Multiple-input dc-dc converters to enhance local availability in grids using distributed generation resources

This paper studies boundary control for a multiple-input buck-boost (MIBB) converter topology with equal voltages at each input leg. In addition to not requiring different input voltages as in previously suggested MIBB converters, when input voltages are equal the proposed controller eliminate the need for forward-conducting bidirectional-blocking switches (FCBBs) also present in previous MIBB topologies. The prescribed controller makes the closed loop MIBB system to behave as a single-input buck-boost converter so that a solution to in the sense of Filippov can be defined in reflective mode. Large-signal asymptotic stability of the desired operating point is subsequently established using Lyapunov's direct method. The state-dependent switching strategy presented ensures that the system avoids certain limitations that occur when multiple-input converters that operate based on switching period-sharing. These restrictions include different input voltages, and limited number of input legs. A lower parts count and better efficiency may then be achieved. Robustness and other attributes of boundary control make the proposed strategy favorable. Both pros and cons of the proposed scheme are discussed and design recommendations are given. The analysis is verified by simulations and an experimental setup with four input legs.

This paper explores the feasibility of active clamping techniques in isolated time-sharing multiple-input converters. Additional losses caused by energy transfer into the input switches from the leakage inductance in the isolating coupled-inductor are addressed with a common active clamping leg for all input legs. An active clamping technique is applied to isolated time-sharing multiple-input converters to minimize the additional switching losses, and the paper also conducts an operational analysis of a dual-input isolated single ended primary inductor converter (2IISEPIC) with the active clamping technique. Zero-voltage-switching can be achieved on the first-turned-on input leg and the active clamping leg with proper driving strategy and circuit parameter settings. Discussions on the effect of the active clamping technique to a multiple-input converter and the components stresses of the 2IISEPIC with the active clamping technique have also been made to assist in the design of time-sharing multiple-input converters. A prototype of the 2IISEPIC with the active clamping technique is built for efficiency and stresses verification, and it is showed that 94% efficiency is achievable at 200W output power and the component stresses are significantly reduced, especially the voltage stresses on input switches. An absolute 6 % improvement over the efficiency of the same circuit without soft-switching techniques is observed.

As compared with parallel converters employing buck converters or boost converters, the analysis of multiple-input parallel switched-capacitor (SC) DC-DC converters is not sufficient. In this paper, a multiple-input parallel DC-DC converter designed by using SC techniques is proposed for mobile back-lighting applications, and handy theoretical formulas are given concerning the power efficiency and equivalent circuit. The proposed parallel converter consists of two different kinds of converter blocks: 1. a 1.5× step-up SC DC-DC converter employing an input voltage from a lithium battery and 2. a novel step-up converter employing an input voltage from solar cells. The proposed converter can offer the output voltage for display back-lighting from solar energy, because the proposed step-up converter can achieve not only a large step-up conversion ratio but also a wide input range. Hence, the proposed converter will enable us to realize a long battery life, reduction of heat, and so on. Furthermore, derived theoretical formulas will be helpful to estimate circuit characteristics, because theoretical results agree well with SPICE simulation results. The validity of circuit design is confirmed by simulations and experiments.

Distributed generation models have started to be seen intensively in distribution networks with technological developments. The increase in distributed generation resources has brought changes in the grid. Problems such as improper operation of grid protection systems and imbalances in load flow have emerged. In this article, short circuit and load flow analyses of a low voltage distribution network with a distributed generation source are performed and the effects on the network are predicted. Results and predictions regarding the optimum operating conditions of distribution networks in the presence of distributed generation resources have been obtained. Real-time analyses are performed with a power quality measurement device. Scenarios are created in different situations in the presence of distributed generation resources. These scenarios are analysed using a network simulation program. The simulation programme analysed the effects of seasonal conditions and changes in power generation and loads on distribution transformers. In the light of the data obtained, the changes that are required to be made in the inventories in the network topology considering the changes in energy generation time and voltage levels outside the energy generation time are specified. Applications such as automatic tap switching of distribution transformers after a certain power level are proposed.

This paper studies a multiple-input dc-dc converter realized from a standard single ended primary inductor converter topology. The proposed configuration allows the integration of different distributed generation sources into a common DC main bus. This work discusses the converter topology, basic dynamic equations, and explains its basic operation. Stability characteristics are also explored with linear methods. Theoretical analyses are verified with simulations and experimental results.

This paper presents the design and simulation of Multiple-Input Single-Output (MISO) dc-dc converter. The main purpose of the converter is to allow connection of multiple power sources to a single dc bus system. Design and modeling of the MISO converter will first be discussed. Results of the computer simulation will be presented which demonstrate the ability of the converter to accept multiple dc sources while outputting only one dc voltage.

