2009

Intelligent Motor Control ICs Simplify System Design

A new category of IC called an intelligent motor controller (IMC) is evolving that simplifies the task of designing high performance motor control drives. IMCs are dedicated, highspeed ICs that control multi-phase motors such as brushless DC and AC induction motors, and provide sophisticated control features required by today’s energy-efficient applications such as variable speed, flux vector control, and even sensorless control.

altThanks to new developments in MOSFETs, IGBTs, and DSP-based control, motor amplifiers have never been more compact and efficient. But even with these innovations, cost-conscious engineers must choose between purchasing an off-the-shelf amplifier, and designing a low-cost amplifier from scratch.

Now, an important third option has emerged with the development of a new type of IC known as an intelligent motor controller (IMC). IMCs are programmable single-IC controllers that provide high-level functions such as digital torque control, sinusoidal commutation, field oriented control, Hall sensor input, and overtemperature management. At the same time, it directly inputs torque and velocity commands, and outputs six high side/low side signals with shootthrough protection for use with an external MOSFET or IGBT switcher.

Figure 1 shows the internal block diagram of a typical intelligent motor controller IC. It provides microprocessorstyle command input, and can accept torque or velocity commands through a direct analog voltage, or SPI (Serial Peripheral Interface). While it has a DSP-like engine at its core, it is not a general purpose microprocessor. IMCs provides ready-to-go high level instructions appropriate for setting up the motor drive parameters such as “set current gain”, or “set output value”.

What types of motors can IMCs control? The short answer is multiphase motors, particularly brushless DC motors and multi-phase AC induction motors. IMCs primarily serve higher power, larger motor markets with drives of 1KW all the way up to 500KW. Step motor drive ICs, while multi-phase, are not generally included in the category of intelligent motor controller IC because they do not drive high power motors.

As it turns out, dedicated motor controller ICs have been around for a long time. In particular, low-cost ICs that control specific applications such as step motors, or brushless motors for disk drives, have been available for years. What is different about IMCs is that they serve general motor control markets where the motor size or load characteristics are not known in advance.

Another factor is that older dedicated motor controllers cannot said to be ‘intelligent’ because they lacked microprocessor command interfaces such as SPI (Serial Peripheral Interface), serial RS232, or CANBus. This is particularly important as more industries look to control motors at very high efficiency. IMCs can control a wide variety of motor sizes, drive voltages, and output currents.

altWhile intelligent motor controller ICs are available from several different vendors, one example of such a product is the MC73110 from Performance Motion Devices (see Fig. 2.). This compact 64-pin IC provided in a high density surface mount package, provides commutation, field oriented control, and MOSFET or IGBT excitation for a 3-phase brushless DC motor. It can be purchased with a developer’s kit and reference schematic that makes it easy to build a custom high performance motor drive.