Switched-mode Power Converters Research Articles

Hybrid-modulation-based control technique for reduction of output voltage ripples in frequency-modulated switch-mode power converters

<span>In this paper a novel control technique for switching-frequency-modulated switch-mode power converters (SMPC) operating in discontinuous conduction mode is proposed. The use of the technique leads to significant reduction in peak-to-peak output voltage and peak currents increased due to straightforward application of switching frequency modulation (SFM). The technique is based on hybrid modulation scheme in which both switching frequency and duty ratio are modulated simultaneously by the same modulation signal. Theoretical analysis and experimental verification of the proposed technique are presented in details. Both computer simulations and experiments show that switching-frequency-modulated SMPC with the proposed control technique in comparison to SMPC without SFM has appreaciably lower conducted electromagnetic emissions, at the cost of slightly increased peak-to-peak output voltage and peak currents.</span>

An Aperiodic Modulation Method to Mitigate Electromagnetic Interference in Impedance Source DC–DC Converters

Rapid voltage and current transitions in switched-mode power converter circuits generate electromagnetic interference (EMI) which may interfere with other electronic systems. High-speed (e.g., wide bandgap) switching devices can improve circuit efficiency and compactness, but may increase the bandwidth of the interference generated. The peak interference is concentrated at harmonics of the fundamental switching frequency, and so may be reduced by modulating the converter switching frequency. However, converter topologies incorporating more than one switching device may not be suited to modulation of the switching frequency, and coordinated modulation of other pulse parameters is required to suppress interference. A relatively simple implementation of a hybrid pulse modulation technique is presented to suppress EMI in a quasi-Z-source converter comprising an impedance-source network and GaN-based H-bridge switching circuit. The technique uses two anharmonically related periodic signals to generate a modulated sawtooth carrier, which in turn generates coordinated switching pulses aperiodically modulated in position and width within a constant switching period. Experimental results demonstrated 10 dB suppression of the peak interference with negligible impact upon the converter's efficiency or output voltage. The proposed pulse modulation technique and its method of implementation are generic, and are expected to be widely applicable to other switched-mode dc–dc power converters.

Undersampling Control for a DC–DC Boost and Forward Dual Active Bridge for a Single-Phase Grid-Connected PV Converter

Digital control methods and digital controllers are widely adopted in power electronics applications due to technical and economic advantages against its analog counterparts. Switched-mode power converters with switching frequencies of hundreds of kilohertz to megahertz impose a challenge such as less sampling time in which control algorithm calculations must be realized in digital implementations. Software-based controllers are designed and implemented in code lines executed in general-purpose DSP, being the most preferred digital implementation. Although high-frequency applications with more complex algorithm calculations restrict the maximum allowable sampling frequency, that can be even below the converter switching frequency. The study, analysis and design in such special condition is a main contribution of the paper. Without loss of generality, a software-based digital design under processing speed limitation is developed for two DC–DC power converters that compose a single-phase grid-connected PV converter: (1) a boost converter and (2) a unidirectional power flow DAB topology.

Enhanced Power Output from the PV with Low Input Ripple DC-DC Converter

The primary objective of Maximum Power Point Tracking (MPPT) for PV systems connected to a low-voltage DC grid is to extract the maximum possible power output from the PV array. Normally high-frequency switched mode power converters are employed to track the maximum power. These converters, however, impose switching frequency voltage ripple on the PV output. This causes fluctuation around the Maximum Power Point (MPP) and results in power loss. These losses can be reduced using electrolytic capacitors, however, the electrolytic capacitors’ lifespan is relatively shorter than that of a PV panel. In this paper, an interleaved boost converter is used to reduce high-frequency voltage ripple introduced on panel. Hence, smaller values of longer lifespan capacitors such as film capacitors will be sufficient to curtail the smaller ripple. Moreover, film capacitors are selected based on voltage ripple. Analysis was carried out for calculating voltage ripple imposed on PV module to select input filter more precisely. In addition, reduction in the voltage ripple is calculated quantitatively and is compared with that of a conventional boost converter. Enhanced power output from the PV panel is mathematically proven and experimentally demonstrated.

