Forced Commutation

Forced Commutation: It was observed from the discussion on choppers and inverters that in thyristor systems fed from dc supply, the forward current does not pass through zero naturally and must therefore be forced to become zero at appropriate instants by means of auxiliary circuitry, called the commutation circuit. Apart from forcing the forward current […]

Sinusoidal Pulse Modulation

Sinusoidal Pulse Modulation: In Sinusoidal Pulse Modulation the pulse-width instead of being uniform as in the waveform of Fig. 11.55 is a sinusoidal function of its angular position with respect to a reference sine wave resulting in a reduction in the harmonic content. The control function consists of a sinusoidal wave obtained from an oscillator […]

Voltage and Harmonic Control of Inverters

Voltage and Harmonic Control of Inverters: In applying Voltage and Harmonic Control of Inverters for motor control both V andf(keeping V/fconstant) need to be varied. Further, the inverters apply essentially nonsinusoidal ac voltage to the motor. External filter circuits cannot be employed due to the difficulty in operating inverters over a wide range of frequencies. […]

Three Phase Bridge Inverter

Three Phase Bridge Inverter: Three Phase Bridge Inverter – The basic 3-phase inverter is a six-step inverter. A step is defined as a change in the firing sequence. A 3-phase thyristor bridge-inverter is shown in Fig. 11.49. Th1 to Th6 are the six load-carrying thyristors while D1 to D6 are the free-wheeling diodes. Each pair […]