Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
Single-phase transformerless inverters are broadly studied in literature for residential-scale\nPV applications due to their great advantages in reducing system weight, cost and elevating\nsystem efficiency. The design of transformerless inverters is based on the galvanic isolation\nmethod to eliminate the generation of leakage current. Unfortunately, the use of the galvanic\nisolation method alone cannot achieve constant common mode voltage (CMV). Therefore, a complete\nelimination of leakage current cannot be achieved. In addition, modulation techniques of single-phase\ntransformerless inverters are designed for the application of the unity power factor. Indeed,\nnext-generation PV systems are required to support reactive power to enable connectivity to the\nutility grid. In this paper, a proposed single-phase transformerless inverter is modified with the\nclamping method to achieve constant CMV during all inverter operating modes. Furthermore,\nthe modulation technique is modified by creating a new current path in the negative power region.\nAs a result, a bidirectional current path is created in the negative power region to achieve reactive\npower generation. The simulation results show that the CMV is completely clamped at half the DC\nlink voltage and the leakage current is almost completely eliminated. Furthermore, a reactive power\ngeneration is achieved with the modified modulation techniques. Additionally, the total harmonic\ndistortion (THD) of the grid current with the conventional and a modified modulation technique is\nanalyzed. The efficiency of the system is enhanced by using wide-bandgap (WBG) switching devices\nsuch as SiC MOSFET. It is observed that the efficiency of the system decreased with reactive power\ngeneration due to the bidirectional current path, which leads to increasing conduction losses....
Electrical treeing (ET) can irreversibly deteriorate the insulation of polymeric power cables\nleading to a complete failure. This paper presents the results of an experimental investigation into\nthe effects of unipolar and polarity reversing DC voltages on electrical tree (ET) and partial discharge\n(PD) behavior within high voltage direct current (HVDC) cross linked polyethylene (XLPE) cable\ninsulation. A double needle configuration was adopted to produce non-uniform electric fields\nwithin the insulation samples, potentially leading to electrical trees. The development of trees was\nmonitored through an optical method and the associated partial discharge signals were measured\nthrough an electrical detection technique, simultaneously. The analysis of the results shows reasonable\nrelation between the formation of ETs and the type of the applied voltages. The polarity reversing\nattribute of the test voltages has a pronounced effect on formation and growth of electrical trees.\nThis implicates an interaction between the space charges that accumulate within polymeric materials\nand the operational polarity reversing electric fields, which causes insulation degradation. Therefore,\nstudy of influencing HVDC operational parameters on insulation degradations can contribute to\nimprovements in cable design and advancement in insulation diagnostic strategies applicable in\nHVDC systems leading to more effective asset management....
This paper proposes a fast load transient control for a bidirectional dual-active-bridge\n(DAB) DC/DC converter. It is capable of maintaining voltageâ??time balance during a step load change\nprocess so that no overshoot current and DC offset current exist. The transient control has been\napplied for all possible transition cases and the calculation of intermediate switching angles referring\nto the fixed reference points is independent from the converter parameters and the instantaneous\ncurrent. The results have been validated by extended experimental tests....
Nowadays, most three-phase, â??off the shelfâ? inverters use electrolytic capacitors at the DC bus to provide short term energy storage.\nHowever, this has a direct impact on inverter lifetime and the total cost of the photovoltaic system. This article proposes a novel\ncontrol strategy called a 120 bus clamped PWM (120BCM). The 120BCM modulates the DC bus and uses a smaller DC bus\ncapacitor value, which is typical for film capacitors. Hence, the inverter lifetime can be increased up to the operational lifetime of\nthe photovoltaic panels.Thus, the total cost of ownership of the PV system will decrease significantly. Furthermore, the proposed\n120BCM control strategymodulates only one phase current at a time by using only one leg to perform the modulation. As a result,\nswitching losses are significantly reduced.The full system setup is designed and presented in this paper with some practical results....
The construction of an electromagnetic coupling power transfer system is introduced in\nthis paper. Considering the characteristics of the battery charger, a novel parameter design method\nbased on the load of the maximum power transfer point is proposed. Then, the compensator,\nresonant circuits, and some key parameters of the electromagnetic coupler are discussed in detail\nby constructing a mutual inductance model to carry out impedance calculation and analysis.\nCoupling coefficient influenced by different magnetic circuits and coil distribution were analyzed by\nbuilding a finite element model and an equivalent magnetic circuit. Moreover, impedance matching\nand compensation network parameters were theoretically calculated and simulated. Finally, a wireless\npower charger based on an open-loop class E amplifier with the maximum power point load\nconsideration was manufactured. Simulation and experiments were done to verify the analyses,\nand the capability of 4.2 W power delivery at a distance of 10 mm and a peak system efficiency\nexceeding 72% were demonstrated....
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