Bulky Electrolytic Capacitors Research Articles

A Novel Bidirectional T-Type Multilevel Inverter for Electric Vehicle Applications

This paper introduces a new configuration of bidirectional multilevel converter in electric vehicle (EV) applications. It has multilevel dc–dc converter with a dc link capacitor voltage balance feature. The multilevel dc–dc converter operates in a bidirectional manner, which is a fundamental requirement in EVs. Compared to the conventional configurations, the proposed one only implements two extra power switches and a capacitor to balance the voltage of the T-type multilevel inverter (MLI) capacitor over a complete drive cycle or at fault conditions. Therefore, no extra isolated sensor, control loops, and/or special switching pattern are required. Moreover, the proposed configuration due to the high-frequency cycle-by-cycle voltage balance between ${C_N}$ and ${C_P}$ , the bulky electrolytic capacitors used in T-type MLI, are replaced with more reliable longer life film capacitors. This will result in a size and weight reduction of the converter by 20%. This allows more real estate for the EV battery in the chassis’ space envelope to increase its capacity. The proposed configuration is tested and validated using a matlab /Simulink simulation model. A laboratory prototype of 1 kW is built to provide the proof of concept results as well.

On‐Chip MXene Microsupercapacitors for AC‐Line Filtering Applications

AbstractMicrosupercapacitors (MSCs) with high energy densities offer viable miniaturized alternatives to bulky electrolytic capacitors if the former can respond at the kilo Hertz (kHz) or higher frequencies. Moreover, MSCs fabricated on a chip can be integrated into thin‐film electronics in a compatible manner, serving the function of ripple filtering units or harvesters of energy from high‐frequency sources. In this work, wafer‐scale fabrication is demonstrated of MXene microsupercapacitors with controlled flake sizes and engineered device designs to achieve excellent frequency filtering performance. Specifically, the devices (100 nm thick electrodes and 10 µm interspace) deliver high volumetric capacitance (30 F cm−3 at 120 Hz), high rate capability (300 V s−1), and a very short relaxation time constant (τ0 = 0.45 ms), surpassing conventional electrolytic capacitors (τ0 = 0.8 ms). As a result, the devices are capable of filtering 120 Hz ripples produced by AC line power at a frequency of 60 Hz. This study opens new avenues for exploring miniaturized MXene MSCs as replacements for bulky electrolytic capacitors.

SVPWM Method for Multilevel Indirect Matrix Converter with Eliminate Common Mode Voltage

The multilevel indirect matrix converter (IMC) is a merit of power converter for feeding a three-phase load from three-phase power supply because it has several attractive features such as: Sinusoidal input/output currents, bidirectional power flow, long lifetime due to the absence of bulky electrolytic capacitors. As compared to the conventional IMC, the multilevel IMC provides high output performance by increasing the level of output voltage. In this paper, the novel approach topology of multilevel IMC by using the combination of the cascaded rectifier and the three-level T-Type inverter is introduced. Furthermore, the new space vector pulse width modulation (SVPWM) method for the presented multilevel IMC that eliminate the common-mode voltage is proposed in this paper. The simulation study is carried out in PSIM software to verify the proposed modulation method. Then, an experimental system is built using a three-phase RL load, a multilevel IMC, a DSP controller board and other elements to verify the effectiveness of the proposed modulation method. Some simulation and experimental results are illustrated to confirm the theory analysis.

Single-Stage Isolated Electrolytic Capacitor-Less EV Onboard Charger With Power Decoupling

In this paper, a new single-stage single-phase isolated AC-DC converter derived from a differential boost AC-DC converter is proposed. This converter eliminates the need to use the bulky electrolytic capacitor from the system and at the same time provides DC charging by employing the AC Power Decoupling waveform control method, effectively addressing the power density and reliability related issues commonly associated with the bulky electrolytic capacitor. As half of the switches of this converter act as synchronous rectifier during half grid cycle they are inherently ZVS Turned On while the remaining switches achieve ZVS Turn On as they act as synchronous rectifier during other half grid cycle. However, all diodes at the secondary side achieve ZCS Turn Off during the entire line cycle. A conventional controller is implemented for output voltage regulation and PFC control whereas a power decoupling controller is added to compensate second harmonic ripple power. Besides, an interleaving technique is applied to provide high-frequency links for transformers' connection while at the same time increasing the power range and effectively reducing the size of the input filter. Finally, the operating principle of the converter is validated through simulation, and the experimental results are provided.