Computationally Efficient Self-Tuning Controller for DC–DC Switch Mode Power Converters Based on Partial Update Kalman Filter

In this paper, a partial update Kalman Filter (PUKF) is presented for the real-time parameter estimation of a dc–dc switch mode power converter. The proposed estimation algorithm is based on a novel combination between the classical Kalman filter (KF) and an M-Max partial adaptive filtering technique. The proposed PUKF offers a significant reduction in computational effort compared to the conventional implementation of the KF, with 50% less arithmetic operations. Furthermore, the PUKF retains comparable overall performance to the classical KF. To demonstrate an efficient and cost effective explicit self-tuning controller, the proposed estimation algorithm (PUKF) is embedded with a Banyasz/Keviczky proportional, integral, derivative (PID) controller to generate a new computationally light self-tuning controller. Experimental and simulation results clearly show the superior dynamic performance of the explicit self-tuning control system compared to a conventional pole placement design based on a precalculated average model.

Bidirectional DC-DC Converter Systems: Sustaining Power Component Design Methodology to Achieve Critical Power Conditioning

Converting interchangeable loads and sources on committed power interconnect is becoming more commonplace in the art of switch-mode power design. Simple, robust schemes have ended up serving in strategically important applications such as those in the dc bus system of NASA's International Space Station and in the more familiar world of automotive hybrid electric vehicles [1], [2]. As more diverse sources of energy lend themselves to economical and efficient conversion into electricity, the need to streamline the delivery of electrical power from one dc potential to another becomes more apparent. Switched-mode power conversion is a well-established means of achieving high-efficiency dc regulation. It has been found that making adaptations to a proprietary switched-mode resonant topology results in the achievement of a reliable, high-performance bidirectional converter (BDC). The flexibility BDCs offer in numerous applications brings significant economic and operational outcomes.

A general software package for modelling a contact-less electric-vehicles battery-charging public-station fed from on-grid photo-voltaic array

The development and commercialization of hybrid electric vehicles (HEVs) and electric vehicles (EVs) are actively being realized due to environmental concerns and rising oil prices. But, EV technology with battery has faced many problems up to now. One of the most important problems is rapidly battery-charging from a clean and reliable source. So, this research proposes a convenient way to charge batteries of EVs and HEVs from a neat power supply. The paper introduces a public off-board battery-charging station fed from on-grid (OG) photovoltaic (PV) array. The proposed 100kW-contactless charging station is modelled, and simulated. It comprises two main sections: station-side (stationary) section and EV (moving) section. The first section includes PV panels, maximum power point tracking (MPPT)-converter, on-grid 3-level interface inverter, and high-frequency compensated resonant converter. The other section consists of the rectifier, switched mode power converter, and battery-charging controller. An inductive-coupled power (ICP) is transferred from the station to the batteries through an air-core transformer (ACT) with large air-gap. Its primary winding is placed on the station ground and the secondary winding is in the EV. Modelling of the ACTs accomplishes several requirements such as air-gap, have good tolerance to misalignment, light-weight, durable and cost effective as possible. Smart and intelligent controllers are proposed for MPPT, interface on-grid inverter and battery-charging converter. Simulation results are obtained using a Simulink/m-file software package helping in modelling of battery-charging public station.

