MOTOR CONTROL

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 […]

Pulse Width Modulation Inverter

Pulse Width Modulation Inverter: In presenting the arguments here attention will be focussed on a single-phase inverter. Instead of the single rectangular pulse output of Figs 11.46 and 11.48 during each half-cycle, a commutation circuitry can be devised to produce a series of short duration pulses as output in each half-cycle as shown in Fig. […]

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 […]

Static Kramer Drive

Static Kramer Drive: The Static Kramer Drive variable-speed drive system shown in Fig. 11.43 consists of a slipring induction motor and a rectifier-fed dc motor. The machines are connected electrically in cascade. The slip power recovery takes place through the rectifier and the auxiliary dc motor. Torque supplied to the load is sum of torque […]

Static Scherbius Scheme

Static Scherbius Scheme: Static Scherbius Scheme – A basic scheme of a Scherbius static-converter cascade, that is employed for recovery of slip power in electrical form itself, is given in Fig. 11.42. For achieving both subsynchronous and supersynchronous speed control, converters C1 and C2 must be fully-controlled thyristor bridges, one functioning at slip frequency as […]

AC Motor Control

AC Motor Control: AC Motor Control – The only way to control the speed of a synchronous motor is to control the input frequency and voltage such as to keep V/f constant. The induction motor, on the other hand, can be controlled by the following means: 1. Stator Voltage Control This is applicable for small […]

DC Motor Control through Choppers

DC Motor Control through Choppers: DC Motor Control through Choppers – For controlling a dc motor operated from dc supply, the dc voltage level must be controlled. Examples can be cited of subway drives, trolley buses or battery-operated vehicles. Conventional methods of converting a fixed-voltage dc source to a variable-voltage dc source are: Resistance Control […]

Three Phase Converters

Three Phase Converters: Large-kW motors are fed from 3-phase supply through three Phase Converters. In a Three Phase Converters, the ripple frequency of the motor terminal voltage is higher than that in the single-phase converter, as a result the filtering requirements for smoothing out the motor current are less and the current is mostly continuous. […]

DC Motor Control through Converters

DC Motor Control through Converters: DC motor control is conveniently and efficiently achieved by phase-controlled converters wherein the ac input voltage is converted to a controlled dc output. The commutation process, the transfer of current from one thyristor to the other, in these converters is the inexpensive natural or line commutation. As, an incoming thyristor is […]

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