A Single-Stage Soft-Switching High-Frequency AC-Link PV Inverter: Design, Analysis, and Evaluation of Si-Based and SiC-Based Prototypes

This paper proposes a high-power-density and reliable inverter topology, which transfers the maximum power of a PV array to the load in one power conversion stage. The single-stage power conversion, along with the soft-switching capability of the proposed three-phase PV inverter promises high efficiency at all operating points. Instead of a capacitive dc link that decouples the dc–dc converter and the voltage source inverter in traditional two-stage PV inverters, a high-frequency capacitive ac link is employed in the proposed inverter, which enables exploiting a very small film capacitor, rather than a bulky electrolytic capacitor, for transferring power. Eliminating electrolytic capacitors prolongs the lifetime of this inverter. Considering the long lifetime of PV modules, this feature is of high importance in PV applications. The high-frequency ac link also allows using high-frequency transformers for providing galvanic isolation. Therefore, this inverter is expected to have a very high power density. This paper presents principles of the operation and control, design, and analysis of this inverter, and verifies the performance of the inverter through two prototypes: a 2-kW Si-based prototype and a 2-kW SiC-based prototype operating at different switching frequencies.

A Bridgeless Electrolytic Capacitor-Free LED Driver Based on Series Resonant Converter With Constant Frequency Control

High-brightness light-emitting diode (LED) is next generation of green lighting. However, the bulky electrolytic capacitor is required to compensate the difference of pulsating power, thereby restricting the lifetime. Meanwhile, the existing drivers based on pulse frequency modulation (PFM) is bound to arouse heavy electromagnetic interference. In this paper, the series resonant converter based LED drive is proposed to overcome the shortcomings of electrolytic capacitor and PFM control. The proposed method is to attenuate the low frequency ripples delivered from the power factor correction (PFC) to LEDs; therefore, the capacitance is reduced for energy storage of offline LED drivers. On account of the adoption of the switching controlled capacitor (SCC), the constant frequency control is achieved by the regulations of the equivalent capacitance. Half-bridge switches are shared by the bridgeless PFC and the resonant unit, therefore, single-stage LED drive is realized with high efficiency. In addition, SCC is simultaneously shared for the upper and lower half-bridge to reduce the cost and improve the power density. Operating principle, design considerations, and performance comparisons are examined in detail. Finally, all the superior performances of proposed LED driver are verified by simulation and experimental prototypes with two-channel LEDs, and rated output power of 80 W.

Circuit-integratable high-frequency micro supercapacitors with filter/oscillator demonstrations

Micro supercapacitor (MSC) featured by high capacitance density, has great potential for replacing bulky electrolytic capacitors in circuits to make electronics of miniaturization, yet suffers from sharp capacitance drop under alternating current. Here, we report a circuit-integratable high-frequency MSC with hybrid architecture electrode, in which 2D pseudocapacitive MXene served as the active material provides large capacitance and multi-walled carbon nanotube applied as interlayer support offers fast ion transport paths. Such design brings the device an excellent frequency response and a capacitance density much higher than commercial tantalum capacitors at 120 Hz. A novel transfer-free filtration technology greatly eliminates the equivalent series resistance and the consequent thermal loss, and makes the MSC a more circuit-integratable planar geometry. Moreover, such high-frequency MSC is applied in a low-pass filtering circuit and a relaxation oscillator circuit, displaying advantages in function, size and intergratability compared with electrolytic capacitors.

