Figure - uploaded by Huai Wang
Content may be subject to copyright.
Typical configurations of power electronic conversion systems with dc-link capacitors: (a) ac–dc-dc or dc-dc-ac power converters with a dc link. (b) ac-dc-ac power converters with a dc link. (c) ac-dc or dc-ac power converters with a dc link.
Source publication
![Corrosion of the metallized layers of a film capacitor [23]. (a)...](profile/Huai-Wang-2/publication/265855846/figure/fig1/AS:305474567196703@1449842220780/Corrosion-of-the-metallized-layers-of-a-film-capacitor-23-a-Separation-of-metal-film_Q320.jpg)
DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link d...
Contexts in source publication
Context 1
... APACITORS are widely used for dc links in power converters to balance the instantaneous power difference between the input source and output load, and minimize voltage variation in the dc link. In some applications, they are also used to provide sufficient energy during the hold-up time. Fig. 1 shows the typical configurations of power electronic conversion systems with dc-link capacitors. Such configurations cover a wide range of power electronics applications, such as in wind turbines, photovoltaic systems, motor drives, electric vehicles and lighting systems. With more stringent reliability constrains brought by ...Context 2
... the possibilities brought by innovative dc-link so- lutions, a reliability-oriented design procedure could provide further potentials to build the reliability into the dc link. Fig. 10 presents a reliability-oriented design procedure for dc links. Highlighted areas indicate where further research efforts are expected. The key steps are discussed as ...Context 3
... Thermal analysis and design: As shown in Table II, temperature is one of the most important stressors that influence the reliability of capacitors. Therefore, besides the electrical Fig. 10. Reliability-oriented design procedure for capacitors in dc links. stress analysis [33], thermal stress analysis is equal important to the choice of capacitors and the design of dc-link banks. The connection between the electrical stress analysis and thermal stress analysis is the thermal impedance network of the capaci- tor of ...Context 4
... the above design procedure provides a systematic way to select the dc-link capacitors with optimized cost, size and lifetime, it may be still not easy to be applied since its high level of complexity as well as the needs for further research in some of the key steps highlighted in Fig. 10. Among others, the research effort needed is to develop user-friendly software tools that can implement the procedure, so that the power electronic designers can practically apply it in a much easier ...Context 5
... research work have been done on the condition monitoring of Al-Caps [50]- [54]. Fig. 11 shows the impedance characteristics of capacitors. In the low frequency range (ω < ω 1 ), the impedance is approximated to ωC. In the medium frequency range (ω 1 < ω < ω 2 ), the impedance is dominated by the ESR. Therefore, by extracting the voltage and/or current information in the respective frequency ranges, the capacitance and ESR ...Similar publications
Power electronics plays a key role in electric vehicle technology in areas such as the battery charging and managing, dc distribution and motor drive systems, among others. There are, however, significant challenges to be addressed in terms of cost, performance, reliability and power density. This paper aims at proposing an improved on-board charge...
Capacitors are critical components of power converter systems as they influence the cost, size, performance, and scale of such systems. However, capacitors exhibit the highest degeneration and breakdown rates among all power converter components due to their wear-out failures and short lifespans. Therefore, condition monitoring is a vital process t...
Citations
... the dc power again to ac power of the desired phase, frequency, and voltage amplitude. The major problem with energy storage electrolytic capacitors is that their installation occupies large physical space as compared to the semiconductor devices leading to lower power density [1]. ...
Practical applicability of the single-phase (1∅) power supplied conventional single-stage matrix converter (SSMC) to synthesize multi-phase (m∅) power is limited to very low frequency (3 to 5 Hz) output. In this paper, a modified SSMC is proposed for 1∅
to
m∅ conversion which can extensively operate to derive the output frequency up to half of the rated supply frequency and ensures balanced operation with better power quality across the supply as well as load side. The proposed SSMC is having three branches each constitute of an array of bidirectional switches supplied by a 1∅ source through a filter circuit of one inductor and two capacitors. This configuration of the proposed SSMC make it suitable to synthesize m ∅ output from the available 1∅ power supply from very low output frequency to maximum frequency equals to half of the rated supply frequency while maintaining supply side unity power factor (UPF) and standard voltage transfer ratio (VTR). Experimental results are presented to validate the performance of the proposed SSMC for 1∅
to
m∅ conversion.
... To improve the system's well-being, the reliability evaluation is carried out at different stages: converter level (the focus of this study), component level, and system level. At the component level, [5] gives an overview of reliability factors of various types of capacitors, and a design approach is proposed to improve the capacitor reliability. In [6], authors focus on power semiconductor devices, and reliability aspects of such devices in converter applications are reviewed. ...
