POWER ELECTRONICS Instructor: Eng.Moayed N. EL Mobaied The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department بسم الله الرحمن الرحيم EELE 5450 — Fall Lecture 11

Chapter Four The Single-Phase Full-Wave Phase-Controlled Converter Using the Bridge Principle Center-tap transformer (essential)

Chapter Four The Single-Phase Full-Wave Phase-Controlled Converter Using the Bridge Principle When the input transformer is not essential, a bridge system is often more economical. There are several variations of the bridge circuit using one thyristor, two thyristors, or four thyristors. There are five different circuits of single-phase controlled bridge. All the circuits are shown with inductive load.

Chapter Four 1-Circuit with two thyristors and two diodes This circuit is not acceptable with inductive load. The inductive load energy would free-wheel through : With high L/R ratio (time constant),the thyristors will forces to conducts with out trigger pulses. This circuit is not acceptable with inductive load. The inductive load energy would free-wheel through D1 and Th1 or D2 and Th2.

Chapter Four 2-Bridge with two thyristors and two diodes,plus a free- wheeling diode. In this case, the free-wheeling diode (being of lower impedance than a thyristor and diode in series),D3, allows the circulation of the stored energy of the load. Also in the transient (during off state) D3 clamps the transient voltage, so the thyristors do not see any high voltage spikes.

Chapter Four 3-Bridge with two thyristors and two diodes. In this case, the energy in the load inductance circulates through diodes D1 and D2 when the thyristors are not conducting. Hence the two diodes of the bridge act as free-wheeling rectifires. Current duty in the diodes is large.

Chapter Four 4- One thyristor and five diodes in abridge connection. In many phase-rectifier dc motor drives this configuration of the bridge. The rectified full-wave voltage is then controlled by thyristor Th1. Used in Dc motors control.

Chapter Four 5- Bridge circuit with four thyristors. Only, between the above circuit, this circuit can contains negative voltage.For α 90 as inverter. (if L is large)( ch7) End of Lecture **** Eng.moayed