Switched-mode Power Converters Research Articles

Very High Frequency PWM Buck Converters Using Monolithic GaN Half-Bridge Power Stages With Integrated Gate Drivers

Integration is a key step in utilizing advances in GaN technologies and enabling efficient switched-mode power conversion at very high frequencies (VHF). This paper addresses design and implementation of monolithic GaN half-bridge power stages with integrated gate drivers optimized for pulsewidth-modulated (PWM) dc-dc converters operating at 100 MHz switching frequency. Three gate-driver circuit topologies are considered for integration with half-bridge power stages in a 0.15-μm depletion-mode GaN-on-SiC process: an active pull-up driver, a bootstrapped driver, and a novel modified active pull-up driver. An analytical loss model is developed and used to optimize the monolithic GaN chips, which are then used to construct 20 V, 5 W, 100 MHz synchronous buck converter prototypes. With the bootstrapped and the modified pull-up gate-driver circuits, power stage efficiencies above 91% and total efficiencies close to 88% are demonstrated. The modified active pull-up driver, which offers 80% reduction in the driver area, is found to be the best-performing approach in the depletion-mode GaN process. These results demonstrate feasibility of high-efficiency VHF PWM dc-dc converters based on high levels of integration in GaN processes.

Aging Detection Capability for Switch-Mode Power Converters

The detection of degradations and resulting failures in electronic components/systems is of paramount importance for complex industrial applications including nuclear power reactors, aerospace, automotive, and space applications. There is an increasing acceptance of the importance of detection of failures and degradations in electronic components and of the prospect of system-level health monitoring to make a key contribution to detecting and predicting any impending failures. This paper describes a parametric system identification-based health-monitoring method for detecting aging degradations of passive components in switch-mode power converters (SMPCs). A nonparametric system response is identified by perturbing the system with an optimized multitone sinusoidal signal of the order of mVs. The parametric system model is estimated from nonparametric system response using recursive weighted least-square (WLS) algorithm. Finally, the power-stage component values, including their parasitics, are extracted from numerator and denominator coefficients based on the assumed Laplace system model. These extracted component values provide direct diagnostic information of any degradation or anomalies in the components and the system. A proof of concept is initially verified on a simple point-of-load (POL) converter but the same methodology can be applied to other topologies of SMPC.

An All-Digital Fast Tracking Switching Converter with a Programmable Order Loop Controller for Envelope Tracking RF Power Amplifiers.

This paper presents a step down, switched mode power converter for use in multi-standard envelope tracking radio frequency power amplifiers (RFPA). The converter is based on a programmable order sigma delta modulator that can be configured to operate with either 1st, 2nd, 3rd or 4th order loop filters, eliminating the need for a bulky passive output filter. Output ripple, sideband noise and spectral emission requirements of different wireless standards can be met by configuring the modulator's filter order and converter's sampling frequency. The proposed converter is entirely digital and is implemented in 14nm bulk CMOS process for post layout verification. For an input voltage of 3.3V, the converter's output can be regulated to any voltage level from 0.5V to 2.5V, at a nominal switching frequency of 150MHz. It achieves a maximum efficiency of 94% at 1.5 W output power.

FPGA (Field Programmable Gate Array) controlled solar based zero voltage and zero current switching DC–DC converter for battery storage applications

The objective of the paper is to develop a solar based soft switching isolated DC–DC converter for battery charging applications. The use of conventional boost converter is likely to decrease the efficiency because of hard switching, which generates loss during the switch on/off. But soft switching technique informs well with zero-current switching by the resonant inductor at turn-on, and zero-voltage switching by the resonant capacitor at turn-off. The major drawback of switched mode power converter operation is to produce EMI due to large dv/dt and di/dt during the time of switch mode operation. Therefore, to realize high switching frequencies in converters, the switching losses and EMI emission are reduced if each controlled switch in the converter is turn-on or turn-off only when current passing through and or voltage across the switch is zero. The FPGA (Field Programmable Gate Array) controlled DC–DC converter is used to provide zero voltage and zero current switching of all the main power devices. In this paper, the gate pulses are generated from FPGA (Field Programmable Gate Array) controller. This paper also describes the main operational modes of the converter as well as its simulation and Hardware results.

