An analysis of the power factor as a function of these dead times can be found in 1617. In the case of sinusoidal line voltage this means that the converter must draw a sinusoidal current from the utility in order to do that a suitable sinusoidal reference is generally needed and the control objective is to force the input current to follow as close as possible this current reference. . In particular the energy stored in the inductor is given by: So the inductor current has to be the same at the start and end of the commutation cycle. The boost power factor correction converter is one circuit that can be added to power supplies to significantly improve their power quality. The same is true for the output diode. To ensure that electronic devices do not have a significant cumulative effect on the power factor of the grid, international standards such as and set limits on the power-factor degradation and harmonic distortion introduced by power supplies.
Furthermore in discontinuous operation the output voltage gain not only depends on the duty cycle but also on the inductor value the input voltage the switching frequency and the output current. The first state occurs when S 1 is closed, as shown in Figure 2. Filters made of capacitors sometimes in combination with inductors are normally added to the output of the converter to reduce output voltage ripple. A showed that simple passive filters are not enough to adequately improve the power factor or harmonic distortion. That said, proposes a 2-stage Boost-Buck converter topology as opposed to one-stage Boost-Buck , in order to control input current with the first stage and to reduce output voltage with the last one Which could not be done with a Boost converter alone. T for his guidance encouragement and for all facilities to complete this project. The switch must have a current rating at least equal to the maximum peak current in the inductor and a voltage rating at least equal to the output voltage.
The second harmonic content of the rectified line voltage is 66. Since they are completely disconnecting from power source while switching, input current is inherently discontinuous which is not desired if we are attempting to control it. Thus the voltage across the inductor and the input voltage are in series and together charge the output capacitor to a voltage higher than the input voltage. Linear loads with low power factor induction motor can be corrected with a passive network of capacitors or inductors. In a boost converter the output voltage is always higher than the input voltage. The switching frequency must be high enough to make the power circuits small and minimize the distortion and must be low enough to keep the efficiency high. Converters operating at higher power levels may find that a lower switching frequency is desirable to minimize the power losses.
Even more challenging is the fact that these power supplies are non-linear loads, so the power factor cannot be corrected by simply adding reactive components i. Distortion power factor is a measure of how much the harmonic distortion of a load current decreases the average power transferred to the load. Thus, by varying the duty cycle, the average inductor current can be adjusted. T for her guidance throughout this project. The boost topology is very simple and allows low-distorted input currents and almost unity power factor with different control techniques. Because of the costs of larger equipment and wasted energy electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor.
The concept can be generalized to a total distortion or true power factor where the apparent power includes all harmonic components. This latter is obtained in the same way as in the peak current control. Turn-on snubbers for the switch will reduce the switching losses and can be very effective in allowing a converter to operate at high switching frequency with very high efficiency. Converter topologies such as Buck Shown in next image and Flyback work by quickly connecting and disconnecting themselves from supply source in order to modify their output voltage while keeping it continuous with stored energy from capacitors and inductors. To learn more, see our. Typical values for C o are1µF to 2µF per watt. This is why this converter is sometimes referred to as a step-up converter.
The cycling between the two states is done at a high frequency that is at least in the tens of kHz, but is often an order of magnitude or even more higher than that. I also express my sincere thanks to Prof. From this point of view the standard rectifier employing a diode bridge followed by a filter capacitor gives unacceptable performances. This means the overall change in the current the sum of the changes is zero: Substituting and by their expressions yields: This can be written as: This in turn reveals the duty cycle to be: 13 slide 14: From the above expression it can be seen that the output voltage is always higher than the input voltage as the duty cycle goes from 0 to 1 and that it increases with D theoretically to infinity as D approaches 1. There is a more recent version of your browser available. The large electrolytic capacitors which are normally chosen for the output capacitor have an equivalent series resistance which changes with frequency and is generally high at low frequencies.
Professor department of Electrical Engineering and G. It represents the fraction of the commutation period T during which the switch is On. Kanchandani 3 Sangsun Kim Prasad N. For the example circuit the diode is a high speed, high voltage type with 35ns reverse recovery, 600Vdc breakdown, and 8A forward current ratings. If we consider zero voltage drop in the diode and a capacitor large enough for its voltage to remain constant the evolution of I L is: Therefore the variation of I L during the Off-period is: As we consider that the converter operates in steady-state conditions the amount of energy stored in each of its components has to be the same at the beginning and at the end of a commutation cycle.
Active solutions are the most popular way to meet the legislation requirements. The value of the inductor will be reasonably small and cusp distortion will be minimized, the inductor will be physically small and the loss due to the output diode will not be excessive. The output voltage can be calculated as follows in the case of an ideal converter i. Various control strategies have also been implemented. The diode in the example circuit was chosen for its fast turn off and the switch was oversized to handle the high peak power dissipation.