Active power decoupling and controlling for single‐phase FACTS device

Single-phase FACTS device has a bulky and short-life electrolytic capacitor to absorb the ripple pulsating at twice of the line frequency in DC side, resulting in lower power density. This paper introduced a structure of three-phase bridge which added an additional leg connected to an AC capacitor based on single-phase H-bridge. The 2-ripple energy of the electrolytic capacitor in single-phase H-bridge could be transformed to the film capacitor of the AC side in three-phase H bridge. The size of single-phase FACTS is reduced by ten times compared to the single-phase H-bridge. A simple control strategy had been studied, through two kinds of controllers: the digital quais-PR controller had been used to control gird current and AC capacitor voltage and current; the two cosine controller had been used to eliminate the rest of two-ripple harmonic in the DC side, there was no controller to maintain DC voltage. The experiments verified the feasibility of the control strategy.

Compact and low loss electrochemical capacitors using a graphite / carbon nanotube hybrid material for miniaturized systems

With the establishment of the internet of things (IoT) and the rapid development of advanced microsystems, there is a growing demand to develop electrochemical capacitors (ECs) to replace bulky electrolytic capacitors on circuit boards for AC line filtering, and as a storage unit in energy autonomous systems. For this purpose, ECs must be capable of handling sufficiently high signal frequencies, display minimum energy loss through self-discharge and leakage current as well as maintaining an adequate capacitance. Here, we demonstrate ECs based on mechanically flexible, covalently bonded graphite/vertically aligned carbon nanotubes (graphite/VACNTs) hybrid materials. The ECs employing a KOH electrolyte exhibit a phase angle of −84.8°, an areal capacitance of 1.38 mF cm−2 and a volumetric capacitance (device level) of 345 mF cm−3 at 120 Hz, which is among the highest values for carbon based high frequency ECs. Additionally, the performance as a storage EC for miniaturized systems is evaluated. We demonstrate capacitive charging/discharging at μA current with a gel electrolyte, and sub-μA leakage current reached within 50 s, and 100 nA level equilibrium leakage within 100 s at 2.0 V floating with an ionic liquid electrolyte.

A Single-Phase Inverter/Rectifier Topology With Suppressed Double-Frequency Ripple

This paper introduces a new bidirectional single-phase inverter topology. The proposed topology has three ports: a dc port, an ac port, and a ripple port. The ac and dc ports are bidirectional to support rectifier or inverter operation. A small inductor, which is of alternating current, exchanges power between different ports of the single-phase system. The proposed topology is capable of accomplishing voltage step-up or step-down, suppressing the ripple power, and performing inversion or rectification operation in one stage of power conversion. The proposed configuration offers an active decoupling function, which not only eliminates the double-frequency ripple power at the dc port but also achieves minimum capacitance requirements to minimize the size of the decoupling capacitor. This facilitates the use of a very small thin-film capacitor, which offers a much longer life-cycle and higher reliability compared with a bulky electrolytic capacitor. A control approach is also developed to regulate the dc-port and ac-port currents and manage the ripple power through proper distribution of power between each port. Moreover, a very small capacitor can be placed in parallel with the inductor to reinforce the proposed configuration with soft-switching operation, which enhances the overall efficiency and minimizes the voltage stress over the semiconductor devices. This converter is capable of accommodating an arbitrary number of dc or single-phase ac sources and/or loads configuring a multiple-input multiple-output inverter without introducing any additional passive elements or sacrificing the performance of the inverter. The primary focus of this paper is dc-to-ac conversion mode of operation, in spite of the fact that it can easily be configured to serve as a rectifier. Experimental and simulation results are presented to validate the operation of the proposed topology and its control strategy.

Control Method for the Sheppard–Taylor PFC Rectifier to Reduce Capacitance Requirements

Sheppard–Taylor power factor correction (ST-PFC) rectifier could obtain a high power factor due to its capability of overcoming the control detuning issue. However, it needs a bulky electrolytic capacitor at the load side to buffer the double-frequency ripple power (DFRP), which reduces the reliability and power density significantly. This paper proposes a control method to divert the DFRP to the small energy transfer capacitor. Consequently, the bulky electrolytic capacitor is replaced with a small film capacitor. The proposed method is carried out by introducing the freewheel state (one switch is turned on and the other is turned off ) into the control. So no extra hardware is added, which makes the proposed method cost-effective. A low electromagnetic interference emission is also achieved due to the continuous input–output currents. In addition, the proposed method can be extended to other topologies easily. This paper first gives the detailed analysis of the proposed control method, and then introduces the controller design. The selection of the passive components is also briefly discussed. Finally, the simulation and experimental results verify the effectiveness of the proposed control method.

