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ABSTRACT: In traditional neutral-point-clamped (NPC) inverters, two major operating issues encountered are their relatively limited voltage-buck variation range and capacitive-voltage imbalance, which can cause low-order harmonics to appear at the inverter output. Various methodologies have so far been introduced for extending the inverters' variation range to include voltage-boost operation, but they generally require the inclusion of large passive components or have not yet been optimized in terms of waveform quality. The balancing of their capacitive voltages using a simple technique has also not yet been investigated in the context of buck-boost energy conversion, even though relevant techniques for traditional NPC inverters do exist but are generally overburdened by the accompanied switching loss increase and more complex control and hardware circuitries. To address these two topological concerns simultaneously, two new buck-boost NPC inverters with simple capacitive-voltage-balancing capability are proposed. Both inverters are demonstrated to exhibit a doubling of voltage gain, with one of them also shown to produce a better output waveform quality. Simulation and experimental results are provided for verifying the viability and practicality of the proposed inverters.
IEEE Transactions on Industry Applications 07/2010; · 1.66 Impact Factor
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ABSTRACT: To date, many inverter topologies have been proposed in the literature with each exhibiting certain advantages and disadvantages. These inverters are however mostly proposed with their reliability indexes left unexplored. The main reason for a lack of reliability assessment might be a lack of existing quantitative techniques that can be used for computing a mathematical index for associating with the inverter topology under consideration. Without the relevant mathematical index, comparing of inverter reliability is generally impossible or merely based on qualitative reasoning, which at times is subjective to individual preferences. Aiming to address that issue on reliability assessment, this paper proposes an appropriate method based on multi-state computation, uniquely fine-tuned for inverter (or general converter) evaluation. To demonstrate its applications, the formulated method is indifferently used for computing the reliability indexes / models of existing single-phase and three-phase three-level inverters to provide a common ground for their reliability evaluation. For inverters with possibilities of raising their indexes, topological and modulation modifications are proposed with their practicality and performance verified in simulation and experimentally.
Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE; 03/2010
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ABSTRACT: This paper presents a new approach of maximizing energy harvesting in photovoltaic (PV) systems using bisection search theorem (BST). The fundamental of the BST and its application into maximum power point tracker (MPPT) in PV systems are described. A microcontroller is used to control a DC/DC boost converter to realize the MPPT function. Experimental results from solar array simulator show that the proposed technique can track maximum power point very fast within a few steps. The feasibility of the proposed MPPT is also verified in natural environment condition with two solar modules in parallel. Since the proposed technique is simple in computation, cheap in implementation and fast in tracking, it is expected to be widely used to replace conventional MPPT techniques in PV systems.
Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE; 03/2010
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ABSTRACT: Hybrid-source impedance networks have attracted attention among researchers because of their flexibility in performing buck-boost energy conversion. To date, three distinct types of impedance networks can be summarized for implementing voltage-type inverters, with another three types summarized for current-type inverters. These impedance networks can in principle be combined into a single generic network entity, before generalized cascading concepts are proposed for connecting multiple of them together to form energy converters with a higher output voltage gain and other unique advantages. It is anticipated that these concepts and their formed inverters can find applications in photovoltaic and other renewable systems, which in turn motivate the investigation initiated here on two-level and three-level generalized cascading concepts. In addition to their theoretical performance merits, practical shortcomings and relevant transient phenomena exhibited by the generalized concepts are discussed to provide a comprehensive knowledge base needed for weighing relevant tradeoffs before deciding on a particular application.
Power Electronics and Drive Systems, 2009. PEDS 2009. International Conference on; 12/2009
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ABSTRACT: This paper presents a new mathematical model of a solar module. Solar module temperature, solar radiation and its effect on series resistance are taken into account in the model. The experimental data of the solar module under natural environment condition have been obtained to determine the model parameters. Then, the developed model is used to simulate energy yield of the solar module. This energy yield is compared with those obtained from experimental data and conventional approach. The results indicate that the proposed approach can have more accurate energy yield than conventional approach. Thus, it can be useful for the design of PV systems.
Power Electronics and Drive Systems, 2009. PEDS 2009. International Conference on; 12/2009
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ABSTRACT: In this paper, a double-edge modulation based one-cycle-control (OCC) scheme is presented for regulation of active rectifier. With minor modifications made in OCC core, the nonlinear carrier formed by integration and reset of dc-link voltage error turns out to be a symmetrical triangle waveform in steady-state, which can effectively eliminate the even order harmonics generated by the conventional OCC in three-phase systems. To cater for high power applications, LCL-filter is subsequently introduced for switching ripple suppression. In this case, it is shown that active rectifiers controlled by the proposed OCC may exhibit significant loss reduction in passive damping mode and much lower total harmonic distortion (THD) of input currents in active damping mode. Furthermore, practical implementation issues like tuning of active damping gain and triplen offset injection in OCC are also discussed in details. All the theoretical findings discovered in this paper are eventually verified by experimental testing on a 1 kW laboratory prototype.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