Modular Multilevel Converter (MMC) is favorable for high-power grid-connected power electronic applications to achieve efficient operation. The required number of components significantly increases when higher modularity is introduced for the given voltage level, thus reducing the system reliability. This paper suggests a Mixed Redundancy Strategy (MRS) that combines the operational concepts using active and redundant spare sub-modules. It is shown that more than 50 % higher B = 10 lifetime is achievable as compared to reliability improvement using Fixed-Level Active (FL-ARS), Load-Sharing Active (LS-ARS), and Standby Redundancy Strategy (SRS) with the same number of redundant submodules. The trade-off between operational efficiency and investment cost is explored to define the boundary for selecting MRS over other redundancy strategies with varying dc-link voltages and average converter loading considering a 10-year payback period and equivalent B = 10 lifetime. The results are discussed for two case studies using load profiles adapted from available data from a medium voltage substation. The change in viability boundary for MRS is established with increasing B = 10 lifetime and its sensitivity to power electronic component cost as well as assumed failure rate.
... The testing samples (C x ) were placed in a temperature chamber at 60°C for 500 h, where the subscript is related to the applied voltage of the testing sample. The ageing electric voltage conditions are shown in Table 1, where the 50 Hz AC voltage ripple ratios were 12%, 20%, and 28%, representing the functional condition for the capacitor equipment in the flexible DC transmission system, based on the online recorded data of the power system and the reported study [13,14]. A reference capacitor was placed in the same chamber without any voltage and was named as REF. ...
This study focuses on the degradation behaviour of metallised film capacitors, which are the essential components for the stability of converter valves in flexible ultra‐high voltage direct current (HVDC) transmission systems. Through systematic experimentation, we investigated the failure mechanisms of MFCs under HVDC fields with superimposed harmonics, considering both equipment and material perspectives. The experiments subjected capacitors to 500 h of ageing under two conditions: a DC/AC‐superimposed field with a constant DC component of 290 kV/mm and an AC ripple rate varying from 12% to 28%, and a control group aged solely under a DC field. Our findings indicate that capacitors aged under the DC/AC‐superimposed field exhibited shorter lifespans and more significant capacitance loss than those aged under only the DC field. This difference in performance is primarily attributed to the distinct electrode loss behaviours observed under each ageing condition, which are key factors in the capacitors' capacitance decay. Moreover, the biaxially oriented polypropylene films in the DC‐aged samples showed more severe deterioration, characterised by more noticeable molecular chain scission and reduced breakdown strength, compared to those aged under the DC/AC superimposed field. This difference is partly due to the moderate temperature increase caused by harmonics, which benefits the aggregation structure, and partly to the reduced molecular structure damage from the AC field.
... A DC multi-port converter generally adopts a cascade structure with the same DC bus, and each port can operate independently and stably under this structure; however, a large electrolytic capacitor is usually required to support the DC bus voltage to realize energy decoupling between the converters [8]. Large electrolytic capacitors have a limited lifetime of 3000-5000 h, and their efficiency drops by 50% with a 10 • C increase in temperature, which reduces system usability and dependability [9]. Consequently, the large electrolytic capacitors are replaced by the small film capacitors owing to the advantages in operating time and stability of the small film capacitors. ...
... The addition of a control channel from the u bus to i bus is illustrated in Figure 15. Furthermore, the transfer of the ES converter output impedance changes from Equations (6) to (9). ...
The DC multi‐port converter's applications are increasing owing to its favourable features, including variable control mode, high power density, and bi‐directional power supply. On the other hand, the impedance interaction between each port of the electrolytic capacitor‐less DC multi‐port converter may generate an instability. To address the above mentioned problem, a method is proposed in this paper for reshaping the impedances of the energy storage converter by constructing a virtual impedance connected in parallel with the output impedance of the electrolytic capacitor‐less DC multi‐port converter. Furthermore, this paper introduces the stability criterion based on the unified impedance theory, which classifies a converter as either the bus current‐controlled converter or the bus voltage‐controlled converter. The proposed control approaches raise the magnitude of the output impedance of the electrolytic capacitor‐less DC multi‐port converter to satisfy the unified impedance theory criterion without modifying each port. The simulation results show that the proposed method is better than the traditional methods, and comprehensive experimental results are provided to validate the proposed methods.
... In addition to active components, it is crucial to evaluate the reliability of capacitors while conducting a reliability study for the entire system [22]. It is necessary to have knowledge about batteries, their state of charge, and their remaining useful life. ...
