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A new feed-forward control technique for a dc–dc step-up converter based on the asymmetric multistage stacked boost architecture (MSBA) is proposed. The developed feed-forward controller directly handles the load current and the perturbations that may be caused by the dynamic operation of the converter. Thus, there is no time delay for estimating the error in a control process, and therefore, both robust steady-state operation and high dynamic performance can be achieved. The asymmetric MSBA dc–dc converter is a single-output high-voltage topology that embodies several in-series active voltage-balancing circuits. Thus, there is a need for an improved balancing control method. This can be accomplished by replacing the conventional proportional-integral controllers with feed-forward type and therefore improved balancing between the stages can be attained, because the steady-state errors are suppressed and the dynamic response can be enhanced. A thorough theoretical analysis is conducted for verifying the stability of the suggested feed-forward control technique in an asymmetric MSBA converter, and selective simulation and experimental results are demonstrated in order to validate the effectiveness and feasibility of the proposed control scheme. [ABSTRACT FROM PUBLISHER]

The grid-connected modular multilevel converter (MMC) is very likely to operate under asymmetric grid conditions. Such a converter features several unique characteristics, which make its analysis different from other types of power converters in similar cases. In this paper, the three well-established control techniques, i.e., balanced current and negative sequence current injection for active/reactive power oscillation elimination, are tailored for the MMC case taking into account grid current limitation under fault conditions. Since the focus is laid on the MMC design impact during grid asymmetries, the three methods are compared in terms of branch energy variation increase as well as maximum achievable active power transfer. Moreover, the effect of circulating current second-order harmonic injection for capacitive storage reduction as well as dc-link oscillation elimination is also studied. Finally, experimental results from a downscaled laboratory prototype verify the theoretical studies. [ABSTRACT FROM PUBLISHER]

Multilevel converters and battery energy storage systems are key components in present and future medium voltage networks, where an important integration of renewable energy sources takes place. The modular multilevel converter offers the capability of embedding such energy storage elements in a split manner, given the existence of several submodules operating at significantly lower voltages. This paper analyzes such a converter structure under different operating modes. In order to eliminate the low-frequency components of the submodule output currents, the latter are interfaced to the batteries by means of nonisolated dc/dc converters. Control algorithms are developed for the balancing of the battery state of charges and the respective gain limitations are established. Unbalanced grid conditions are also taken into account through the theory of symmetrical components and solutions are proposed. Finally, the development of a down-scaled prototype is described and experimental results are presented. [ABSTRACT FROM AUTHOR]

In this paper, the analytical solution for the submodule voltage ripple equations of a modular multilevel converter (MMC) is derived, based on the knowledge of the external voltage/current magnitudes, and enhancing a concept previously presented in the literature. In order to achieve high accuracy, all passive elements of the converter, common-mode voltage injection as well as intentionally imposed circulating current harmonics are taken into consideration. The natural charge level mechanism of the capacitor voltages is also explained. As application examples, the three- as well as the two-phase grid-connected MMC cases are chosen. The control of line and circulating currents is also discussed and two respective independent feedback loops are formed. The concept of fictive-axis emulation is tailored for the two-phase MMC case, in order to achieve vector control of the line current and therefore straightforward desired injection of active and reactive power. Finally, the development of a reduced-scale laboratory prototype is presented and a full set of experimental results are provided, verifying the aforementioned concepts. [ABSTRACT FROM AUTHOR]

This paper presents a preliminary work on the feeding of an ac dipole using a resonant circuit with a varying resonant frequency. A single-phase LC oscillator containing a variable capacitor is fed by a wideband amplifier or a voltage source inverter. For this purpose, a bank of switched capacitors of different values are connected to the main circuit through bidirectional switches. In order to allow zero-current and zero-voltage switchings, the devices are implemented with close-control driver circuits, allowing self-switching based on local polarity measurements. An innovative controller for maintaining the current in an oscillator and a regressive method for measuring alternating current with a limited number of samples are proposed and validated by experiment. [ABSTRACT FROM AUTHOR]

