at low and high frequencies. The STFT is based on applying the discrete Fourier transform algorithm on a sliding window, which makes it more appropriate for online implementation. The effectiveness of the proposed method is proved by simulation and laboratory experiments, using a boost dc–dc converter.

33 citations

Journal ArticleDOI
TL;DR: Pulse train (PT) control strategy for the boost power factor correction (PFC) converter operating in the continuous conduction mode (CCM) is proposed and studied and the dynamic response is significantly improved.
Abstract: Pulse train (PT) control strategy for the boost power factor correction (PFC) converter operating in the continuous conduction mode (CCM) is proposed and studied in this article. Average current mode (ACM) control is usually utilized for the CCM boost PFC converter. The ACM-controlled PFC converter suffers from poor dynamic response, because its voltage control loop has to be designed with low bandwidth to minimize the effect of low-frequency output voltage ripple on the current control loop. Different from ACM control, the voltage control loop and current control loop of the PT-controlled PFC converter are decoupled, and thus the effect of low-frequency output voltage ripple on the current control loop is eliminated. Besides, PT modulation is utilized in the proposed controller to regulate the inductor current to follow the current reference. Thus, both high power factor and fast dynamic response can be achieved. The operation principle of the PT-controlled CCM boost PFC converter is analyzed, and a 300-W prototype is built to verify the analysis results. The experimental results show that power factor of the PT-controlled PFC converter is higher than 0.998 and the dynamic response is significantly improved.

29 citations