Reducing the dc-Link Capacitance: A Bridgeless PFC Boost Rectifier That Reduces the Second-Order Power Ripple at the dc Output

This Article Proposes a Novel single-phase bridgeles power factor correction (PFC) boost rectifier with a small dc-link capacitor that can reduce the second-order power ripple at the dc output side. An auxiliary circuit was added to decouple the active power at the dc link, which forces the voltage ripple to divert to the auxiliary capacitor. Therefore, the dc-link capacitance can be reduced significantly. As a result, the bulky electrolytic capacitor can be replaced with a small film capacitor. The experimental results verified the validation of the proposed method.

A Robust DC-Split-Capacitor Power Decoupling Scheme for Single-Phase Converter

Instead of bulky electrolytic capacitors, active power decoupling circuit can be introduced to a single-phase converter for diverting second harmonic ripple away from its dc source or load. One possible circuit consists of a half-bridge and two capacitors in series for forming a dc-split capacitor, instead of the usual single dc-link capacitor bank. Methods for regulating this power decoupler have earlier been developed, but almost always with equal capacitances assumed for forming the dc-split capacitor, even though it is not realistic in practice. The assumption should, hence, be evaluated more thoroughly, especially when it is shown in the paper that even a slight mismatch can render the power decoupling scheme ineffective and the IEEE 1547 standard to be breached. A more robust compensation scheme is, thus, needed for the dc-split capacitor circuit, as proposed and tested experimentally in the paper.

Edge-Oriented Graphene on Carbon Nanofiber for High-Frequency Supercapacitors

High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3D edge-oriented graphene (EOG) was grown encircling carbon nanofiber (CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at − 45° phase angle was found to be as high as 22 and 8.5 kHz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 mF cm−2 for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promising potential of this technology for compact power supply design and other applications.

A Control Method for Bridgeless Cuk/Sepic PFC Rectifier to Achieve Power Decoupling

Bulky electrolytic capacitor is usually needed in bridgeless power factor correction rectifiers to buffer the double-frequency ripple power (DFRP). However, it reduces the system reliability and power density significantly. This letter proposed a control method to divert DFRP to the small energy transfer capacitor. Then, the bulky electrolytic capacitor can be replaced with a small film capacitor. The proposed method is realized by making the best of the existing switching states. Therefore, it needs no extra switches or energy storage components, which are usually required in other active power decoupling methods. The operating principle is explained, and a closed-loop control strategy is proposed. Finally, the effectiveness is verified by experimental results.

Coupled-Inductor-Based High-Step-Down-Ratio Converter with Output Current Ripple Reduction

Even though the coupled-inductor-based high-step-down-ratio converters can achieve a higher step-down voltage gain than the traditional buck converter, their output current suffer from a high output current ripple, causing a high output voltage ripple. Therefore, a bulky electrolytic output capacitor is usually used to suppress the output voltage ripple. Moreover, the longevity of the output electrolytic capacitor is highly dependent on the output current ripple. In [6–8], a passive current ripple cancellation circuit was applied to the DC–DC converters to reduce the output current ripple. However, these literatures did not mention and analyze the situations for coupled-inductor converters. Moreover, the same concept, including analysis and design, cannot be directly applied to the coupled-inductor-based converters. Therefore, in this paper, the analysis, design, and experimental results of the current ripple cancellation circuit applied to the coupled-inductor-based high-step-down-ratio converter are given to verify the effectiveness.

