Current Issue : October - December Volume : 2018 Issue Number : 4 Articles : 5 Articles
A high efficiency dcââ?¬â??dc converter is studied for light rail transportation applications on\nDC microgrid systems. The adopted structure includes two series-connected resonant circuits with\nsingle isolated transformer from input 750 V to output 48 V. Two half-bridge resonant circuits and\none voltage balance capacitor are used to reduce voltage rating of active devices and to realize split\nvoltages balance. Two series resonant circuits are connected with input-series by single transformer\nto reduce primary root-mean-square currents. Therefore, power devices with low voltage rating are\nselected in studied circuit to reduce power loss on sower devices and transformer winding of the\nisolated transformer. Frequency control approach is adopted to adjust load voltage under different\nvoltage condition and current variations. Since the equivalent resonant tank of the studied circuit\nis activated under inductive load, active devices are easily operated at zero-voltage switching over\nwide voltage and current operation range. The feasibility of the studied circuit has been verified with\na 1 kW prototype....
The increasing integration of large solar PV and wind farms into the power grid has\nfueled, over the past two decades, growing demands for high-power, high-voltage, utility-scale\ninverters. Multilevel inverters have emerged as the industry�s choice for megawatt-range inverters\nbecause of their reduced voltage stress, capability for generating an almost-sinusoidal voltage,\nbuilt-in redundancy and other benefits. This paper presents a novel switched-source multilevel\ninverter (SS MLI) architecture. This new inverter shows superior capabilities when compared\nto existing topologies. It has reduced voltage stress on the semiconductor, uses fewer switches\n(i.e., reduced size/weight/cost) and exhibits increased efficiency. The proposed SS MLI is comprised\nof two voltage sources (V1,V2) and six switches. It is capable of generating five-level output voltage\nin symmetric mode (i.e., V1 = V2) and seven-level output voltage in asymmetric mode (i.e., V1 = V2).\nWe present simulations results (using MATLAB R /Simulink R ) for five- and seven-level output\nvoltages, and they strongly support the validity of the proposed inverter. These positive results are\nfurther supported experimentally using a laboratory prototype....
The battery management system (BMS) is the key development for energy storage systems,\nand battery balancing is an important subsystem of the BMS. However, with rapid development of\nsupercapacitors, future energy storage cells are not constrained by one type, while different types of\ncells may form a source package (SP). Furthermore, the introduction of second-life batteries from\nretired electric vehicles promotes the demand of effective balancing systems for SPs with hybrid\ncells, as well as the requirement that balancing should be extended to any preset ratio rather than\n1:1. This paper proposes a novel tapped inductor balancing circuit that allows any ratio of voltage\nbalancing for hybrid energy storage cells. The analysis of the circuit, simulation and experiment\nresults are presented to demonstrate its effectiveness in handling hybrid source balancing....
Active power steady-state security regions (APSSRs), which can provide guidance for\nprevention and control through security checks, is of great importance for the safe operation of power\nsystems in which more and more sustainable energy power generation is integrated. As a mature\nflexible AC transmission system (FACTS) device, thyristor-controlled series compensators (TCSCs)\ncan carry out series compensation for the transmission line by controlling its equivalent reactance.\nWith the change of the equivalent reactance parameter of a TCSC, the nodal admittance matrix\nand power flow distribution of the power system also changes. Inevitably, the APSSR will be\ndifferent. Therefore, it is necessary and important to further incorporate the equivalent reactance\nparameters of TCSCs in the APSSR expression, which is generally established in the space of node\nactive power injections. In this paper, a rapid construction method of APSSRs incorporating the\nequivalent reactances of TCSCs is proposed. Firstly, applicability and efficiency of the conventional\nAPSSR construction method for power systems with TCSCs are analyzed. Further, with equivalent\ndisconnection of TCSC branches, the effect of TCSC equivalent reactances on the distribution of active\npower flow through changing the structure parameters is treated as modifying node active power\ninjections. On this basis, explicit expressions of APSSRs with a single TCSC equivalent reactance\nparameter and double TCSC equivalent reactance parameters are derived, respectively. Moreover,\nby deducing the general formula of APSSRs with multiple TCSC equivalent reactance parameters,\nthe feasibility of the proposed method for power systems with multiple TCSCs is analyzed. Eventually,\nvia benchmarks with different scales and a different number of TCSCs, validity and superiorities of\nthe proposed method in computational efficiency are demonstrated....
A novel rectifier based on a triple line-voltage cascaded VIENNA converter (LVC-VC)\nwas proposed. Compared to the conventional cascaded H-bridge converters, the switch voltage\nstress is lower, and the numbers of switches and dc capacitors are fewer under similar operating\nconditions in the proposed new multilevel converter. The modeling and control for the LVC-VC\nware presented. Based on the analysis of the operation principle of the new converter, the power\nfactor correction of the proposed converter was realized by employing a traditional one-cycle control\nstrategy. The minimum average value and maximum harmonic components of the dc-link voltages\nof the three VIENNA rectifier modules ware calculated. Three VIENNA dc-link voltages were\nunbalanced under the unbalanced load conditions, so the zero sequence current was injected to the\nthree inner currents for balancing three VIENNA dc-link voltages. Simulation and the results of the\nexperiment verified the availability of the new proposed multilevel converter and the effectiveness of\nthe corresponding control strategy applied....
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