... In addition to active components, it is crucial to evaluate the reliability of capacitors while conducting a reliability study for the entire system [22]. It is necessary to have knowledge about ba eries, their state of charge, and their remaining useful life. ...
In electric or hybrid vehicles’ propulsion systems, Permanent Magnet-Assisted Synchronous Reluctance Machines represent a viable alternative to Permanent Magnet Synchronous Machines. Based on previous research work, the present paper proposes, designs, and optimizes two ferrite PMaSynRM topologies, analyzed against a reference machine (also PMaSynRM) with improved torque ripple content, based on similar specifications and dimensional constraints. Considering the trend of increasing the DC voltage level in electric and hybrid vehicles, the optimal topology is included in an analysis of the DC voltage level impact on the design and performances of PMSynRM.
... The decrease in capacitance of a capacitor indicates its progressive degradation. Depending on the type of capacitor, the end-of-life criterion is a different percentage of capacitance drop [6]. The effect of the degradation process is an increase in the ripple of the DC link voltage. ...
The article concerns the problem of capacitor diagnosis in a hybrid aircraft. Capacitors are one of the most commonly damaged components of electrical vehicle drive systems. The result of these failures is an increase in voltage ripple. Most known analytical methods are based on frequency spectrum analysis, which is time-consuming and computationally complex. The use of deep neural networks (DNNs) allows for the direct use of the measurement signal, which reduces the operating time of the overall diagnostic system. However, the problem with these networks is the long training process. Therefore, this article uses transfer learning (TL), which allows for the secondary use of previously learnt DNNs. To collect data to learn the network, a test bench with the ability to simulate a capacitor failure was constructed, and a model based on it was made in the MATLAB/Simulink environment. A convolutional neural network (CNN) structure was developed and trained by the TL method to estimate the capacitance of the capacitor based on signals from the Simulink-designed model. The proposed fault diagnostic method is characterised by a nearly 100% efficiency in determining capacitance, with an operating time of about 10 ms, regardless of load and supply voltage.
... In recent years, with the transformation of the power system and the needs of users, the topology structure of the PET has been continuously improved, including DC/AC, AC/AC, AC/DC, DC/DC, and other types. Among numerous PET topologies, the most common ones are CHB [12][13][14][15][16] and MMC [17][18][19][20][21] type PET. The CHB-type PET consists of several cascaded H-bridges and DC/DC transformers, with high output voltage and low energy loss. ...
This paper proposes a multi‐port medium‐frequency power electronic transformer (PET) topology for integrating photovoltaic (PV) generation with battery storage (BS). Firstly, this proposed PET provides multiple ports for renewable energy grid generation, so that it can achieve multi‐energy source management and energy complementary. Secondly, different from the conventional topology for renewable energy grid connected system, the proposed PET topology is safer and more reliable due to the separate connection of PV and BS through the voltage source converter to the primary winding of the PET. Finally, the PET only uses a single medium‐frequency transformer for voltage regulation and electrical isolation, so that it can avoid the use of DC capacitors in the traditional line/high‐frequency transformers, reduce the PET volume and its costs, as well as simplify the control strategy. The PET topology is introduced in detail and the simulation results verify the feasibility of the proposed topology.
... Therefore, a bulky aluminum electrolytic capacitor (AEC) is generally used [8] at the DC side to decouple the ripple power from the DC source. Since the life expectancy of the AEC is limited [9,10], it could be replaced by a more reliable film capacitor of equal capacitance, however it offers lower energy density and is costly as compared to the AEC [11]. Alternatively, active power decoupling (APD) methods [12][13][14] are suggested in the literature, where the bulky AEC is replaced by a switching network in conjunction with small passive elements to supply the ripple power. ...
Single-phase voltage source inverters typically employ a bulky and less reliable aluminum electrolytic capacitor at the DC side to eliminate the second-order (2\(\omega \)) ripple current from the DC source. Alternatively, attempts have been made to actively eliminate the second-order ripple current by modifying the converter topology and/or realizing the ripple current control loop. Recent reports have attempted to minimize the 2\(\omega \) ripple current by configuring the conventional H-bridge inverter as two differentially connected bidirectional buck converters. This arrangement called a differential buck inverter (DBI) leads to a common-mode current path, which is not present in the conventional H-bridge inverter. The common-mode path is used to eliminate the 2\(\omega \) ripple current. However, the analysis and control design of the ripple current control loop is not explored well in the existing literature. The present work analytically shows that the attempt to eliminate the 2\(\omega \) ripple current introduces additional ripple currents of nearby frequencies. Subsequently, an improved control scheme is developed to mitigate the ripple current from the DC side. Furthermore, the dynamics of the second-order generalized integrator, used to estimate ripple current from the DC side current, is included in the control design process, leading to a more stable and robust closed-loop system. All the analytical inferences and the efficacy of the proposed control are validated experimentally using a laboratory-developed 110 V, 50 Hz, 800 W DBI prototype.