Non‐pulsating input and output current Cúk, SEPIC, Zeta and Forward converters for high‐voltage step‐up applications

Four families of non-isolated single-switch Cuk, SEPIC, Zeta and Forward converters are derived. They incorporate coupled-inductor, voltage-doubler and voltage clamping circuits to accomplish a high DC voltage step-up at high-efficiency levels. Besides Cuk and SEPIC, Zeta and Forward can also have the advantage of operating with continuous input and output currents, which provide accurate tracking of the maximum power point of photovoltaic modules and a reduction in the use of DC-link bulky electrolytic capacitors.

An AC Input Switching-Converter-Free LED Driver With Low-Frequency-Flicker Reduction

This paper presents a novel switching-converter-free ac–dc light-emitting diode (LED) driver with low-frequency-flicker reduction for general lighting applications. The proposed driving solution can minimize the system size as it enables the monolithic integration of the controller and power transistors while both the bulky off-chip electrolytic capacitors and magnetics are eliminated. Moreover, the driver can effectively reduce the harmful optical flicker at the double-line-frequency by employing a novel quasi-constant power control scheme while maintaining high efficiency and a good power factor (PF). The proposed driver is implemented with a single controller integrated circuit chip, which includes the controller and high-voltage power transistors, and the off-chip diode bridge and valley-fill circuit. The chip is fabricated with a 0.35- $\mu \text{m}$ 120-V high-voltage CMOS process and occupies 1.85 mm2. The driver can provide up to 7.8-W power to the LED and achieves 87.6% peak efficiency and an over 0.925 PF with only 17.3% flicker from a 110-Vac 60-Hz input.

Beijing Converters: Bridge Converters With a Capacitor Added to Reduce Leakage Currents, DC-Bus Voltage Ripples, and Total Capacitance Required

Isolation transformers and bulky electrolytic capacitors are often used in power electronic converters to reduce leakage currents and voltage ripples but this leads to low power density and reduced reliability. In this paper, an auxiliary capacitor is added to the widely used conventional full-bridge converter to provide a path for, and hence significantly reduce, the leakage current. The operation of the full-bridge converter is split into the operation of a half-bridge converter and a dc–dc converter so that the ripple energy can be diverted from the dc-bus capacitor to the auxiliary capacitor. Hence, the dc-bus capacitor can be significantly reduced while maintaining very low voltage ripples on the dc bus because it is only required to filter out switching ripples. The auxiliary capacitor is designed to allow high voltage ripples because its voltage is not supplied to any load. Accordingly, the auxiliary capacitor can also be very small as well. As a result, the total required capacitance becomes very small. The reduction ratio of the total capacitance is significant, which makes it cost-effective to use film capacitors instead of electrolytic capacitors. The proposed converters can be also operated as an inverter without any restriction on power factor because the adopted four switches are all bidirectional in terms of power flow. Experimental results for both rectification and inversion modes are presented to demonstrate the performance of the proposed converter in reducing the ripples, the leakage currents, and the total capacitance needed, with comparison to the conventional bridge converter without the auxiliary capacitor.

A High-Efficiency Quasi-Single-Stage Bridgeless Electrolytic Capacitor-Free High-Power AC–DC Driver for Supplying Multiple LED Strings in Parallel

In order to design a high-efficiency, cost-effective, high-power driver for supplying multiple light-emitting diode (LED) strings in parallel, a novel single-stage bridgeless, soft-switched integrated AC-DC converter is proposed. The proposed converter can be derived by integrating the totem-pole bridgeless boost power factor correction (PFC) circuit and half-bridge LLC resonant converter. Therefore, the number of semiconductors in the line-current path can be significantly minimized, and the power losses in the secondary rectifier diodes and the primary switches can be dramatically reduced. Moreover, the twin-bus concept can be adopted to achieve the quasi-single-stage power conversion of the total LED driver with multiple LED strings load. In addition, this circuit allows removing the bulky electrolytic capacitors with short lifetime by increasing the bus voltage ripple, and thus, the long lifetime is another advantage of the proposed LED driver. The detailed operation principles and design considerations for the proposed converter are analyzed and discussed. The feature of the proposed solution was demonstrated using a 100-W hardware prototype with six LED strings. The experimental results showed the converter achieves full-range ZVS for primary switches and the efficiency of 94.5% under the 120 V input voltage.