Comparison of Interleaving Methods of Parallel Connected Three-Level Bi-Directional Converters

The voltage and current ripples in the three-level bi-directional converter (TLBC) can be reduced by an interleaving technique that controls a phase difference between the modules of power converter. On the other hand, the inductor current ripple in TLBC is increased due to the circulating current between the modules. In this paper, the effects of two interleaving methods on a two-phase TLBC, Z-type and N-type, are investigated and compared. In particular, capacitor current ripple, and voltage ripple are compared by two interleaving methods verified through Powersim (PSIM) simulation.

Facies Composition and Stratigraphic Position of the Quaternary Upper Yenisei Sequence in the Tuva and Minusa Depressions

—The paper concerns the sediment sequence, which is widespread in the Yenisei valley and in the Tuva and Minusa depressions and also present in the valleys of the southern Chulym plain. The sediments of this sequence were previously described as “Neogene mud-shedding”, as well as moraines, alluvial fan deposits, alluvium of Middle Pleistocene high terraces, and lacustrine sediments. The giant ripple marks on the Upper Yenisei terraces was commonly interpreted as ribbed moraines; however, in recent studies, these ridges have been repeatedly referred to as marks of giant current ripples. Besides, some recently published papers provide description of geology of this sequence fragments suggesting its deposition by cataclysmic floods. Geomorphological analysis of the area shows Pleistocene glaciers to have been localized within the medium–high mountainous areas. The glaciers did not reach the Tuva and Minusa depressions and occupied large areas only in the Todzha basin and on the periphery of the Darkhat basin, forming a glacial dam at its outlet, which resulted in glacial-dammed lakes filling the basin completely. These lakes outburst, and the resultant flooding led to the deposition of megaflood sediments, which we refer to here as the Upper Yenisei sediment sequence. A detailed analysis of its facies architecture revealed similarity of these sediments to those of the Sal’dzhar and Inya sequences in Gorny Altai. Most of the Upper Yenisei megaflood sediments are localized in topographic lows of the Tuva and Minusa depressions. Beyond the Altai–Sayan mountainous area, the megaflood sediments of the Upper Yenisei sequence compose high terraces of the Yenisei, Chulym, Chet’, and Kiya rivers in the southern Chulym plain. The formation of Upper Yenisei sequence dates to the first half of the Late Pleistocene, inasmuch as it contains inset alluvial sediments of the second terrace of the Yenisei River. The available data allow suggesting that the Upper Yenisei sequence formed in the first Late Pleistocene regional glaciation. The Sal’dzhar sequence in Gorny Altai and the fourth terrace of the Ob’ River on the Fore-Altai plain are stratigraphic analogs of the Upper Yenisei sequence. The Upper Yenisei and Sal’dzhar sequences can thus be considered future regional markers serving as a link for the local stratigraphic schemes of the Altai–Sayan mountainous area and adjacent West Siberian plains. The results obtained call for verification by geochronological dating, first of all, by modern luminescence dating methods covering a wider chronological interval than radiocarbon dating.

Cascaded Voltage and Current Control for a Dual Active Bridge Converter with Current Filters

The paper describes the cascaded voltage and current control for a bidirectional DC/DC converter in Dual Active Bridge (DAB) topology. The typical DAB converter circuit was extended by additional current filters, which allow it to operate in application fields with high requirements on current ripples. The core concept of the presented solution is usage of the modified Single Phase Shift (SPS) modulation, which allows to compensate for the DC-bias current occurring in dynamic states and provides a settling time of half switching cycle during transients. Its features were utilized to build a simplified dynamic model of the converter. The linear Proportional-Integral (PI) controllers are used in both voltage and current control loops. Based on the developed dynamic models, the tuning rules for both controllers were derived. In both cases, a number of the tuned parameters were reduced from two to one (which can present a great practical value for application engineers). The proposed solutions are validated based on a laboratory prototype. An important part of the experiments was devoted to non-linear effects occurring near the current limitation boundary of the system. The paper ends with a brief discussion regarding the future research directions.

