ELECTRICAL MACHINES

Digital Recording Definition

Digital Recording Definition: Digital Recording Definition- Digital magnetic tapes are often used as storage devices in digital data processing applications. Digital tape units are of two types, incremental and synchronous. Incremental digital recorders are commanded to step ahead (increment) for each digital character to be recorded. Input data may be at a relatively slow, or […]

Vector Control of an Induction motor

Vector Control of an Induction motor: Vector Control of an Induction motor – The sole idea behind the vector control of induction motor is to have an electrical drive which must offer superior performance than widely used separately excited dc motor in industry. Further such a drive should also emerge as a robust, reliable, maintenance […]

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 […]

Single Phase Bridge Inverter

Single Phase Bridge Inverter: A serious disadvantage of the Single Phase Bridge Inverter of Fig. 11.46 is that it requires a 3-wire dc supply. This is overcome by the commonly employed full-bridge inverter circuit of Fig. 11.48(a) which needs four thyristors and four free-wheeling diodes. The sequence of thyristor gating and the output waveforms are […]

Single Phase Half Bridge Inverter

Single Phase Half Bridge Inverter: Figure 11.46(a) gives the circuit configuration of a Single Phase Half Bridge Inverter. It has two thyristors and two free-wheeling diodes. Each thyristor is gated at frequency f= 1 /T of the ac supply desired. The gating signals of the two thyristors have a phase angle of 180°. From Fig. […]

Phase Control of Induction Motor

Phase Control of Induction Motor: Figure 11.44 shows the schematic representation of  3 Phase Control of Induction Motor. Two thyristors are connected in antiparallel in each line. The firing sequence of the thyristors for all modes of operation is 1, 3′, 2, 1′, 3 and 2′ as shown in Fig. 11.45. The interval between successive […]

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