Dynamic RON Characterization Technique for the Evaluation of Thermal and Off-State Voltage Stress of GaN Switches

GaN power switches provide remarkable performance in terms of power-density, reduced parasitics, and high-thermal handling capability that enable the realization of very efficient and compact dc/dc converters. Despite exhibiting state-of-the-art channel conductivity, GaN high electron mobility transistor (HEMT) devices are affected by the degradation of the dynamic on -Resistance ( R ON) at increasing off -state voltages and operative temperatures. In this paper, a novel laboratory setup and characterization procedure for the dynamic R ON of GaN HEMT switches in the presence of thermal- and trapping-effects is presented. The proposed setup allows the study of R ON transients after the switching event at variable off -state voltages and temperatures. The use of custom-designed differential amplification stages and a voltage-controlled current source enables the accurate characterization of R ON even on large periphery devices. At first, the proposed setup is tested with a well-established and mature device technology such as a Si MOSFET. Degradation of the R ON up to 120% due to temperature variation is observed with the presented setup. The setup is then used for the characterization of commercial-grade GaN-on-SiC and GaN-on-Si HEMTs. For both technologies dynamic R ON degradations up to 75% and 20% are observed for temperature and off -state voltage variations, respectively. These characterization data are fundamental for the accurate estimation of conduction losses during the design of switching-mode power converters.

Adaptive dynamic voltage transitioning in switch mode DC–DC power converters

Higher transistor density in modern processors leads to an increase in computing power, which results in higher power consumption. To combat this, system‐level power saving features like dynamic voltage transitions (DVTs) are introduced where the voltage required by the processor is varied according to computational load. In commercially available systems, the slew rate of the voltage transition is limited, which has the negative effect of increasing computational latency to ensure safe operation of the switch mode power converter. This study addresses the limitations of the existing techniques by introducing an adaptive DVT, which enables finer granularity of the operating voltage levels and promotes greater power savings. The switching surface‐based analysis is performed to derive the conditions for (near) optimal voltage transitions constrained by inductor saturation limits. The results of an experimental prototype achieving the fastest safe transition response are shown to correlate well with the analysis across a wide range of DVT conditions.

Ferrite Paste Cured With Ultraviolet Light for Additive Manufacturing of Magnetic Components for Power Electronics

Additive manufacturing (AM) has the potential to rapidly prototype innovative designs of magnetic components aimed at improving power density and efficiency of switch-mode power converters. However, only a few magnetic feedstocks are available for AM, and the fabricated parts have significantly poorer magnetic properties. Our previous studies showed the promise of an extrusion-based AM platform for making high-performance power magnetics. But, the magnetic paste feedstock developed in these studies suffered from the “slumping” problem, thus not suitable for building large or tall core structures. To improve the AM capability, a ferrite paste was developed that is cured upon ultraviolet (UV) illumination. Core structures with large aspect ratios were fabricated by retrofitting the printer with a UV-light-emitting diode module. By varying the magnetic composition of the paste and sintering the printed parts at and below 1000 °C, we made tall (>4 mm) ferrite cores with relative permeability ranging from 63 to 103 and resonance frequency higher than 30 MHz.

On spintronics-based nano-scale power electronics

It is suggested to explore achievements in spintronics for future design of nanoscale power converters. In contrast with traditional semiconductor switch-mode power converters, spintronics based power conversion may be achieved without repetitive (high-frequency) switching.

Bifurcation Phenomena and Stabilization With Compensation Ramp in Converter With Power Semiconductor Filter

A concept, named as power semiconductor filter, has been demonstrated to be an alternative to perform input harmonic filtering in switched-mode power converters. It utilizes a series pass device (SPD) to profile the wave shape of the supply current, while the voltage across the SPD is regulated at a threshold voltage between the linear and saturation regions of the SPD to minimize its power dissipation. Bulky passive components for input harmonic filtering can then be eliminated or shrunk with such active supply current control. For the sake of circuit elegancy, regulation of the SPD voltage is realized by a bang-bang (peak-voltage) controller to vary the input characteristics of the power conversion stage through adjusting some control parameters, such as duty cycle and switching frequency. Experiments reveal that the entire system might exhibit bifurcation phenomena under some supply and load conditions. This paper will derive a sampled-data model to characterize such system behaviors and to identify the onset of bifurcation and chaos. A compensation ramp will be proposed to introduce into the bang-bang controller to stabilize the system operation. Moreover, the slow-scale dynamics will be studied with small-signal models. The investigations will be exemplified on a 48 W, 40–140 V/24 V buck dc–dc converter prototype.