... Furthermore, in addition to semiconductors, capacitors play considerably essential roles in improving the reliability of PECs which are responsible for 19% of failures [22]. In ref. [23], failure modes, failure mechanisms, and lifetime models of Aluminum Electrolytic Capacitors, Metallized Polypropylene Film Capacitors, and high capacitance Multi-Layer Ceramic Capacitors are discussed. Despite the aforementioned efforts, a comprehensive review paper to assess reliability strategies, encompassing both offline and online methods, is needed to be covered. ...
... The most commonly used capacitors for this purpose include aluminum electrolytic capacitors, multi-layer ceramic capacitors, and metalized polypropylene film capacitors. Furthermore, the main failure mechanisms for aluminum electrolytic capacitors are electrolyte vaporization and electromechanical reaction, for multi-layer ceramic capacitors it is moisture corrosion and dielectric loss, and for metalized polypropylene film capacitors it is insulation degradation and flex cracking [23], [147], [148], [149], [150]. More information about these types of capacitors can be found in [23]. ...
... Furthermore, the main failure mechanisms for aluminum electrolytic capacitors are electrolyte vaporization and electromechanical reaction, for multi-layer ceramic capacitors it is moisture corrosion and dielectric loss, and for metalized polypropylene film capacitors it is insulation degradation and flex cracking [23], [147], [148], [149], [150]. More information about these types of capacitors can be found in [23]. It should be noted that the lifetime of DC-link capacitors depends on the operating voltage and hotspot temperature, and a model for predicting the lifetime based on empirical data is provided in Equation (6). ...
Power electronics converters (PECs) are responsible for efficiently converting electrical energy between power generators, storage systems and power consumers/loads. The PECs are subjected to complicated power loading factors throughout their operations and, thus, are proven to have issues regarding lifetime. Therefore, according to the original equipment manufacturers and suppliers, the reliability of the PECs is a key priority in order to be widely used and accepted in the industries. In this context, this review article aims to provide a comprehensive overview of reliability assessment strategies and testing protocols for ensuring the lifetime requirements of PECs. In addition, the paper conducts a thorough investigation of various strategies that are employed to enhance reliability during the design and useful life phase, including the analysis of different types of failure mechanisms, identification of factors contributing to failures, and assessment of techniques for estimating and regulating junction temperatures to prolong the lifetime of the system under real-life operating conditions. Furthermore, the article highlights the challenges encountered in monitoring and predicting component degradation and outlines the crucial steps for conducting a functional safety analysis. Particular emphasis is provided on summarizing the different accelerated aging tests for power electronics converters used in automotive applications, as these tests have yet to be fully covered in previous literature. This study provides an overview and guidelines for understanding the reliability of PECs and identifying potential areas for future research. Finally, the paper concludes most of the ongoing research and innovations in this area and provides insights into the future trends and challenges in enhancing the reliability of power electronics converters
... Recent studies showed that faults in the power electronic converters account for a great share of the overall wind turbine systems faults, [7], [8], [9]. The DC link capacitors are regarded as one of the weakest parts in back-to-back power converters, [10], [11]. The DC link capacitor ripple current causes thermal stress, leading to a high percentage of the overall capacitor losses, [12]. ...
In this paper, the starting performance of a double-fed induction generator (DFIG) operating at super-synchronous speed is investigated when varying the values of the DC link capacitor. The starting transients, the settling time, and the harmonics of the stator and rotor currents and voltages are investigated as a function of the DC link capacitor Cd. Curve fitting is applied to derive mathematical equations (polynomial) relating the variation of the stator current THD with the value of the DC capacitor. Similarly, polynomials are deduced to relate the THD of the rotor current and rotor voltage with the value of the DC link capacitor. These polynomials help to design the DC link parameters that lead to minimum current and voltage harmonics of the grid-connected DFIG. The minimum THD values of the stator current, rotor current, and rotor voltage are presented. These results are repeated at different rotor speeds to deduce the optimum Cd value within a wide speed range. Also, the effect of Cd on the DC link current and voltage ripples is demonstrated at different speeds.