Simplified ferrite core loss separation model for switched mode power converter

Without depending on numerous material parameters or any special testing equipment, this study proposes a simplified and generalised ferrite core loss separation model for power magnetic components in switched mode power converter. The components of hysteresis loss and eddy current loss are treated as two packages which can be directly calculated from the loss data supplied by manufacturers. The value of resistivity changes with the frequency and the temperature, and the proposed separation method can alleviate the effect of resistivity on calculating the eddy current component. Based on the different isolating layers in ferrite materials, a correction coefficient is proposed to define the effect of cross-sectional area has on the eddy current loss. The experiments with both sinusoidal excitation and square excitation verify the theoretical results. The proposed method shows a quantitatively theoretical tool for predicting the power loss in ferrite core.

Merged Flyback–SC-Based Output Stage for Versatile Portable Transcutaneous Electrical Stimulators

This paper introduces a highly flexible multichannel output stage for battery-powered portable electric stimulators (ESs), based on novel power converter architecture. Compared with other solutions, the presented output stage for transcutaneous (surface) stimulations increases the number of applicable therapies, improves the battery operating time through reduced power consumption, and potentially results in more comfortable and shorter healing therapies. The new hybrid switch-mode power converter is a combination of flyback and switched-capacitor (SC) topologies. The flyback steps up the battery voltage and provides galvanic isolation. The following power-efficient SC stage replaces lossy linear current sources (CSs) of conventional solutions and produces pulses with a much higher slew rate, reducing the pulse energy needed to cause the stimulus. The SC also inherently produces pulses with zero-net charge, eliminating bulky blocking capacitors and/or dedicated discharging circuits. The regulation of the amplitudes of the pulses is performed with a new digital voltage-programmed current mode controller, forcing the output of the SC stage to behave as a CS. The flexible digital controller allows for creation of various types of pulses and also features several levels of patient protection. An experimental prototype of the output stage has undergone proof of principle tests with able-bodied individuals. The results show that the new output stage produces pulses with a 1-mA/ns slew rate, about two orders of magnitude higher than the other known solutions. The trials show that the faster slew rate pulses generate the same muscle contraction with 34% lower amplitudes, reducing energy consumption by 55%, allowing longer battery life of portable ES applications.

An Automatic Switched-Capacitor Cell Balancing Circuit for Series-Connected Battery Strings

In this paper, a novel voltage equalizer is developed for series battery strings based on the two-phase switched capacitor technique. Different from the conventional voltage equalizers which are developed by switched-mode power converters, bulky magnetic components and complex monitoring and control system are avoided in the proposed system. Just a pair of complementary pulse signals with constant switching frequency and fixed duty ratio are required to control all of switches employed in the proposed voltage equalizer, and charge transfers from the higher voltage battery cells to lower voltage ones automatically. The circuit configuration and operation principle are provided in this paper. The model of the proposed voltage equalizer is also derived. Comparison with other works indicates that the proposed method is superior to the conventional switched-capacitor (SC) voltage equalizer for the high stack of series battery strings. Experimental results demonstrate that the proposed voltage equalization system is capable of excellent voltage balancing performance with a simple control method.

Storage-Less and Converter-Less Photovoltaic Energy Harvesting With Maximum Power Point Tracking for Internet of Things

