Helpful Information on How to Electronically Drive a DC Motor
It is important that any project that has to do with the control of speed, such as general movement, robotics traction, or even wheelchairs for that matter, has some or other way to control this speed in an efficient way. Any project requires a simple starting point, which is why the implementation of a driver that will perform this function became very necessary. Only after this part of a project is complete, should it be fine-tuned by adding indicators and special safety devices that will prolong the life of the whole.
Controlling the speed of a DC motor implies that you need to control the current through its armature. In industrial application, this is performed extremely effectively with the help of SCRs or controlled rectifiers. Devices like these quite simply control the current going to the armature by means of firing the SCR at different times on the cycle. However, you should understand that when the source of your power is already DC, the efficient way to do it is through PWM (pulse with modulation).
Note that other methods are mostly inefficient. One such an example is variable voltage power supply, simply because lots of energy is dissipated on internal circuitry resistors, and if you are operating your project from batteries they will be weak fairly quickly.
Thus, as can be derived from above, efficiency is of a very high importance indeed. With “Pulse With Modulation” (PWM), the DC voltage is chopped, subsequently producing a square wave where the on time can be controlled from. Even though the pick voltage of the wave will remain the same, the effective current will average if you can control the on to off ratio. This will control the energy to the armature, even though what you really get is a pulsating DC. There is no need to filter this because the armature inductance will handle that.
Separating the armature from the field circuitry is necessary in order to control the direction of the rotation of the motor. This means that serial DC motors cannot be used at all. Important to remember here is that the chopper needs to have the ability to reverse polarity only to the armature without changing polarity on the field. This is usually accomplished by four switching transistors in “H” configuration. Only two will be active at any time, providing negative and positive to the armature. When the other two are active, the polarity will reverse, thus reversing the rotation of the motor.
Types of DC Drives offered by EP Normand
The following types of DC Drives are offered by EP Normand:
