Boost Rectifier

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  • Topic: Alternating current, Control theory, Switched-mode power supply
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International Conference On Industrial Engineering and Manufacturing ICIEM’10, May, 9-10, 2010, Batna, Algeria

SINGLE-PHASE BOOST POWER FACTOR CORRECTOR
L. RAHMANI
Laboratoire d’Automatique de Sétif (LAS), Université de Sétif, Faculté des Sciences de L’ingénieur, Département d’électrotechnique, Route de Bejaia, Sétif, Algérie, Lazhar_rah@yahoo.fr

Abstract--This paper presents the analysis, a modeling approach to obtain a small-signal model, design and the digital implementation of a linear control technique for single-phase boost power factor correctors (PFC). Such converters present nonlinear characteristics and an approximation of them are used to drive the models. The most important result obtained is that the small-signal output is not equal to the load impedance. The proposed circuit significantly improves the dynamic response of the converter to load steps without the need of a high crossover frequency of the voltage loop by adding low-pass filter, so that a low distortion of the input current is easily achieved. This controller has been verified via simulation in Simulink using a continuous time plant model and a discrete time controller. Index Terms—power, factor, correction, boost, rectifier.

I. INTRODUCTION. Single-phase power factor correction (PFC) circuits provide rectification of the line voltage to a regulated dc voltage while shaping the input current to be a sinusoid and in phase with the line voltage [1]. Often, the PFC acts as a preregulator to a dc–dc converter that may be used to provide additional regulation and ohmic isolation [2], [3]. Due to adoption of IEC 1000-3-2 [4] as the EN61000-3-2 norm in Europe and the formulation of the IEEE 519 [5] in the USA, these circuits are increasingly being used in the front-end of electronic equipment. Among the several possible topologies [2], the boost PFC shown in Fig. 1 is most commonly used. The control objectives are to track the inductor current to a rectified Sinusoid (so that the line current is sinusoidal and in phase with the line voltage) and to regulate the average output voltage to a desired magnitude and to has a fast response to the load variation [6], [7]. Commonly, a linear controller is designed utilizing a small-signal model that is obtained by linearization about an operating point [6]. The system provides acceptable performance. However, the controller has an inherent drawback of third harmonic in the input current. This happens because the reference current signal is the product of an output voltage error amplifier (that contains a second-harmonic component) and the input voltage wave shape. Thus, the voltage loop gain at 100 Hz effectively determines the level of third harmonic to be expected in the input voltage [8]. Several commercial ICs incorporate the required analog components to implement the linear control scheme. Recently, there has been a

significant interest in an all-digital implementation, available for the PFC application, digital implementation of the linear control design using commercial microcontrollers and DSPs has been carried out. Since the computation time of commercial low-cost microcontroller is significantly high, a discrete version of the conventional analog design cannot be directly implemented without significant modification to the design of the voltage control loop. To improve the dynamic response of the converter to load steps, the 100 Hz notch filter is inserted to the voltage control loop. The notch filter reduces the amount of second harmonic (to cancel the output voltage ripple) that is reaching the multiplier. Thus, the voltage loop bandwidth can be increased, which leads to a faster transient response, without the penalty of increased third harmonic in steady state. For faster dynamic response, current mode control is adopted instead of voltage mode control. Both peak current mode and average current mode controls are widely used [9]. The main deference between the two methods is that, in...
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