Energy harvesting from natural environment gives range of benefits for the Internet of things. Scavenging energy from photovoltaic (PV) cells is one of the most practical solutions in terms of power density among existing energy harvesting sources. PV power systems mandate the maximum power point tracking (MPPT) to scavenge the maximum possible solar energy. In general, a switching-mode power converter, an MPPT charger, controls the charging current to the energy storage element (a battery or equivalent), and the energy storage element provides power to the load device. The mismatch between the maximum power point (MPP) current and the load current is managed by the energy storage element. However, such architecture causes significant energy loss (typically over 20%) and a significant weight/volume and a high cost due to the cascaded power converters and the energy storage element. This paper pioneers a converter-less PV power system with the MPPT that directly supplies power to the load without the power converters or the energy storage element. The proposed system uses a nonvolatile microprocessor to enable an extremely fine-grain dynamic power management in a few hundred microseconds. This makes it possible to match the load current with the MPP current. We present detailed modeling, simulation, and optimization of the proposed energy harvesting system including the radio frequency transceiver. Experiments show that the proposed setup achieves an 87.1% of overall system efficiency during a day, 30.6% higher than the conventional MPPT methods in actual measurements, and thus a significantly higher duty cycle under a weak solar irradiance.

Data-Driven Photovoltaic System Modeling Based on Nonlinear System Identification

Solar photovoltaic (PV) energy sources are rapidly gaining potential growth and popularity compared to conventional fossil fuel sources. As the merging of PV systems with existing power sources increases, reliable and accurate PV system identification is essential, to address the highly nonlinear change in PV system dynamic and operational characteristics. This paper deals with the identification of a PV system characteristic with a switch-mode power converter. Measured input-output data are collected from a real PV panel to be used for the identification. The data are divided into estimation and validation sets. The identification methodology is discussed. A Hammerstein-Wiener model is identified and selected due to its suitability to best capture the PV system dynamics, and results and discussion are provided to demonstrate the accuracy of the selected model structure.

Single‐switch single‐inductor multi‐output pulse width modulation converters based on optimised switched‐capacitor

To combine advantages of switched-mode and switched-capacitor (SC) power converters, a series of non-isolated multi-output pulse width modulation converters are developed in this study. This type of converters employs only one inductor and one active switch, which contributes to a simple structure and easy control features. An optimised SC technique is developed for peak current limitation and equivalent resistance reduction for SC units. Circuitry configuration, operation principle, equivalent model and an optimised design are presented in detail. Experimental results of a three-output (±24 V, 48 V) converter prototype verifies the feasibility of voltage regulation and power efficiency.

Integration of a series-pass device into switched-mode power converters for input harmonics filtering

A concept called the power semiconductor filter (PSF) is presented in this paper. It is used to perform input harmonics filtering for switched-mode power converters. The realisation of this concept is based on connecting a series-pass device (SPD) in series with the input of the converter, so that the input current of the entire system can be programmed by the SPD. The power dissipation of the SPD is maintained at a low level through a feedback mechanism that adjusts the input impedance of the converter and makes the voltage across the SPD small. The proposed concept has been applied to two applications: a 75 W, 90 V to 140 V/24 V classical buck converter and a 100 W, 90 V to 265 V/400 V power factor corrector (PFC). The results show that the PSF concept can significantly reduce the input current harmonics and improve the power factor with a conversion efficiency comparable to traditional passive filters. The major advantages of the PSF are that the filter section is amenable to monolithic integration and...

A Review on Stability Analysis Methods for Switching Mode Power Converters

In distributed power generation systems a pivotal role is played by DC-DC power converters that are employed to connect local loads to local power sources. These converters are used either in combinations of series/parallel connections or as stand-alone devices. A lot of work has taken place in the stability analysis of these converters and several methods have been used/proposed with different properties, strengths and weaknesses. Describing all existing methods is probably a never ending task and therefore in this tutorial paper four different methods will be presented by pointing out their main properties and explaining briefly how they can be used in applications that involve power converters. More specifically, the chosen methods are based on 1) the Poincare map, 2) Saltation matrix, 3) trajectory sensitivity, and 4) steady-state-response analysis of the discrete-time model. Simple case studies from previous publications are collected and presented in order to further explain these methodologies. Finally, this paper intents to describe some of the future challenges that exist in the area of stability analysis of power converters especially when these are employed in distributed generation applications.

