It starts at zero, reaches a peak value, and returns to zero during each switching cycle. In discontinuous inductor current mode, inductor current is zero for a portion of the switching cycle. In continuous inductor current mode, current flows continuously in the inductor during the entire switching cycle in steady-state operation. Boost Power Stage Steady-State AnalysisĪ power stage can operate in continuous or discontinuous inductor current mode. The steady state analysis for continuous conduction and discontinuous conduction mode of operation is explained below.Ī. When the switch is off, the output stage receives energy from the inductor as well as from the input. The input supplies energy to the inductor. When the switch is on, the diode is reversed biased, thus isolating the output stage. The power circuit of dc-dc Boost rectifier is shown in fig.1. The output capacitor supplies the entire load current for the rest of the switching cycle. The output current for a boost power stage is discontinuous, or pulsating, because the output diode conducts only during a portion of the switching cycle. The input current for a boost power stage is continuous, or non-pulsating, because the input current is the same as the inductor current. Power supply designers choose the boost power stage because the required output voltage is always higher than the input voltage, is the same polarity, and is not isolated from the input. The boost is a popular non-isolated power stage topology, sometimes called a step-up power stage. The steady-state stability condition and the low-frequency small-signal model of the PSM switched boost rectifier are derived by applying standard graphical and analytical methods of the current mode control. The PSM modulator has the structure of a standard current programmed controller with compensated ramp that is nonlinear. The advantage of the PSM is the extended range of Continuous Conduction Mode (CCM) of operation compared to the NLC. The input current waveform gets distorted in the Discontinuous Conduction Mode(DCM) operation of the NLC controlled boost rectifier. This enables us to predict the current ripple of the subsequent off period during the on time of the switch itself. The estimation of the inductor current is possible since the input voltage is practically constant over a switching period. In this strategy the duty ratio of the switch is controlled in such a way that the estimated inductor current will be proportional to the rectifier input voltage at the end of the switching period(Ts).
In this Paper, the Predictive Switching Modulator(PSM) for current mode control of high power factor boost rectifier is proposed. Rectifier,power factor conduction mode,Modulator Boost regulators are draws power from utility at unity power factor when it is operated in continuous conduction mode. So maintaining the output voltage with in the regulation is very complex. The main problem in boost rectifier is, the output voltage is very sensitive to Duty ratio variations. Boost regulators have been with us for many years as a power factor correction rectifiers. This fact and the presence of standards or recommendations have forced to use power factor correction in power supplies. These harmonics distort the local voltage waveform, potentially interfering with other electrical equipment connected to the same electrical service and reduce the capability of the line to provide energy. These Harmonic currents flowing through the impedances in the electrical utility distribution system can cause several problems such as voltage distortion, heating, noises. Conventional AC/DC power converters that are connected to the line through full-wave rectifier draws a non-sinusoidal input current.
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