Single phase controlled rectifiers pdf

Download Free PDF. Single-Phase Controlled Rectifiers. Ravi Kiran. A short summary of this paper. In the negative half- cycle, the thyristor is reverse biased and cannot switch on. The larger the delay angle, the smaller is the average load voltage. Determine the power absorbed by the resistor. Briefly describe what happen if the circuit is replaced by diode to produce the same average output.

The circuit is zero. If a keeps the SCR forward-biased till diode instead of an SCR has the energy stored in the inductor been used, the diode would becomes zero. In either case voltage across the load is Vs. Average output voltage is positive. Converter operates in the rectifying mode. Power to the load is positive 4. The tion, Fig. The load voltage is similar to The input current can be expressed as a Fourier and its waveform is shown in Fig. Finally the In effect, Eq. Equation This operating mode is called inverter or inverting mode, because the energy is transferred from the dc to the ac side.

The most important operation modes of off time. Considering Eqs. In this case the line voltage is present. During a loss of the ac main supply, If the condition of Eq. When the load demands an over- current to the inverter, the static bypass switch is turned on and the critical load is fed directly from In the circuit loads. These operating modes are Fig. This arrangement, known as a dual converter shown in Fig. This current has a harmonic content shown in Fig.

In the last several years, the massive use of single-phase power converters has increased the problems of TABLE This class of equipment must satisfy certain consequently an increase in the absolute value of the source harmonic limits, shown in Fig. It is clear that a single- current is. This standard has been the motivation for the devel- current is described by opment of active methods to improve the quality of the input current and, consequently, the power factor.

When half-wave of is in Fig. The tradeoff 1 for this improvement is an increase in the switching frequency, which is proportional to the commutation losses of the transis- tors.

As can be 0 seen, the input current presents a third-harmonic component. The enough energy to increase the current value, for this reason it total harmonic distortion of the current in Fig. The reference behavior for step changes in the load. A hysteresis controller provides a current is. The control During the on-state, shown in Fig. Hence, the inductor current iL increases at a rate proportional to the instantaneous a value of the supply voltage.

As a result, during the on-state, the iL L D iD average supply current is is proportional to the supply voltage vs which yields to power factor correction.

The instantaneous vs Filter T C Load current value decreases since the load voltage vo is higher than the supply peak voltage at a rate proportional to the difference between the supply and load voltage.

Finally, the last mode, b illustrated in Fig. The control strategy can be c implemented with analog circuitry as shown in Fig. A qualitative example of the supply voltage and current obtained using DCM is illustrated in Fig.

This reduces factor. There- sition from on- to off- state or from off- to on-state, can be fore boost-DCM applications are limited to W power reduced or even eliminated, if the switch transition occurs levels, to meet standards and regulations.

The DCM with vari- when: a the current across the power semiconductor is zero; able switching frequency reduces this harmonic content, at b the voltage between the power terminals of the power expends of a wide distributed current spectrum and all related semiconductor is zero.

This operation mode is used in the so-called resonant or soft- switched converters, which are discussed in detail in a different chapter of this handbook. Resonant operation can also be used with the boost con- In order to produce this condition, topology An important issue in power electronics is the power losses in of Fig.

ZCS [2] is shown. As can be seen, additional resonant induc- The conduction losses are produced by the current through tors Lr1 , Lr2 , capacitors Cr , diodes Dr1 , Dr2 , and power the semiconductor juncture, so these losses are unavoidable.

L Lr Dr1 The C R transistors are switched complementary to control the wave- Resonant form of the input current is and the output dc voltage vo.

S Components Capacitor voltages VC1 and VC2 must be higher than the peak value of the input voltage vs to ensure the control of the input current. For this case, the inductor voltage dynamic equation is In a similar way, in Fig. Other resonant topologies are described Equation Using a bipolar PWM switching strategy, this converter may have two conduction states: i Transistors On the other hand, the equivalent circuit of Fig.

In this topology, the output voltage vo must be higher than the peak value of the ac source voltage vs , to ensure a proper dis control of the input current. In this case, the inductor voltage is given by hence, for this condition, the input current is t increases.

This topology can T2 and T3 on. Here, the inductor voltage has the following present an unbalance in the capacitor voltages VC1 and VC2 , expression which will affect the quality of the control. The ripple amplitude of this current can be reduced by which means an increase in the instantaneous value of the decreasing the hysteresis width of the controller. Finally, Fig. To reduce the costs, the complete control sys- state of Fig. This can be done by replacing tem shown in Fig. Today there is increased interest in developing high-