Single-Switch Multichannel Current-Balancing LED Drive Circuits Based on Optimized SC Techniques

By combining the conventional switched-mode power converters with advanced switched capacitor (SC) techniques, a plurality of single-switch current-balancing circuits is developed to drive multiple light-emitting diode (LED) strings in this paper. Compared with the existing current-balancing LED drivers, the proposed drive circuits exhibit their attractive advantages in size and cost efficiency because just one active switch and one magnetic device are required. LED strings' current can be regulated by controlling the duty ratio of the switch in pulsewidth-modulation mode. Both advanced resonant and nonresonant SC methods are introduced to optimize the performance of the proposed LED drivers. The feasibility and theoretical analysis are verified with a 9-W dual-channel nonisolated prototype and a 25-W four-channel isolated prototype.

Investigating the Aging Effect of High Frequency Current Ripple on Lithium-Ion Cells

Within the field of electrochemistry, it is generally accepted that the rate of most electrochemical reactions do not exceed the 1 ms range. In other words, equilibrium perturbations with a frequency of more than ~1 kHz will not affect the chemical composition of a given system. For example, in the case of a lithium-ion cell a high frequency change in applied voltage would be expected to charge and discharge the electrochemical double layer without causing intercalation or deintercalation of lithium ions at either electrode. However, batteries are applied devices which can be found in virtually every field of technology imaginable. Experts from other fields do not view batteries from the same perspective as the electrochemist, and often ascribe to them preconceived properties which may not be accurate. As an example, the drive train in an electric vehicle includes a large capacitor, called a DC-link capacitor, between the switched mode power converter and the battery. The purpose of this capacitor is in part to shield the battery from residual AC harmonics, the frequency of which typically exceeds 1 kHz. If this shielding is unnecessary, the DC-link capacitor could be made significantly smaller which would simplify the entire drive train. In order to determine whether or not the current design of the DC-link capacitor is justified, we have built an experimental setup where twelve prismatic lithium-ion cells with a capacity of 25 Ah each will be exposed to a high frequency current ripple during cycling. The twelve cells will be divided into groups of three, where each of the four groups will be exposed to a different type of current ripple. All cells will be cycled with a rate of 1.6C (40 A), and the four groups will be exposed to ripple with a frequency of 100 Hz, 1 kHz, 10 kHz, and no ripple, respectively. Experiments will begin in May 2015 and run for at least one year, or until the cells under test reach their end-of-life, defined as having degraded to 70% of the original capacity or being unable to sustain a 5C power pulse for 10 seconds. The experiment will periodically be halted to perform characterization tests on the cells. In parallel with the experiments, a mathematical model describing the time dependent behavior of lithium-ion cells when exposed to high frequency perturbations will be created. The model will be experimentally verified using the results from the experiments. This project will show if the aging properties lithium-ion battery cell aging is negatively effected by high frequency current ripple, of the type commonly found in electrical vehicle drive trains. We hypothesize that the effect is lesser than is currently assumed when designing such systems. If so, it would the DC-link capacitor could be made smaller because it does not need to protect the battery from residual ripple from the power converter. In addition, it may be possible to synergistically use the battery's double layer capacitance to further reduce the size of the DC-link capacitor. A mathematical model which could be used to make such design decisions will be developed.

A Generalized Common-Mode Current Cancelation Approach for Power Converters

The interwinding parasitic capacitance of transformers and the parasitic capacitance between semiconductor switches and the ground are two major contributors to the common-mode (CM) noise currents in switched mode power converters. In this paper, a generalized CM current cancelation approach is proposed for the reduction of CM noise in isolated power converters. The approach is demonstrated in a forward converter. In this approach, the total effect of the two parasitic capacitances on CM noise is represented with an equivalent parasitic capacitance (EPC) at low frequencies. With this EPC, different CM current cancelation techniques can be efficiently organized to simultaneously cancel the low-frequency CM noise caused by these two parasitic capacitances. Furthermore, the EPC can be used to evaluate and quantify the performance of CM noise reduction techniques. Both theoretical analysis and experimental results show that the proposed approach is easy to implement and can significantly attenuate low frequency CM noise and therefore greatly reduce CM filter size and cost.