Impact of PWM Duty Cycle Jitter on Switching-Mode Power Converter Efficiency

The objective of this paper is to propose an efficiency model to evaluate the impact of the pulse width modulation (PWM) duty cycle jitter on the efficiency of switching-mode power converter. By taking the product of two perturbation terms into consideration, which is ignored in the conventional average small-signal model, the average efficiency model is proposed first. Due to the nonlinear characteristic of the PWM generator, the multifrequency efficiency model is also developed by considering the sideband frequency. Three different perturbation waves are induced to the control loop of the converter to generate the jitter to observe its impact on the efficiency. The mathematical expression of the efficiency drop based on the proposed multifrequency model is derived. The reason of control-to-output gain's magnitude spike on the Bode plot can be explained by the derived equations. Eventually, the methods to reduce the efficiency drop caused by the jitter are suggested. In spite of various perturbation frequencies, amplitudes, and waveforms, the mathematical calculation, the computer simulation, and the hardware measurement of the efficiency drop are consistent which validate the accuracy of the proposed multifrequency efficiency model.

THD minimisation of multilevel inverter with optimised dc sources magnitude and switching angles

Multilevel inverter is a power electronic device that has many attractive features such as high-voltage capability and near sinusoidal output making them suitable for high-power applications. On the other hand, harmonic distortion from the modern switching mode power converters has become a serious problem in utility. Total harmonic distortion (THD) minimisation is a complex problem with multiple minima. Various THD minimisation methods have been proposed in studies that just optimise the switching angles of the multilevel inverter. In this study, both dc input sources magnitude and switching angles are optimised with particle swarm optimisation (PSO) algorithm to minimise the THD of the output staircase voltage of the multilevel inverter. The impact of the proposed minimisation method on voltage magnitude optimisation and increased number of switching angles optimisation on the staircase output voltage is analysed. The effectiveness of the proposed method is validated by simulation results of a seven-level inverter. The THD, output voltage level and number of the switching angles of the proposed method are compared with other techniques and influence of the input dc sources optimisation on the THD minimisation is shown.

Nonlinear Analysis and Control of Interleaved Boost Converter Using Real-Time Cycle to Cycle Variable Slope Compensation

Switched-mode power converters are inherently nonlinear and piecewise smooth systems that may exhibit a series of undesirable operations that can greatly reduce the converter's efficiency and lifetime. This paper presents a nonlinear analysis technique to investigate the influence of system parameters on the stability of interleaved boost converters. In this approach, Monodromy matrix that contains all the comprehensive information of converter parameters and control loop can be employed to fully reveal and understand the inherent nonlinear dynamics of interleaved boost converters, including the interaction effect of switching operation. Thereby not only the boundary conditions but also the relationship between stability margin and the parameters given can be intuitively studied by the eigenvalues of this matrix. Furthermore, by employing the knowledge gained from this analysis, a real-time cycle to cycle variable slope compensation method is proposed to guarantee a satisfactory performance of the converter with an extended range of stable operation. Outcomes show that systems can regain stability by applying the proposed method within a few time periods of switching cycles. The numerical and analytical results validate the theoretical analysis, and experimental results verify the effectiveness of the proposed approach.

Predicting Core Losses Under the DC Bias Based on the Separation Model

Magnetic components in switched-mode power converters usually work under the rectangular voltage excitations with a dc premagnetization; the nonlinear changing characteristics of core losses in the magnetic components are hard to predict. In this paper, the method for predicting core losses in power inductors is introduced. A simplified hysteresis loss model is proposed to explain the well-known empirical characteristics of the hysteresis loss. If the working conditions of the dc bias and flux density are the same, hysteresis losses will keep constant independent with the exciting voltage waveforms, and the values of eddy-current losses will also have the constant mathematics relationships between nonsinusoidal voltage excitations and sinusoidal voltage excitations. The proposed method is very practical since it only takes core loss data under the sinusoidal voltage excitations as inputs rather than relies on any material parameters. Core losses under the different duty cycles and premagnetization levels have been tested; the experimental results verify the correctness of the proposed model.