Multilevel inverter applications have become more and more common. Multilevel topologies have now to serve new purposes, and interest is rising in new application fields. Recent multilevel technologies have the potential to significantly reduce the size of passive filters, thus increasing efficiency and power density. With the more stringent regulations concerning harmonic emissions and reliability concerns, more levels are needed to allow filterless operation while keeping a moderate switching frequency and simple structure. In this context, the new topological family of high-density advanced multilevel inverters, called cross-connected intermediate-level voltage source inverter, is introduced in this paper. [ABSTRACT FROM AUTHOR]

Rising interest in multilevel applications has triggered new research activities. This paper proposes a novel multilevel power electronics building block (PEBB) for the five-level active neutral point clamped (ANPC) multilevel voltage source inverter. The PEBB is composed of six switches in a crossed configuration and one capacitor. It is common to the three phases of a five-level ANPC topology, enabling a large number of levels to be generated. This PEBB is meant to be a reliable upgrade to the 5L topology, increasing output signal quality and reducing the size of the output filter in medium voltage applications. The number of levels generated by the common cross-connected stage (C³S) PEBB and the ANPC depends on the voltage ratios chosen between the phase capacitors of the ANPC and the PEBB capacitor(s). The tradeoff stands between the ability to balance the capacitors, the rated blocking voltage of the devices, and the number of levels produced. Under a given configuration, nine levels can be produced, with the possibility to balance the capacitors up to modulation indexes in the region of m = 0.92. The analysis of the general topology, the description of the nine-level case, and simulation results are first presented. Prototyping results are then shown, and they validate the introduced concept and topology. [ABSTRACT FROM AUTHOR]

In addition to the high-capacity storage facilities based on hydropower technologies, electrochemical solutions are today's candidate for storage for renewable energy sources support. However, sustainability and limited life cycles of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, which is mainly based on compressed air, where the storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted mean power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. This paper describes the concept of the system, the power-electronic interface circuits, and especially the maximum efficiency point tracking (MEPT) algorithm and the strategy used to vary the output power. In addition, this paper presents the characteristics of high-efficiency storage systems where the pneumatic machine is replaced by an oil-hydraulic and pneumatic converter, which is used under isothermal conditions. Practical results are also presented, which are recorded from a low-power pneumatic motor coupled to a small dc generator as well as from the first prototype of the final hydropneumatic system. [ABSTRACT FROM AUTHOR]

In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage industrial drives. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level integrated gate-commutated thyristor inverter (main inverter), with a two-level insulated-gate bipolar transistor H-bridge (subinverter) in series with each phase. To keep the power part simple and the efficiency high, the subinverters have no feeding from the net and can only supply reactive power. This is a very interesting solution in terms of power quality, efficiency, reliability, and cost. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an online nonlinear model-predictive controller. The con- troller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to find the optimal control to apply to the system. Simulations and measurements demonstrate stable behavior in steady state and during transients. Precharging of the nonsupplied capacitors is also an issue to consider. This paper proposes a startup method that charges them in parallel with the supplied ones, without any additional equipment. Measurements show its successful application in the proposed drive system. [ABSTRACT FROM AUTHOR]

A new feeding concept for electrical transportation systems is presented, based on supercapacitive energy storage. Supercapacitors are new and powerful components for energy storage. Compared with batteries, the amount of energy supercapacitors can store is low and does not allow large vehicle autonomy. Because supercapacitors have the property to be re-loadable in a few seconds, a sequential supply system has been developed, considering repetitive feeding at the stops. To solve the problem of the high power amount needed to reach short refill times, a solution is proposed, which consists of using an intermediary supercapacitive tank placed at fixed stations, which is refilled between the bus arrivals with a much lower power. In addition to the description of the needed power electronic converters, theoretical and experimental results are presented, defining the controlled profile of the instantaneous power level, in order to achieve a fast energy transfer between two supercapacitive tanks. [ABSTRACT FROM AUTHOR]

Presents how supercapacitors can be used for power smoothing in elevator applications in comparison with other conventional solutions using resistive or regenerative breaking. Applications of supercapacitors in the field of energy storage; Strategy for capacitive energy storage; Power requirements of elevators; Principle of the high-efficient soft-commutated power converter.