Workings of Motor Drives

BRUSHLESS DC & BRUSH DC MOTOR DRIVES

Drives are selected according to the movement needed. The first question to answer before selecting the drive is to define if the movement is a spindle application (constant speed) or an incremental motion. Then it's important to define movement made by the motor.

• Point-to-point
• Point-to-point following a trajectory
• Point-to-point following a velocity profile

To make the motion, we need to define the torque and speed the motor will have to deliver, and thereby the current and voltage needed by the driver. The motor can be driven with simple voltage applied to the coil – voltage drive – or the current can be controlled in the coil – current drive. Usually voltage drive is used for simple applications, mainly one working point. Current source allows control of the torque delivered by the motor. The current can be controlled either by a linear amplifier or, as with most drivers today, PWM to regulate the current.

Drives for DC and Brushless DC motors
A simple way to drive a DC motor at constant speed is to use RI compensation. (The Portescap Team can help you to design such drives.) For more complex applications, Portescap has developed a drive for DC and brushless DC that can deliver up to 12A peak and work up to 48V. Such drives can receive consign through RS232 or CANopen. Feedback needed are encoder signal and hall sensors for the brushless DC commutation. This driver can be operated in current, velocity or position mode.

Drivers for Steppers
There are many ways to drive steppers. A drive for a stepper usually requires input direction and pulses. For each pulse the drive will generate current in each motor phase to move the rotor of one step or microstep. According to the drive, the motor can be driven in full step, half step or microstepping (according the current applied in each phase). Simple drives do not use current regulation in the coil – they are equivalent to voltage drive; we call them L/R type. For such drive it can be an advantage to add a resistance to decrease the electrical time constant. More complex drive use current regulated in each coil through a PWM. With current adjusted in each coil, the motor can be driven in micro steps. Today another way to drive a stepper is a servo motor; this give all the advantages of a stepper and of the servo. (The Portescap Team will be pleased to assist you if you are interested to trying this option.)