There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

This paper summarizes recent contributions in the broad area of energy harvesting wireless communications. In particular, we provide the current state of the art for wireless networks composed of energy harvesting nodes, starting from the information-theoretic performance limits to transmission scheduling policies and resource allocation, medium access, and networking issues. The emerging related area of energy transfer for self-sustaining energy harvesting wireless networks is considered in detail covering both energy cooperation aspects and simultaneous energy and information transfer. Various potential models with energy harvesting nodes at different network scales are reviewed, as well as models for energy consumption at the nodes.

/pdf/energy-harvesting-wireless-communications-a-review-of-recent-22doeox995.pdf

Energy Harvesting Wireless Communications: A Review of Recent Advances

This paper investigates the characteristics of the active and reactive power sharing in a parallel inverters system under different system impedance conditions. The analyses conclude that the conventional droop method cannot achieve efficient power sharing for the case of a system with complex impedance condition. To achieve the proper power balance and minimize the circulating current in the different impedance situations, a novel droop controller that considers the impact of complex impedance is proposed in this paper. This controller can simplify the coupled active and reactive power relationships, which are caused by the complex impedance in the parallel system. In addition, a virtual complex impedance loop is included in the proposed controller to minimize the fundamental and harmonic circulating current that flows in the parallel system. Compared to the other methods, the proposed controller can achieve accurate power sharing, offers efficient dynamic performance, and is more adaptive to different line impedance situations. Simulation and experimental results are presented to prove the validity and the improvements achieved by the proposed controller.

Design and Analysis of the Droop Control Method for Parallel Inverters Considering the Impact of the Complex Impedance on the Power Sharing

This paper addresses the harmonic stability caused by the interactions among the wideband control of power converters and passive components in an ac power-electronics-based power system. The impedance-based analytical approach is employed and expanded to a meshed and balanced three-phase network which is dominated by multiple current- and voltage-controlled inverters with LCL- and LC-filters. A method of deriving the impedance ratios for the different inverters is proposed by means of the nodal admittance matrix. Thus, the contribution of each inverter to the harmonic stability of the power system can be readily predicted through Nyquist diagrams. Time-domain simulations and experimental tests on a three-inverter-based power system are presented. The results validate the effectiveness of the theoretical approach.

/pdf/modeling-and-analysis-of-harmonic-stability-in-an-ac-power-4k69dmcqhc.pdf

Modeling and Analysis of Harmonic Stability in an AC Power-Electronics-Based Power System

This paper discusses the steady-state operation of phase-shift modulated dual-bridge series resonant converter (DBSRC) intended for dc/dc power bidirectional control over a wide range of input and output voltages. The analysis, developed here for the most general case of three independent phase-shift control angles, demonstrates the existence of minimum current trajectories in the 3-D control space along which the DBSRC cell can deliver any admissible power level with minimum tank circulating current. At nonunity conversion ratios, minimum current operation prevents the DBSRC output bridge from experiencing severe hard-switching losses, substantially reducing the effort normally required by auxiliary zero-voltage switching assistance circuitry, and outperforming the efficiency of conventional one-angle modulation approaches especially at light load. The developed approach is validated via computer simulations and experimental tests on a 1-kW DBSRC prototype. Tests performed at a nonunity voltage conversion ratio indicate a marked light-load efficiency improvement with respect to the conventional one-angle modulation, confirming the importance of the minimum current operation when the converter is expected to operate with programmable output voltages or under wide input voltage variations.

Minimum Current Operation of Bidirectional Dual-Bridge Series Resonant DC/DC Converters

/pdf/digital-control-of-high-frequency-switched-mode-power-593n38a1r5.pdf

Digital control of high-frequency switched-mode power converters

This paper investigates multi sampled digitally controlled switched-mode power supplies with switching ripple compensation. In digital controllers for power converters, the main bandwidth limitations come from A/D conversion time, computational delays, and small-signal delay of the digital pulsewidth modulator (DPWM). In hard-wired digital-controller technologies, such as in dedicated digital IC and/or in field-programmable gate arrays (FPGAs), the calculation delays can be made negligible with respect to the switching period; thus, when fast ADCs are used, the overall phase lag is dominated by the DPWM. The multi sampling approach can strongly reduce the DPWM delay, thus breaking the bandwidth limitations of conventional single-sampled solutions. In this paper, the additional aliasing effects, which would require a filtering action, are avoided, exploiting the periodic nature of the switching ripple under steady-state conditions using a repetitive-based filtering action. Simulation and experimental results on a 1.2-V-10-A 500-kHz synchronous buck converter, where the digital control has been implemented in the FPGA, confirm the properties of the proposed solution.

High-Bandwidth Multisampled Digitally Controlled DC–DC Converters Using Ripple Compensation

This paper presents steady-state and small-signal models for digital pulsewidth modulators (DPWM) employed in multiple sampling digital control schemes for dc-dc switched mode power supplies (SMPS), and identifies the triangular modulation as intrinsically superior to other modulation schemes in multisampling applications. In conventional digital control of dc-dc converters, closed-loop bandwidth limitations are mainly set by analog-to-digital conversion times, computational delays and DPWM delays originated by the sampled nature of the PWM. While the use of hardwired logic and fast A/D converters minimizes computational and A/D delays, the DPWM small-signal phase lag strictly depends on the adopted sampling strategy. Multiple sampling techniques recently proposed in literature can achieve a strong reduction of the DPWM delay by operating the control and modulation steps at a sampling frequency strictly higher than the converter switching frequency. On the other hand, multisampled pulse width modulators (MSPWMs) exhibit nonlinear behaviors which do not have analog counterparts nor are encountered in conventional digital control, the most relevant effect being the onset of sampling induced dead bands, i.e., regions of zero modulation gain in the modulator transcharacteristic which may compromise proper closed-loop operation of the converter. The models proposed in this paper fully characterize the steady-state and small-signal behavior of DPWMs operated in multiple-sampling fashion. Multisampled triangular modulators are proven to be intrinsically superior to trailing edge or leading edge modulators in terms of linearity. Simulation and experimental results validate the proposed models and confirm the properties of triangular modulations.

Modeling of Multisampled Pulse Width Modulators for Digitally Controlled DC–DC Converters

This paper investigates the multi-sampling techniques applied to the current control in active power filter applications. In active power filter applications with digital control, the main bandwidth limitation derives from A/D conversion time, calculation delays and the sample-and-hold effect for the Digital-Pulse-Width Modulation (DPWM). Using Field Programmable Gate Arrays (FPGAs) and fast A/D converters for the control implementation, it is possible to make the former two negligible with respect to the switching period. Thus, the overall phase lag is dominated by the DPWM, which can be strongly reduced by multiple sampling approach, thus breaking bandwidth limitation of single- sampled solutions. Moreover, as the multi-sampling approach triggers nonlinear behaviors that can negatively impact the filter compensating capabilities, a solution is proposed, based on a simple digital filter, that linearizes the system behavior and does not waste the multi-sampling phase boost property. Simulation and experimental results on a 10 kVA prototype confirm the theoretical expectations.

Luca Corradini

Papers

Minimum Current Operation of Bidirectional Dual-Bridge Series Resonant DC/DC Converters

Digital control of high-frequency switched-mode power converters

High-Bandwidth Multisampled Digitally Controlled DC–DC Converters Using Ripple Compensation

Modeling of Multisampled Pulse Width Modulators for Digitally Controlled DC–DC Converters

Analysis of Multi-Sampled Current Control for Active Filters