Are the gloves off for motor control?

During Embedded World, Toshiba Electronics Europe (TEE) introduced its first product offering to the European market, for vector control using a hardware based vector engine. Like ST's STM32, the TMPM370FY uses the ARM Cortex M3 core but instead of dedicating some of the core's power to performing the complex algorithms necessary for vector control, it employs a hardware-based vector engine, which the company believes offers significant advantages over a software-based implementation.

Frank Thimm is part of TEE's microcomputer, automotive and consumer IC marketing team for microcontroller and analog ICs. He believes the choice to implement vector control in hardware has attracted a lot of interest since the launch at Embedded World: "The main benefits of putting vector control in hardware are, from the software development point of view, it's much easier because the customer doesn't have to take care of the software. The system itself is more stable, with predictable functionality."

Although Toshiba has offered similar products to the Asian market for some time, this is the first product offering for the European market, and it includes the vector engine which offloads some of the computationally heavy lifting from the processor to the hardware. As such, the vector engine isn't a new development but it has been improved for use in the TMPM370FY. According to Toshiba, it made the decision to implement hardware acceleration at an early stage in the development of its motor control families, which complements the programmable motor driver circuit also present in the '370.

Thimm also claims the device can operate at a lower frequency, thanks to the vector engine: "The device can operate at 40MHz, a lower frequency than comparable general purpose microcontrollers providing vector control in software." It achieves this through the vector engine acting as a co-processor, to boost the performance of the cpu. In theory, the hardware resources of the vector engine are also available to accelerate other mathematical functionality " see figure 1.

Fig 1: Motor control " the software / hardware balance.

To see a bigger version of this graphic click here.

Early devices from Toshiba did actually implement vector control in software, but that was rapidly migrated to a hardware solution to work alongside the programmable motor driver circuit. It means that all calculations carried out for vector control are handled in the hardware based vector engine. "This is the next generation of vector control; the combination of the Cortex M3, vector engine and programmable motor driver results in a faster motor controller, able to control two motors in parallel."

It also performs the computations quicker, shortening the total control loop which creates more flexibility in how the motors are controlled.

With the latest device, Toshiba has also integrated more of the analog circuitry necessary for motor control applications, bringing it inside the device to create more of an 'application specific' solution " see figure 2.

Fig 2: The Toshiba TMPM370FY uses the ARM Cortex M3 core employs a hardware-based vector engine for preforming complex algorithms.

To see a bigger version of this graphic click here.

Like the STM32 from STMicroelectronics, TEE's TMPM370FY is also able to add sensorless feedback, which is necessary for vector control algorithms whether they be implemented in hardware or software.

Fig 3: Block diagram of the Toshiba TMPM370.

With the demand for more efficient, smaller and quieter motors set to continue or even increase over the next three to five years, it seems likely that both the solutions mentioned here will find application areas. Vector control as a technique is applicable to any form of three-phase motor but it would appear that the biggest benefits lie with coupling it with an advanced internal permanent magnet motor.

The fact that both the featured solutions have, at their heart, the ARM Cortex M3 should increase end-users' confidence in adopting vector control; as it affords them the flexibility to implement it using either a hardware or software based solution without compromising their application software.

This story appeared in the May 2009 print edition of Embedded Systems Europe

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