29-05-2012, 03:00 PM
Predictive Control for Single Phase Voltage Fed Power Factor Correction Converters
Predictive Control for Single Phase.pdf (Size: 274.84 KB / Downloads: 32)
INTRODUCTION
In most power electronic applications, the power input is of 50 or 60 hertz AC voltage
provided by the electric utility. It further converted to a DC voltage for various
applications. The inexpensive rectifiers with diodes convert AC to DC and the output
voltage is uncontrolled. The controlled rectifiers are used for providing variable/ constant
output voltage. The dc output voltage of a controlled/uncontrolled rectifier should be
ripple free. Therefore a large capacitor is connected as a filter on dc side. Due to this,
controlled/uncontrolled rectifier has the following drawbacks; these rectifiers draw highly
distorted current from the Utility and Power factor is very low. To take the edge off these
drawbacks, High performance rectifiers are proposed in this paper.
One of the authors has proposed a digital controller-based predictive instantaneous
current control scheme for the single-phase voltage-fed rectifier and its modified
analogue version. Although the control schemes obtain a sufficient performance, further
simplification is necessary to realize an economical PFC converter system in practice. In
this paper propose a simplified analogue controller-based predictive instantaneous current
control scheme for single-phase voltage fed PFC converters, which is obtained from
further modification of the original digital scheme. Since three phase converters have
phase interference, a particular arrangement of the controller modulator for the threephase
system is employed to avoid such phase interference.
CONFIGURATIONS
A. Classification of different Topology
Improved power quality converters are classified on the basis of topology and type of
converter used. The topology-based classification is categorized on the basis of boost,
buck, buck–boost, multilevel, unidirectional and bidirectional voltage, current, and power
flow. The converter type can be step-up and step-down choppers, voltage source and
current-source inverters, bridge structure, etc. These converters are developed in such
vastly varying configurations to fulfill the very close and exact requirement in variety of
applications. Some of these improved Power quality converters are improved to provide
better performance from primitive configurations.
B. Current Control Techniques for PFC converters
The current control techniques have gained importance in ac to dc converters used for
high performance applications. Where the fast response and high accuracy are important.
Various current control methods have been proposed and classified as hysteresis control,
predictive control and linear control.
C. System Configuration
The topology of Boost converter is shown in Fig.1. The proposed predictive
control PFC algorithm is derived based on the following assumptions:
(a) Boost converter operates at continuous conduction mode
(b) The switching frequency is much higher than the line frequency. So the input
voltage Vin can be assumed as a constant during one switching cycle.
Figure 1. Shows the configuration of such converter to improve the power quality at ac
mains and dc output, reduced losses and noise, enhanced compactness by drastically
cutting their weight and volume. In principle, it is a combination of diode bridge rectifier
and step-up dc chopper with filtering and energy storage elements. High-frequency PWM
and predictive control techniques are used in the closed-loop controllers in outer voltagefed
loop of these converters to provide fast response and high level of power quality at
input ac mains and dc output.
Mathematical Modeling of PFC Converter
The proposed PFC Converter system comprise single-phase ac supply, power converter
circuit, and control scheme. In this section modeling equation of various components of
the converter system are formulated separately to develop a comprehensive model for
their performance simulation. Under normal operating conditions the supply system can
be modeled as a sinusoidal voltage source of amplitude Vm and frequency. The
instantaneous voltage is given as:
Determination of the objective function
The significant subject of the predictive control PFC method is how to determine the
objective function when the predictive control algorithm is implemented. In this paper,
Total Harmonic Distortion (THD) of the input current is chosen as the objective function.
The objective of the predictive control PFC algorithm is to achieve a high power factor.
The ideal situation is unity power factor.