A simple effective heuristic for embedded mixed-integer quadratic programming

ABSTRACTIn this paper, we propose a fast optimisation algorithm for approximately minimising convex quadratic functions over the intersection of affine and separable constraints (i.e. the Cartesian product of possibly nonconvex real sets). This problem class contains many NP-hard problems such as mixed-integer quadratic programming. Our heuristic is based on a variation of the alternating direction method of multipliers (ADMM), an algorithm for solving convex optimisation problems. We discuss the favourable computational aspects of our algorithm, which allow it to run quickly even on very modest computational platforms such as embedded processors. We give several examples for which an approximate solution should be found very quickly, such as management of a hybrid-electric vehicle drivetrain and control of switched-mode power converters. Our numerical experiments suggest that our method is very effective in finding a feasible point with small objective value; indeed, we see that in many cases, it finds the global solution.

An Input Current Ripple-Free Flyback-Type Converter With Passive Pulsating Ripple Canceling Circuit

In order to solve the problems caused by the pulsating current ripple of switching-mode power converters, a passive pulsating ripple canceling circuit (PPRCC) is proposed in this paper. The features of the proposed PPRCC include simple, modular structure, and high degree of design flexibility. By integrating the proposed PPRCC, an input current ripple-free flyback-type converter is adopted and analyzed as an example because of its comprehensive utilization in small power rating commercial products. In addition, the switch voltage spike of flyback converter can be suppressed by integrating the proposed PPRCC without using snubbers, it turns out that the efficiency can be further improved. The corresponding operating principle, steady-state analysis, and zero ripple design criteria of the proposed PPRCC are provided. Finally, a 100 W laboratory prototype is constructed to verify the effectiveness of the proposed principle. Experimental results show that the resulting peak-to-peak input current ripple is reduced by 96% and nearly 0.5% and 1.7% improvement in efficiency can be achieved by the proposed PPRCC, at 80 W and 100 W load conditions, respectively.

Study of complex dynamics of DC-DC buck converter

Switched-mode power converter circuits are non-linear and time varying in nature. In this work, non-linear dynamics for both voltage- and current-mode-controlled DC-DC buck converter has been investigated through simulation and practical study. The converter is controlled by naturally sampled constant frequency pulse width modulation signals in continuous conduction mode and converter exhibits fundamental, subharmonics and chaotic oscillations for the variation of circuit parameters. In computational study, the model of buck converter is simulated by non-autonomous differential equations and finally the computational waveforms have been verified with experimental results. Here, the main objective of this research work is to study the experimental chaos and to identify the subharmonic and chaotic oscillation zones for specific parameter values that will help the power electronic engineers to design chaos-free power supply. It has been observed that the route to chaos is achieved by period doubling in the buck converter. In order to verify the computational study, laboratory prototype of closed-loop buck converter has been fabricated. The results obtained from simulation and experimental study have been presented and compared.

Estimation of Parasitic Resistance of Electrolytic Capacitor and Filter Inductor and Prediction of Input Filter Induced Oscillations in a Switch-Mode Magnet Power Supply

In switch-mode power converters with large ratings, it is important to be able to predict the parasitic resistances associated with circuit elements such as electrolytic capacitor and filter inductor in the initial converter design stage itself to avoid the cost and time associated with actual design, prototype fabrication, and testing of these components. Knowing the values of parasitic elements is also important as they decide the possibility of closed-loop instability, besides affecting the other circuit parameters. In this paper, a way to estimate the equivalent series resistance of electrolytic capacitor and the winding resistance of filter inductor is proposed leading to their closed form expressions in terms of system parameters. Using these, procedure to predict the closed-loop instability induced due to the input filter is exemplified with illustrative calculations.