Future Motion Applications requiringsmart and compact Motion Control

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Hardware-based motion control engine

Implementing motion control with inverters has been done for quite some time now. These systems usually deploy a DSP that provides the necessary computing "horsepower" to calculate the pulses required to accurately control the motors.

But there are many applications, like pumps, fans, slower-speed material transportation, motor-controlled solenoids, doors and windows, that do not require sophisticated functions at system level. In these applications, the motors are usually required to run at predefined, slow speeds, without much dynamic variation, and the power requirements will be relatively constant, requiring little dynamic regulation. But they will require small size, high efficiency and low system cost. Additional features that increase the value for the end customer can include some variation of the rotation speed, application fault recovery, displaying system status, and receiving some simple commands from the outside.

Now, using BLDC or PMSM motors is forcing engineers to use large DSPs, along with the programming and debugging tools required to develop software – usually a big step for companies that were not used to develop complex electronics and software at all. New products like Fairchild’s FCM8201, FCM8202 and FCM8531 close this gap. Here, the motion control algorithm is implemented with a dedicated hardware controller, called "Advanced Motion Controller", whereas the host control functions, like user interface, slow-speed protection functions, and communication, are implemented using a well-known microcontroller, based on the 8051 architecture. This division of tasks delivers the best of both worlds, while the high speed motion control engine will efficiently control the motor, the host is very easy to program.

The FCM8201 provides programmability at system level, to be able to not only debug systems efficiently but also monitor the system state during operation, and change the operation based on outside commands. The FCM8202 has the communication features removed, and is targeted towards systems that will not require any outside control, and it can be pre-programmed in the factory to deliver a drop-in solution. While these two controllers still require hall sensors or similar to detect the position of the rotor, the new FCM8531 is based on sensorless control. Instead, it evaluates the phase currents of the three inverter legs and uses the back-EMF of the motor to calculate the position and required pulses, further reducing system cost. The block diagram of the FCM8531 is shown in figure 3.

The advanced motion control engine is located on the right, consisting of a set of AD converters to take the sensor signals in, and a PWM engine that works with an angle detector to calculate the appropriate PWM pulses in hardware. Additional circuits are providing protection functions without relying on the processor to provide CPU time for these.

Performance advantages

While the move from AC to BLDC or PMSM motors alone will already improve system efficiency significantly, the algorithms used in these advanced hardware motion controllers will further increase efficiency, albeit not dramatically. But for the applications mentioned above, system size matters a lot, the ultimate goal being to integrate the electronic control circuits with the motor in a compact housing. A highly integrated controller obviously helps achieving this goal. And, time to market is significantly improved through completely documented reference designs and evaluation hardware that customers can use to shorten their design cycles, while time to implement the user interface and communication is vastly reduced due to the use of an industry-standard host controller. The picture below shows the compact implementation of a solution based on the FCM8201 and a SPM3 smart power module, recognizable by its copper-covered substrate.

Implementing new functionality

This host controller is also used to implement new functions, like changing speed (simply by issuing commands to the motion control engine), sense of rotation, user communication (both accepting user inputs as well as reporting the system state), accepting additional sensor inputs and controlling other functions in the system, like displays, relays, or solenoids. The implementation of these functions with previous motor types was very difficult and costly, and ruled out implementation for most applications where system cost is a driving factor.

Outlook: Using hardware-based motion controllers that enable compact system solutions with very fast time to market enable new levels of system performance. Further integration of the controller with the PFC stage, and eventually the system integration inside a smart power module will make these systems even more compact and their widespread adoption even easier.

* * Alfred Hesener... is Senior Director Marketing and Applications at Fairchild Semiconductor, Fürstenfeldbruck/Germany.

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