Electric Drives
Introduction
Electrical drives
Motion control is required in large number of industrial and domestic applications like transportation systems, rolling mills, paper machines, textile mills, machine tools , fans pumps , robots, washing machine etc.. system employed for motion control are called drives and employ any of the prime movers such as diesel or petrol engines gas or steam engines hydraulic motors and electric motors for supplying mechanical energy for motion control. Drives employing electric motors are known as Electrical drives.
Fig 1.1 Block diagram of an Electrical Drive
The advancement in electric drive system is very much related to the development in the power semiconductor devices technology. The introduction of the Silicon Controlled Rectifier (SCR) in 1957 has initiated the application of solid state devices in power converters. The development of the electrical drives systems can be divided into three stages Before power semiconductor devices were introduced: AC drives were used for fixed speed operation. Generating an AC voltage with variable frequency was only possible by using rotary converters, which are bulky and inflexible. Although it is possible to use variable voltage with fixed frequency sources (for example using transformers) to control the speed of AC motors, the efficiency of the drive system will be very poor especially at low speeds. On the other hand, variable DC supply can be produced using multi-machine configuration and hence could be used to control the armature voltage of the DC motors. Consequently, DC drives are widely used for variable speed operation, whereas AC machines were used mainly for fixed speed applications. After power semiconductor devices were introduced in 1950s
Although self turnoff devices (Bipolar Junction Transistor – BJT) were available in the 1950s their voltage ratings were too low which make them inappropriate to be used in power circuit. Silicon-Controlled Rectifier (SCR) was introduced
Electrical drives
Motion control is required in large number of industrial and domestic applications like transportation systems, rolling mills, paper machines, textile mills, machine tools , fans pumps , robots, washing machine etc.. system employed for motion control are called drives and employ any of the prime movers such as diesel or petrol engines gas or steam engines hydraulic motors and electric motors for supplying mechanical energy for motion control. Drives employing electric motors are known as Electrical drives.
Fig 1.1 Block diagram of an Electrical Drive
The advancement in electric drive system is very much related to the development in the power semiconductor devices technology. The introduction of the Silicon Controlled Rectifier (SCR) in 1957 has initiated the application of solid state devices in power converters. The development of the electrical drives systems can be divided into three stages Before power semiconductor devices were introduced: AC drives were used for fixed speed operation. Generating an AC voltage with variable frequency was only possible by using rotary converters, which are bulky and inflexible. Although it is possible to use variable voltage with fixed frequency sources (for example using transformers) to control the speed of AC motors, the efficiency of the drive system will be very poor especially at low speeds. On the other hand, variable DC supply can be produced using multi-machine configuration and hence could be used to control the armature voltage of the DC motors. Consequently, DC drives are widely used for variable speed operation, whereas AC machines were used mainly for fixed speed applications. After power semiconductor devices were introduced in 1950s
Although self turnoff devices (Bipolar Junction Transistor – BJT) were available in the 1950s their voltage ratings were too low which make them inappropriate to be used in power circuit. Silicon-Controlled Rectifier (SCR) was introduced