Active Clamp Research Articles

Online monitoring of IGBT junction temperature based on Vce measurement

In this paper, an online junction temperature monitoring method based on the on-state voltage under high collector current density measurements for IGBT power modules is proposed. Unlike the conventional junction temperature monitoring method, the presented method can extract the junction temperature during operation without altering the modulation strategy or topology of the converter. The proposed method is verified by simulations and the JEDEC-51 standard recommended approach. To accurately extract the on-state voltage during operation, a measurement circuit that combines the advantages of both the active MOSFET clamp and the diode clamp is designed and tested. It has been shown to have good accuracy and a rapid response time. After the calibration results are obtained, the presented method is applied to a three-phase voltage source converter controlled by a closed-loop SVPWM modulation strategy.

Modeling and Reduction of Radiated EMI in a GaN IC-Based Active Clamp Flyback Adapter

This article first develops a radiated electromagnetic interference (EMI) model for a gallium nitride (GaN) integrated circuit (IC)-based active clamp flyback converter. Important capacitive couplings, which play a big role in the radiated EMI, are identified, extracted, and validated in the converter. The radiated EMI model is improved to characterize the impact of capacitive couplings. Based on the improved model, techniques to reduce capacitive couplings and the radiated EMI are proposed and experimentally validated.

Design Methodology of Quasi-Resonant Flyback Converter With a Divided Resonant Capacitor

The leakage inductance in flyback converters can induce high-voltage spikes in power switches as well as power losses. Although conventional resistor-capacitor-diode (RCD) snubbers and active clamp circuits can be used to suppress these voltage spikes, the clamping operation of RCD snubbers increases power consumption, while the active clamps require additional power switches. To address these issues, a quasi-resonant flyback converter featuring a divided resonant capacitor is proposed in this article, in order to suppress voltage spikes in power switches and improve the power conversion efficiency. The operational principle of a divided resonant capacitor is analyzed to obtain the design methodology of the divided resonant capacitor. Furthermore, the validity of the proposed design method is verified via experiments, using 15-W prototype quasi-resonant flyback converter. The results indicate that the proposed design effectively reduces voltage spikes and improves power conversion efficiency.

Digitally controlled GaN‐based MHz active clamp flyback converter with dynamic dead time optimisation for AC–DC adapter

The active clamp flyback (ACF) converter utilising gallium nitride (GaN) devices with high-switching frequency and high efficiency is impressive in system miniaturisation for AC–DC adapters. Owing to poor reverse conduction of GaN devices, the improper dead time between two switches can cause large power consumption in high frequency. This study proposes a dynamic dead time optimisation technique for GaNs ideal zero-voltage switching (ZVS) to address the issue. It adjusts the clamp switch on time to avoid large reverse conduction voltage stress on the main switch in different loads conditions. In addition, a new control scheme for clamp switch is introduced for enhancing efficiency in light to medium load. These techniques are experimentally verified on a 45 W (20 V/2.25 A) prototype of an ACF converter with a field-programmable gate array. The controller enables the system to operate at 1 MHz and dynamically modulates the dead-time under universal input and full load. With the light load ZVS control scheme, the system can achieve a maximum efficiency of 94.12 and 80.23% in the worst case. The prototyped converter can achieve power density (exclude case and controller) of 18 W/in3.

Control and monitoring of a Flyback DC-DC converter for photovoltaic applications using embedded IoT system

In this article, the authors present an Internet of Things (IoT) solution for controlling and monitoring a low power photovoltaic system (250 W). Power conditioning is performed by a DC-DC Flyback converter with active clamping. An ESP32 microcontroller is used to implement an output voltage control loop and to communicate, online and in real time, with an internet server. The effectiveness of voltage regulation is proven with experimental results and the authors present evidence that the IoT features work properly.

Model Predictive Control for a New Magnetic Linked Multilevel Inverter to Integrate Solar Photovoltaic Systems With the Power Grids

The multilevel inverters are becoming increasingly popular for use in the grid integration of wind and photovoltaic (PV) power plants due to their higher voltage handling capability and the better output power quality. There are several types of multilevel inverters that have been proposed in the literature; among them, the active neutral point clamp (ANPC) multilevel inverters have been drawing significant attention especially for solving the problems with other multilevel inverters. However, with the increase in the number of levels, the ANPC requires more electronic switches and flying capacitors, by which the complexity and the cost increase. In this article, an ANPC inverter with a reduced number of switches and flying capacitors is presented for the grid integration of the solar PV systems controlled using the model predictive control technique. This model predictive control technique uses a discrete-time model of the system to predict the future value of the active power and the reactive power for seven identified voltage vectors and selects the vector for the operation, which causes minimum cost function. The proposed power converter topology also effectively utilizes the dc bus voltage more when compared with the traditional ANPC converter. In the proposed inverter, a high-frequency transformer is used to eliminate the voltage balancing problems faced by the traditional ANPC inverters. The proposed magnetic linked power converter provides galvanic isolation, which is one of the most critical issues for traditional transformerless grid-connected PV systems. The proposed topology makes the control strategy simple and makes the power conversion system reliable for the PV power plants. The model predictive control-based power converter topology is simulated in MATLAB/Simulink environment and also validated in the laboratory test platform.