TORQUE RIPPLE REDUCTION OF A BRUSHLESS DC MOTOR USING Y-SOURCE CONVERTER

The brushless DC motor (BLDC) is a low cost, reliable and efficient motor for low power applications. In general, the speed, torque and current of the BLDC motor are controlled using a well tuned PI controller in the inner and outer control loops. This controller will be effective in reducing the dynamic speed error, but will produce large current ripples. This reference current when given to the inner control loop and controlled using hall-effect position sensing technique, leads to comparatively large ripples in the torque. Because of large dynamic behavior of dc link voltage when nominal rating capacitor is used, there will be torque ripples and reduction in rotor speed from the reference current value. Hence, to mitigate this torque ripples in BLDC motor a fast acting adjustable dc link voltage like chopper is generally used. The effective dc link voltage control with voltage boosting and controlling action is observed with Y-source converter and is compared with a Z-source converter in this paper. The Y-source converter is designed in such a way that, it will effectively control the speed and also produces lesser current ripples reference. Further, the inverter topology uses a six switch basic configuration but with a new switching strategy. The results are compared with a Z-source converter with the proposed Y-source converter under variable load torque and variable speed cases in MATLAB/ SIMULINK environment. It is found that, the torque ripples are reduced effectively without much change in the reference speed. Also, even at higher rotor speeds, the torque ripples and surges are also lesser.

Important Technical Considerations in Design of Battery Chargers of Electric Vehicles

There are many important trade-offs and constraints on cost, volume, weight, conduction losses, switching losses, microcontrollers, isolation, voltage and current levels, voltage and current ripples, battery specifications, charging–discharging algorithms, control system, switch gate drivers, and efficiency of battery chargers in electric vehicles. In this paper, a well-known power electronic topology commonly used in recent relevant studies is considered, and some important technical considerations with regard to the mentioned trade-offs and constraints are discussed in detail for the first time. The discussion concerns the practical and theoretical experiences in implementation of battery chargers and charging stations of electric vehicles exclusively, and it can be extended to various other power electronic topologies.

DC-Link Current Harmonic Mitigation via Phase-Shifting of Carrier Waves in Paralleled Inverter Systems

DC-connected parallel inverter systems are gaining popularity in industrial applications. However, such parallel systems generate excess current ripple (harmonics) at the DC-link due to harmonic interactions between the inverters in addition to the harmonics from the PWM switching. These DC-link harmonics cause the failure of fragile components such as DC-link capacitors. This paper proposes an interleaving scheme to minimize the current harmonics induced in the DC-link of such a system. First, the optimal phase-shift angle for the carrier signal is investigated using the analytical equations, which provides maximum capacitor current ripple cancellation (i.e., at the main switching frequency harmonic component). These optimally phase-shifted switching cycles lead to variations of the output current ripples, which, when summed together at the DC-link, result in the cancellations of the DC-link current ripples. The results show that when the carrier waves of the two inverters are phase-shifted by a 90° angle, the maximum high-frequency harmonic ripple cancellation occurs, which reduces the overall root-mean-square (RMS) value of the DC-capacitor current by almost 50%. The outcome of this proposed solution is a cost-effective DC-harmonics mitigating strategy for the industrial designers to practically configure multi-inverter systems, even when most of the drives are not operating at rated power levels. The experimental and simulation results presented in this paper verify the effectiveness of the proposed carrier-based phase-shifting scheme for two different configurations of common DC connected multi-converter systems.

MODIFIED QUADRATIC BUCK BOOST CONVERTER FOR PV APPLICATIONS

Buck-boost DC/DC converters have been extensively employed in stepping up/down the voltage for PV applications. The input and the output port current of the traditional quadratic buck-boost converter are discontinuous, which result in increased input and output current ripples and complicate the design of the input and output filters. Hence these problems can be solved by using a modified quadratic buck boost converter, which provides wider voltage conversion ratio with continuous input and output ports current. Dual output can be derived from this single input converter for multiple output applications. Also a fuzzy logic controller can be designed for this proposed converter for better and faster performance.