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Thursday, 16 June 2011

TORQUE CONTROL OF AN INDUCTION MACHINE FED BY A MATRIX CONVERTER WITH REACTIVE INPUT POWER CONTROL

ABSTRACT

This paper presents a new control method for a matrix-converter-based induction machine drive. A discrete model of the converter, motor, and input filter is used to predict the behaviour of torque, flux, and input power to the drive. The switching state that optimizes the value of a quality function, used as the evaluation criterion, is selected and applied during the next discrete-time interval. Experimental results confirm that the proposed strategy gives high-quality control of the torque, flux, and power factor with a fast dynamic control response. The key implementation issues are analyzed in depth to give an overview of the realization aspects of the proposed algorithm. The method has a fast torque response, unity PF with low reactive power delivered to the mains, and low torque and flux ripple. The objectives of this paper are to introduce the method and its theoretical background, analyzing, in depth, the most relevant issues related to its implementation and showing its excellent performance based on experimental results.

ELIMINATION OF THE OUTPUT VOLTAGE IMBALANCE IN A HALF - BRIDGE BOOST RECTIFIER

ABSTRACT

The applications of ac–dc rectifiers are prerequisite nowadays in the power electronics industry. Due to tougher regulations on the input current harmonics, many topologies of the switch-mode boost-type power factor corrector (PFC) circuits have been presented in recent years. In this paper, a four-switch voltage-doubler boost rectifier is analyzed. A new control scheme is proposed to eliminate the output voltage imbalance when the load is unevenly distributed across the two output dc rails. Unipolar pulse width modulation switching patterns are adopted to slow down the discharging rate of the output capacitor with the lower voltage. No dc or out-of phase component is injected in the source current. Thus, the unity input power factor can be genuinely achieved. Two hysteresis comparators are employed in the presented controller. One is used for the source current to track its command. The other comparator is to confine the output voltage imbalance within a reasonable level. Modified averaged circuit models are adopted to derive the limits of the ratio of the dual loads for output voltage balance. Experimental results on prototype circuits confirm tightly with the theoretical analysis.

A HIGH-POWER-FACTOR SINGLE-STAGE SINGLE SWITCH ELECTRONIC BALLAST FOR COMPACT

COMPACT fluorescent lamps (CFLs) were first introduced in the early 1990s, and are now gradually replacing conventional incandescent lamps in household and commercial lighting. The reason for the CFL’s increasing popularity is that it conserves energy, and subsequently, reduces energy cost when compared to traditional incandescent lamps. Fig. 1 shows the power consumption comparison between CFLs and different types of incandescent lamps. From Fig. 1, it is clear that in order to produce the same amount of light output, CFLs only consumes one-third of the power an incandescent lamp requires and that the CFL’s lifetime is thousand times that of an incandescent lamp [1]. The major difference between fluorescent lamps and incandescent lamps is that fluorescent lamps have negative resistance characteristics, which means that as the fluorescent lamp power increases, the lamp current increases with a decrease in the lamp voltage .

As a result, fluorescent lamps cannot be connected directly to the line, as in the case of incandescent lamps. A lamp current stabilization element called ballast is required in order to provide sufficient voltage for proper lamp ignition and to stabilize the lamp current once the lamp arc is established. To provide a compact and lightweight solution for CFLs, high-frequency electronic ballasts operating at higher frequency than 25 kHz are more suitable than magnetic ballasts. By operating at a higher frequency, the light efficacy can be increased by at least 20% and advanced dimming control can also be implemented with great flexibility. To minimize cost and to ensure that a compact electronic ballast circuit can be installed at the base of a CFL, commercial CFLs normally do not include a power factor correction (PFC) circuit in their electronic ballasts. Fig. 2 is a block diagram of typical electronic ballast used in a commercial CFL. It consists of a diode rectifier and a self-driven half-bridge parallel resonant inverter [2] & [3] with a dc-link capacitor connected in between to provide the required energy to the lamp. The major drawback of this type of circuit configuration is the highly distorted line current drawn at the input. The poor quality of the line current, when reflected back to the utility side, produces a large amount of unwanted harmonics and results in very poor power factor. Although, it has been reported in [4] that the high total harmonic distortion (THD) issue in the line current causes only little concern for the power quality when the CFLs are less than 25% of a building’s total load, this will become a more severe problem

A SINGLE STAGE HIGH POWER FACTOR AC/DC CONVERTER

ABSTRACT

Nowadays the ac/dc converters are widely used in many off-line power supplies. The increasing amount urges researchers to develop more efficient, smaller size, and low cost ac/dc converters. Traditionally, an ac/dc converter consists of a diode-bridge rectifier followed by a bulky capacitor and a high-frequency dc/dc converter. This kind of converter inevitably introduces highly distorted input current, resulting in a large amount of harmonics and a low power factor. paper proposes a single-stage high-power-factor ac/dc converter with symmetrical topology. The circuit topology is derived from the integration of two buck-boost power-factor-correction (PFC) converters and a full-bridge series-resonant dc/dc converter. Switch-utilization factor is improved by using two active switches to serve in the PFC circuits. A high power factor at the input line is assured by operating the buck-boost converters at discontinuous conduction mode. With symmetrical operation and elaborately designed circuit parameters, zero-voltage-switching on all the active power switches of the converter can be retained to achieve high circuit efficiency. The operation modes and design equations for the circuit parameters are proposed.

A NEW MPPT METHOD FOR LOW POWER SOLAR ENERGY HARVESTING

ABSTRACT

This paper describes a new maximum-power-point tracking (MPPT) method focused on low-power (< 1 W) photovoltaic (PV) panels. The static and dynamic performance is theoretically analyzed. In order to extract the maximum power from a photovoltaic (PV) panel, several maximum-power-point-tracking (MPPT) methods have been proposed and used for high-power systems .Their application to low-power PV panels (< 1 W) has just recently been proposed and poses new challenges to achieve a net power gain. In contrast to high-power applications, the power consumption of the MPPT control circuit can contribute significantly to the final power efficiency. This paper proposes and implements a new MPPT method that is particularly suitable for these low-power source levels. The method does not require complex operations and can be implemented with low-power components. This method is feasible due to the low power consumption of the MPPT controller.

INTEGRATED INVERTER FOR BUILDING INTEGRATED PHOTOVOLTAICS

abstract

With the cost of the conventional sources of energy such as oil and gas steadily increasing, and the cost of silicon and solar cells decreasing, the conversion of solar energy to electricity is rapidly becoming an economically viable alternative, with the nature having abundance of solar power. However, the output of a solar cell is in the form of direct current (dc) power, while most appliances and other electrical devices in residential used require an alternate (ac) power normally supplied by the utility. The required conversion to match the different kinds of source and load power can be realized by dc-to-ac inverters of two different types: Stand-alone inverter and grid-connected inverter. The solar array power fluctuates considerably during each day, depending on the insolation level, weather conditions (clouds) etc. the residential load current also experiences extremely wide variations in the course of a day depending on the actual usage of various appliances in the residence. Hence a need to balance the source and load power flow is created.

Development of new technologies for low-cost manufacturing of thin-film photovoltaic (PV) power cells will enable new types of building materials that integrate photovoltaic power generating elements. In this role, the photovoltaic modules become architectural elements, requiring properties such as a low profile, ease of connection to the utility system, and the ability to maximize energy capture in a complex physical environment having shadows and reflections. In addition, the ability to generate ac simplifies connection to the ac utility system and can substantially reduce installation and other balance-of-system costs. Meeting these requirements requires low-power inverters having very low profile and high efficiency; which has led to the development of Micro-inverters.

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