Soft-Switching Technology of Three-Phase Six-Switch PFC Rectifier

An active clamp, three-phase, six-switch power factor correction rectifier with a one-cycle controller is proposed, which can effectively suppress the reverse recovery of the reverse parallel diode of the bridge arm switch and reduce the reverse recovery loss. The main switches and auxiliary switch are both zero-voltage switches. It works in a fixed switching frequency and low power stress during the switching period. The specific working process and control circuit are analyzed in detail, and the model simulation is carried out. The experimental platform of a 2.5 KW prototype, with a complete test and verification of the soft switch technology proposed in this paper, was set up in the laboratory.

Sampled-Data Modeling for PCM and ZVS Controlled Critical Conduction Mode (CrCM) Active Clamp Flyback (ACF) Converter at Variable Switching Frequency

Critical conduction mode (CrCM) active clamp flyback (ACF) converter is regarded as a good candidate for low power adaptor applications. However, the most adopted control strategy of variable-frequency peak current mode (VF-PCM) and discrete zero voltage switch (ZVS) control makes it difficult to get the accurate small signal model. Therefore, by using sampled-data modeling method, this paper proposes an exact small signal model of CrCM ACF converter for the first time. In the modeling process, the influence of discrete-ZVS control is firstly considered. The conduction time of power switch is regarded as the control signal, which is different from constant-frequency converter. The total current close-loop transfer function is simplified by the linear combination of single VF-PCM and discrete-ZVS control model. After considering the sampling effect and the modulator gain from the derived sampled-data model respectively, the control-to-output transfer function of CrCM ACF converter is developed. The analytical results are analyzed by comparing with single VF-PCM and the widely used average model. Finally, to validate the accuracy of the proposed model, a 65W 20V output CrCM ACF converter is simulated and measured. The verification shown that the proposed sampled-data model is basically agreement with the simulation and experimental results.

Analysis and Optimal Design of High-Frequency and High-Efficiency Asymmetrical Half-Bridge Flyback Converters

The asymmetrical half-bridge (AHB) flyback converter is capable to achieve zero voltage switching and has lower voltage stress compared to the active clamp flyback converter. This topology gives much margin for components selection and transformer turns ratio design. It is well adapted to voltage step-down applications. However, the optimal design for AHB flyback converter taking current dip effect causing by components parasitic capacitances, and each component effect to power loss into consideration has never been explored. This article gives detailed operation and mathematical analyses of this effect. The optimal design procedure with the consideration of each circuit parameter is presented in this article. The transformer benefits low power loss from interleaving winding layout. A 56 W/inch3 1 MHz 65 W prototype with 100–250 V input is built to verify the feasibility of the converter. Experimental results show the peak efficiency 96.5% is achieved with 127 V input and the whole system efficiency under the entire input voltage range is above 93%.

Experimental validation of solar panel integrated modified three-port active clamp flyback converter fed micro-inverter

In this paper, a photovoltaic (PV) tied modified three-port active flyback converter (MTPACFC) operated three-phase micro-inverter is presented to provide enhanced voltage gain with fewer components. The proposed micro-inverter transfers the power generated on the 12 V PV power generation system to 400 V, AC grid. Generally, the DC-DC converter designed with an active clamp circuit provides improved power transfer capability to transfer the power from the PV array. The conventional active clamp flyback converters are designed to offer a limited boost factor for the input voltage. The recommended three-port altered flyback converter is intended to offer double boosting for the input voltage with extended performance. Besides, a synchronous reference frame theory with an artificial neural network based grid side controller is adapted to provide low total harmonic distortion at the point of common coupling. The outcomes of the simulated and test models are introduced to approve the boosting capacity and performance of the proposed MTPACFC.

Bidirectional Soft-Switching Converter With Reduced Current Ripple at Low-Voltage Side

Bidirectional dc–dc converters with storage devices and high-voltage conversion ratio are widely utilized in renewable energy systems in order to manage power flow between renewable sources, storage devices, and load. One of the most important parameters in these converters, which affects the lifetime of storage devices, is the pulsating current flowing through them. This article presents a bidirectional buck/boost converter that employs a coupled inductors technique to increase the voltage conversion ratio while the current in low-side voltage source is continuous. Furthermore, only an active clamp circuit, including a clamp capacitor and an auxiliary active switch, is utilized to create soft-switching conditions for the main switches and absorb the leakage inductance energy of coupled inductors for both high step-up/step-down operating states. In this converter, the soft-switching condition is provided for all switches without any extra element in the power flow direction. Also, all diodes turn off at the ZCS condition, which removes the reverse recovery problem. A low number of elements and fully soft-switching condition for all semiconductor devices have contributed to the converter efficiency. Theoretical analysis of the proposed converter in both operating states is presented in detail, and a 500-W prototype circuit is implemented to verify the validity of the theoretical analysis and converter performance.