Theoretical modelling of the storage energy envelope of high frequency AC reactive components to predict chaos boundary

The storage energy of high frequency reactive component for the switched mode power converter is a new factor to assess the performance. The instability of the switched-mode converter under the peak current control mode is examined for its storage energy. Bifurcation and chaos of the storage energy in the inductor and capacitor are observed based on the stroboscopic map. The boundary of maximum storage energy is given to be an alternative to study the instability of the system in this study. Zero energy is obtained in stable period 1 and the storage energy with the same value and opposite direction is obtained in period 2. The simulation results of bifurcation and chaos of energy are obtained under different parameters and verified by experiment. The boundary of instability of energy stored in the reactive component under various parameters is formulated and a single equation can be used to indicate the factors. These results can provide a new guideline to design a stable system and provide a new control algorithm for power electronic system.

Circuit-Oriented Treatment of Nonlinear Capacitances in Switched-Mode Power Supplies

Nonlinear, voltage-dependent capacitances of power semiconductor devices are capable of having significant impact on the operation of switched-mode power converters. Particularly at high switching frequency, these nonlinearities play a significant role in determining switching times, losses, and converter dynamics during switching transitions. In order to accommodate the well-established design and analysis techniques commonly used for linear circuits, this paper examines the nonlinear voltage-dependence of switching device capacitances and proposes a circuit-oriented analysis technique that allows the parasitic capacitances to be replaced with linear equivalents. The multitude of developed equivalents are verified through full nonlinear simulation in both MATLAB/Simulink and SPICE, as well as through experimental results.

Total ionizing dose (TID) evaluation of magnetic tunnel junction (MTJ) current sensors

The paper shows an experimental study to know the behaviour of tunnel magnetoresistive effect-based current sensors configured in a Wheatstone bridge in response to irradiation. In particular the sensitivity, hysteresis, output offset voltage and input resistance are discussed when the sensors are submitted to a total irradiation dose of 43krad with 36krad/h dose rate. The same electrical parameters were studied subsequently once the irradiated sensors were submitted to an 80°C annealing process. The studied TMR sensors are applied in a switched-mode power converter for space application.

Power high-voltage and fast response Schottky barrier diamond diodes

We developed and investigated a set of packaged vertical diamond Schottky barrier diodes (SBDs) with a large crystal area of up to 25mm2. All devices show forward current above 5 A and the blocking voltage over 1000V in the temperature range from 20°C to 250°C. Due to the large crystal area and finite thermal resistance of the crystal-case interface the forward current self-heating effect results in a good diamond SBDs performance not only at elevated temperatures but also at normal conditions. As a result we measured about 4V forward voltage drop, 35mΩ×cm2 specific on-resistance and 100nA/cm2 leakage current for the diode case at room temperature. At a case temperature of 250°C the forward voltage drop was less than 2.5V, the specific on-resistance about 40mΩ×cm2 and the leakage current about 100μA/cm2. The Baliga's figure of merit was 25–30MW/cm2 in the temperature range of 20-250°C. The typical value of the reverse recovery time less than 10ns while switching from 2A forward current to 100V blocking voltage meets the requirements for practical use of diamond SBDs in effective switch-mode power converters operating at frequencies higher than 1MHz. Further device design optimization and the diamond epitaxial layer quality improvement will help to reduce the power losses in on-state and make diamond SBDs competitive with SiC diodes even at room temperature.

Developing dead-beat control in a valve electric drive

Problems of constructing high-speed control systems of electric drives with switch-mode power converters are discussed in the present paper. Historical aspects of the development of these theoretical issues at the Department of Automated Electric Drives of the Moscow Power Engineering Institute and their importance are discussed. The described converters are control objects of a discrete type that should be considered in the creation of control systems. It is shown that dead-beat control in such systems in the unconstrained case makes a finite number of discreteness intervals equal to the system order. Two currently important principles in construction of a dead-beat control system—namely, ones using predictive models in a real and accelerated time scale—are considered. Since the operation quality of such systems is determined by the adequacy of the predictive model of the control object, the approaches to creating the self-adjustment algorithms allowing one to correct the model in operation are considered.