DC Motor Drive Basics Part 4: Chopper-Fed DC Motor Drives
DC Motor Drive Basics - Part 4: Chopper-fed dc motor drives
Austin Hughes
11/11/2008 2:51 PM EST
[Part 1 begins with an overview of the operation of thyristor-fed DC motor drives. Part 2 continues with a look at converter output impedance, four-quadrant operation, single- and double-converter reversing drives and power factor and supply effects. Part 3 examines the operation of a standard dc drive system with speed and current control.]
CHOPPER-FED D.C. MOTOR DRIVES
If the source of supply is d.c. (for example in a battery vehicle or a rapid transit system) a chopper-type converter is usually employed. The basic operation of a single-switch chopper was discussed in Chapter 2, where it was shown that the average output voltage could be varied by periodically switching the battery voltage on and off for varying intervals. The principal difference between the thyristor-controlled rectifier and the chopper is that in the former the motor current always flows through the supply, whereas in the latter, the motor current only flows from the supply terminals for part of each cycle.
A single-switch chopper using a transistor, MOSFET or IGBT can only supply positive voltage and current to a d.c. motor, and is therefore restricted to quadrant 1 motoring operation. When regenerative and/or rapid speed reversal is called for, more complex circuitry is required, involving two or more power switches, and consequently leading to increased cost.
Many different circuits are used and it is not possible to go into detail here, though it should be mentioned that the chopper circuit discussed in Chapter 2 only provides an output voltage in the range 0 < E, where E is the battery voltage, so this type of chopper is only suitable if the motor voltage is less than the battery voltage. Where the motor voltage is greater than the battery voltage, a 'step-up' chopper using an additional inductance as an intermediate energy store is used.
Performance of chopper-fed d.c. motor
Austin Hughes
11/11/2008 2:51 PM EST
[Part 1 begins with an overview of the operation of thyristor-fed DC motor drives. Part 2 continues with a look at converter output impedance, four-quadrant operation, single- and double-converter reversing drives and power factor and supply effects. Part 3 examines the operation of a standard dc drive system with speed and current control.]
CHOPPER-FED D.C. MOTOR DRIVES
If the source of supply is d.c. (for example in a battery vehicle or a rapid transit system) a chopper-type converter is usually employed. The basic operation of a single-switch chopper was discussed in Chapter 2, where it was shown that the average output voltage could be varied by periodically switching the battery voltage on and off for varying intervals. The principal difference between the thyristor-controlled rectifier and the chopper is that in the former the motor current always flows through the supply, whereas in the latter, the motor current only flows from the supply terminals for part of each cycle.
A single-switch chopper using a transistor, MOSFET or IGBT can only supply positive voltage and current to a d.c. motor, and is therefore restricted to quadrant 1 motoring operation. When regenerative and/or rapid speed reversal is called for, more complex circuitry is required, involving two or more power switches, and consequently leading to increased cost.
Many different circuits are used and it is not possible to go into detail here, though it should be mentioned that the chopper circuit discussed in Chapter 2 only provides an output voltage in the range 0 < E, where E is the battery voltage, so this type of chopper is only suitable if the motor voltage is less than the battery voltage. Where the motor voltage is greater than the battery voltage, a 'step-up' chopper using an additional inductance as an intermediate energy store is used.
Performance of chopper-fed d.c. motor