Nanoscale Indentation of Plasma Membrane Establishes a Contractile Actomyosin Scaffold Through Selective Activation of the Amphiphysin-Rho1-Dia/DAAM and Rok Pathway

Nanoscale bending of plasma membrane increases cell adhesion, induces cell-signalling, triggers F-actin assembly and endocytosis in tissue-cultured cells. The underlying mechanisms are not very well understood. Here, we show that stretching the plasma membrane of somatic cyst cell around rigid spermatid heads generates a stable, tubular endomembrane scaffold supported by contractile actomyosin. The structure resembles an actin-basket covering the bundle of spermatid heads. Genetic analysis suggests that the actomyosin organisation is nucleated exclusively by the Formins, Diaphanous and DAAM, downstream of Rho1, recruited by the Bin-Amphyphysin-Rvs (BAR)-domain protein, Amphiphysin, around the spermatid heads. Actomyosin activity at the actin-basket gathers the spermatid heads into a compact bundle and resists the invasion of the somatic cell by the intruding spermatids. These observations revealed a new response mechanism of nanoscale bending of the plasma membrane, which generates a novel cell adhesion strategy through active clamping.

A Dynamic Resonant Period Control Technique for Fast and Zero Voltage Switching in GaN-Based Active Clamp Flyback Converters

Compared to Si FETs, when the main GaN FET is in full zero voltage switching condition, maximum switching loss reduction can be achieved. Therefore, in this article, an active clamp flyback converter with GaN devices that implements fast ZVS by using the proposed dynamic resonant period control (DRPC) technique can reduce large transformer leakage inductance energy loss on the active resonant circuit. As the loading changes, the DRPC technique can dynamically adjust the on -time in auxiliary switch to prevent large voltage stress on the components in the primary side. In full load condition, the leakage energy loss can be reduced, thereby transferring more energy to the secondary side with maximum efficiency up to 94%.

A Comparative Study of GaN HEMT and Si MOSFET-Based Active Clamp Forward Converters

Compared with conventional forward converters, active clamp forward (ACF) converters have many advantages, including lower voltage stress on the primary power devices, the ability to switch at zero voltage, reduced EMI and duty cycle operation above 50%. Thus, it has been the most popular solution for the low bus voltage applications, such as 48 V and 28 V. However, because of the poor performance of Si MOSFETs, the efficiency of active clamp forward converters is difficult to further improved. Focusing on the bus voltage of 28 V with 18~36 V voltage range application, the Gallium Nitride high electron-mobility transistors (GaN HEMT) with ultralow on-resistance, low parasitic capacitances, and no reverse recovery, is incorporated into active clamp forward converters for achieving higher efficiency and power density, in this paper. Meanwhile, the comparative analysis is performed for Si MOSFET and GaN HEMT. In order to demonstrate the feasibility and validity of the proposed solution and comparative analysis, two 18~36 V input, 120 W/12 V output, synchronous rectification prototype with different power devices are built and compared in the lab. The experimental results show the GaN version can achieve the efficiency of 95.45%, which is around 1% higher than its counterpart under the whole load condition and the same power density of 2.2 W/cm3.

Soft-Switching High Step-Up/Down Converter Using Coupled Inductors With Minimum Number of Components

This article presents a soft-switching buck-boost converter with high step-up/down conversion ratio. The popular coupled inductors method is employed to achieve high step-up/down gain conversion. Moreover, a simple auxiliary circuit, including a small capacitor, active switch, and an extra winding on the coupled inductors, is utilized to provide soft-switching condition for the main switches in both operating states. This simple auxiliary circuit is a proper substitute for two essential active clamp circuits required in bidirectional converters with coupled inductors. Also, the added auxiliary winding is employed in the power flow path to increase the step-up/down voltage gain. All switches have zero current switching (ZCS) turn-on and zero voltage ZCS (ZVZCS) turn-off performance, which eliminates the reverse recovery problem of switches body diodes and improves converter efficiency. A 300-W prototype converter with 48-380 V conversion ratio is realized to confirm the validity of theoretical analysis and the operation of the proposed converter.

