TAILIEUCHUNG - Electric Machinery Fundamentals Power & Energy_5

Tham khảo tài liệu 'electric machinery fundamentals power & energy_5', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Figure b 3 If S CR1 and SCR4 are now triggered again the voltages across capacitors C1 and C2 will force SCR2 and SCR3 to turn OFF. The cycle continues in this fashion. Capacitors C1 and C2 are called commutating capacitors. Their purpose is to force one set of SCRs to turn OFF when the other set turns ON. The output frequency of this rectifier-inverter circuit is controlled by the rates at which the SCRs are triggered. The resulting voltage and current waveforms assuming a resistive load are shown below. SCRỆ AN SC4U N AM search 3-13. A simple full-wave ac phase angle voltage controller is shown in Figure P3-8. The component values in this circuit are R 20 to 300 kQ currently set to 80 kQ C AF 83 VBO 40 V for PNPN Diode D1 VBO 250 V for SCR1 vs t VM sin cot volts where VM V and o 377 rad s a At what phase angle do the PNPN diode and the SCR turn on b What is the rms voltage supplied to the load under these circumstances Note Problem 3-13 is significantly harder for many students since it involves solving a differential equation with a forcing function. This problem should __only be assigned if the class has the mathematical sophistication to handle it. Solution At the beginning of each half cycle the voltages across the PNPN diode and the SCR will both be smaller then their respective breakover voltages so no current will flow to the load except for the very tiny current charging capacitor C and vload t will be 0 volts. However capacitor C charges up through resistor R and when the voltage vC t builds up to the breakover voltage of D1 the PNPN diode will start to conduct. This current flows through the gate of SCR1 turning the SCR ON. When it turns ON the voltage across the SCR will drop to 0 and the full source voltage vS t will be applied to the load producing a current flow through the load. The SCR continues to conduct until the current through it falls below IH which happens at the very end of the half cycle. Note that after D1 turns on .

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