DC power packet dispatching system is reported recently aiming to deliver power in a packet form. It can utilize less power conversion stages which increases power distribution efficiency and monitor load demand intelligently from source side to keep the system stable. A multiple-energy-source mixer based on a multiple-input single-inductor buck converter for DC power packet dispatching system is proposed. It is capable of generating power packets at different voltage levels by time sharing of multiple power sources. In this work, three different sources including a PV panel and two DC voltage sources are used for the power packet dispatching system. A control strategy is devised in order that the PV panel can track maximum power point (MPP) approximately and the PV is given a priority to share power in each power packet generation. Experimental results are reported to verify the proposed mixer and its control strategy for DC power packet dispatching system.

This work introduces a new Multiple-Input Multiple-Output Modular Multilevel dc-dc Converter (MIMO- MMC). The proposed topology has a bidirectional structure and may be utilized in both low and high power applications ranging from approximately 100W to 10MW. The modular structure of the MIMO-MMC enables efficient component utilization through module voltage and current sharing capabilities. The topology can supply or extract regulated power from �� controllable voltage nodes without requiring source or load multiplexing, resulting in minimized filtering requirements. The MIMO-MMC's structure is described, and the steady state operation of the converter is theoretically analyzed. Based on the derived dynamic model of the converter, an effective control algorithm is proposed. The steady-state operation and dynamic response of the converter is investigated through both simulation and experiment.

Efficiency and power density are the two most important index of the telecom rectifier development. During recent years, the efficiency of the telecom rectifier is pushed from 92% to 96% and now 98%, this paper however explores the design considerations of super high density telecom rectifiers in concert with high efficiency requirements (96%). Specifically, the design considerations of a high switching frequency (1MHz) and high efficiency interleaving totem pole PFC stage with DCM boundary control. A high resonant frequency (1MHz), PCB winding based LLC DCDC stage is explained. The different type wide band device 650V GaN HEMT is used for PFC stage and D2D stage. Experimental results are presented to validate the design concept

Energy savings continues to build momentum on a global scale. The telecommunication industry has responded with high efficiency DC power systems to reduce energy consumption. This paper explores the design considerations of high efficiency (96%) telecom rectifiers in concert with high power density requirements (34W/inch3). Specifically, the design considerations of a high efficiency, high density bridgeless PFC stage followed by a LLC DC-to-DC stage is explained. Experimental results are presented to validate the design approach.

The Modular Multilevel Cascade Converters (MMCC) present themselves as one of the solutions for high power and high voltage applications. Modularity and low voltage stress in each semiconductor are some of the features of this solution. This paper presents a study with experimental results concerning an MMCC composed by three full-bridge submodules with a common DC-bus and with low frequency cascaded transformers. Sharing the DC bus for each submodule al-lows for a simpler control algorithm as well as a simpler interface point with renewable energy sources or energy storage systems. Along the paper, it is presented the step-by-step methodology to obtain the main parameters of the elements that constitute the MMCC, namely the transformers equivalents model. Thus, it was possible to develop a more realistic simulation model, whose results obtained are very similar to the experimental results.KeywordsModular multilevel cascade converter (MMCC)Cascade transformersSimulation model

The microgrid is a very effective way of integrating various distributed generation resources into the ac power system. To provide electric power of high reliability, the converters in the microgrid often rely on autonomous droop control methods to reduce their dependence on communication and need to operate in both the islanded mode and the grid-connected mode. In this paper, a grid synchronization method for a multiconverter distributed generation system is proposed. The proposed grid synchronization method allows multiple droop-controlled converters to adjust the frequency, phase, and amplitude of their output voltages to prepare for grid connection. The entire synchronization process can be executed with very limited communication requirement. This paper provides detailed explanation on the proposed grid synchronization method. Experimental test results are presented to validate the effectiveness of the proposed method.

Reconfigurable solar photovoltaic systems: A review

From economical aspects, the multidrive systems are a promising application area for the converters, where the cost and size of the converters are shared by multiple inverter-motors. Given terminal constraints of unity power factor in grid line and independent multiple motor controls in output ports, two multidrive topologies are possible: one with single PWM-VSR feeding inverters through the common dc bus, and the other using a diode rectifier and an active power filter with its own load. Despite several publications for two systems, the features and advantages of the two systems have not been clearly explained. This paper, in detail, presents the theoretical analyses and systematic comparisons of the two multidrive topologies, from converter kilovolt-ampere ratings, dc-link voltage requirements, switch ratings, semiconductor losses, and reactive component designs point of views.

The parallel three-phase grid-connected converters (GCCs) with common dc and ac buses can increase the system power level effectively. However, zero sequence circulating current (ZSCC) will occur inevitably. In this paper, the mechanisms and characteristics of ZSCC in two parallel three-phase GCCs are first investigated based on three typical cases. From the analysis, it was found that not all ZSCC can be suppressed. Generally speaking, ZSCC caused by inconsistent modulation voltages between modules cannot be effectively handled. And ZSCC caused by different injected zero sequence voltages (ZSVs) or asynchronous carriers can be suppressed. Based on the theoretical analysis, identical ZSV injection and carrier synchronization methods without communication are, thus, proposed to suppress ZSCC at the source, which are easily implemented without adding any hardware. Finally, the theoretical analysis and the effectiveness of the proposed methods on ZSCC suppression are well-verified by experiments.