Comparision of Voltage Stress Across the MOSFET Switch of a Flyback Converter with Various Snubbers

A Flyback converter is a simple switch-mode power supply that can be used to generate a DC output from either an AC or DC input. The converter switch is the most critical part of any converter. The voltage stress across the switch is a major issue as the high voltage spikes occur due to interaction between its output capacitance and the leakage inductance of the transformer. These spikes can be reduced with various snubbers like conventional tertiary winding, Resistor Capacitor and Diode(RCD) snubber, energy regenerative snubber and an active clamp snubber. This paper aims to analyze and compare the voltage stress across the MOSFET switch of Flyback converter with various snubber circuits.

A novel regenerative snubber circuit for flyback topology converters

Switch mode power suppliers based on isolated flyback topology have voltage stresses on semiconductor switches caused by transformer leakage inductance. Those voltage stresses have to be mitigated by implementing active or passive clamp preferably with partial leakage energy recovery. In this paper a new integrated semi-active regenerative (lossless) snubber is proposed. The proposed snubber topology is featured by the snubber inductor integrated into the main transformer thus decreasing component count and saving the PCB space. Partial coupling of snubber inductor with a secondary side makes it possible to recover part of the transformer leakage energy directly to the secondary side with potential to increase snubber efficiency. The operation of the proposed snubber is analyzed and simulation results are presented. Interesting is that with the proposed snubber various side effects can be reached like reduction of RMS current in secondary side, ZCS and ZVS modes for secondary side rectifier and primary main switch along with achieved primary goal – voltage stress limitation and transformer leakage energy recovery.

A Dual Active Clamp DC–DC Converter With High Voltage Gain

In this article, a novel dual active clamp converter with high voltage gain is proposed for dc-dc applications. The active clamps' switches turn on and off under zero-current switching (ZCS). In addition, the main switch turns on under ZCS condition, as well. Therefore, switching losses are significantly reduced. The converter is also capable of operating under quasi-resonance (QR) mode. In this mode, switching losses are reduced further by lowering the voltage and current, at which the main switch turns off. In comparison with the conventional interleaved converter, the voltage gain of the proposed converter is almost the same, but the number of semiconductors and switching loss are significantly reduced. The switching frequency of the active clamps' switches is half of the main switching frequency. The operation principles of the proposed converter are studied in both pulsewidth modulation and QR modes, and the advantages are investigated. A 200-W prototype is implemented to validate the desired functionality of the converter, and experimental results are compared in both modes.

Performance-Based Active Wafer Clamp Design for Wafer Heating Effects in EUV Lithography

To improve overlay and focus errors in lithographic applications, an active wafer clamp (AWC) concept is proposed. Using this concept, mechanical actuators deform the wafer to compensate thermally induced deformations. In [1] a localized feedforward (FF) control algorithm for the AWC concept was introduced. In this paper we aim to improve this algorithm and discuss practical implications for the design of an AWC concept, motivated by the optimal performance that can be achieved using the FF control scheme. This leads to a design, where the actuators are placed below the clamping electrode, and 3-degree-of-freedom (DOF) actuators can be reduced to 2-DOF actuators with negligible performance loss. Considering the fact that the AWC concept contains tens of thousands of actuators, this leads to a significant reduction. Finally, other methods are presented to further reduce the computational complexity to control the AWC.

Trends and Challenges in Grid-Tied Inverters for Photovoltaic Applications

Grid-Tied inverter has gained the attention of many researchers and power generation industry due to its capability of integrating distributed power generation systems using renewable energy resources with the existing centralized power generation system. Yet the inclusion of a transformer in the Photovoltaic (PV) inverter makes it bulkier, heavier and more expensive. A primary solution to the aforementioned problems is the transformerless PV Grid-Tied inverter. This paper presents a review of different transformerless, single-phase Grid-Tied inverter topologies. The objective of this paper is to study parameters such as leakage current, common-mode voltage, total harmonic distortion, and the efficiency of transformerless Grid-Tied inverters. The paper also provides a discussion on existing Grid-Tied inverter topologies, such as H5, oH5, Novel H5, H5-D, FBDC, H6D2, Hybrid H6, High-efficiency MOSFET H6, Improved H6, 3L H6, H6-A, B, High-Efficiency H6, H6-N, Improved H6, H6-active clamping, Active clamped snubber based H6, Heric, oHeric, Enhanced Heric, Heric-with mid-DC-link, Active clamping, PN-NPC, Improved FBNPC, T-Type 3L, ANPC, HBNPC, NIFB-NPCI, VNIIFBC, M-NPC, Virtual DC bus based inverter, Active Virtual Ground, Type I, Type II, Type III Common Ground, Flying Capacitor and Multilevel Common Ground. Though it is found that many topologies available in the literature, other new topologies can be proposed to improve the performance of the inverter. Furthermore, it is also noted that the performance analysis of the inverter must be carried out in the presence of junction capacitance and shoot-through problem so that new strategies can be introduced in the existing typologies to address these issues.