ARM Community: Optimized Motor Control with Toshiba's ARM Cortex-M3 Vector Engine MCUs - ARM Community

From refrigerator compressors to industrial pumps, micros that combine an ARM® Cortex™-M3 core with motor control firmware can help engineers rapidly create the optimum, low-energy motion control design.

In a world where we all want to cut costs and improve our green credentials variable speed BLDC motors play an increasingly important role. With suitable electronic control for adjusting their speed, power and torque according to demand and operating conditions, they not only cut energy costs and reduce carbon emissions but also help minimise acoustic and electrical noise. Can’t hear your washing machine or dishwasher? Then thank a variable speed motor (and some very clever drive electronics).

Designers are looking to capitalise on these benefits at the same time as building differentiating features into their products. But resources aren’t getting any more plentiful, time-to-market isn’t getting any shorter and end users don’t expect to pay more. A key issue for designers, therefore, is the software development/re-use trade-off to create the optimum system. Which is why ARM processor-based platforms with the flexibility to choose complete software control, majority hardware control and everything in between make things significantly simpler.

Toshiba ARM Cortex-M3 processor-based MCUs with Vector Engine

As the first intelligent motor controls evolved, signal processing using a DSP was seen as the highest performing technique for computing motor-control waveforms based on parameters such as rotor speed, position and user demand. An alternative has been to choose a microcontroller (MCU) with dedicated motor-control IP integrated in hardware. More recently, the advent of the ARM Cortex-M3 32-bit embedded core enables MCUs to host fully software-based motor control.

At Toshiba we have developed a new type of Cortex-M processor series-based micro that can be connected to almost any preferred power section and that has motor-control IP implemented as firmware. The TMP37x series promises the best of all worlds: a cost-effective, customisable solution capable of high performance that also has sufficient processing capacity to support value-added features and functions such as motor emergency stop or HMI management. As firmware, the motor-control IP allows developers the flexibility to use only the functions they need, without having to accept high silicon overheads.



This picture illustrates how the MCU integrates Vector Engine (VE) and Programmable Motor Drive (PMD) blocks. Together, these functions execute a Field Oriented Control (FOC), also called Vector Control (VC), algorithm, which provides the basis for smooth and responsive control without the high demand on processing power imposed by traditional sinusoidal control techniques at high rotor speeds.

On-board motor control with Toshiba MCU

FOC manipulates the motor currents and voltages with reference to the rotor axes by ensuring the stator field remains constant and in quadrature with the rotor field. The sensed stator currents are transformed into two vectors acting in line with the rotor (D) and in quadrature (Q). For maximum torque, the D vector is compared with zero and the Q vector is compared with the torque requested by the application. The resulting error signals drive a Proportional-Integral (PI) function that calculates signals referenced to the rotor axes. These are then transformed into the stator domain to generate the corresponding PWM signal for each phase. In this way, FOC is independent of any bandwidth limitations of the PI controllers. The result allows the motor to deliver its maximum torque accurately, even at high rotor speeds.

The PMD block implements a 3-phase PWM generator, dead-time controller, protection circuit and ADC timing network. Working in combination with these functions, the VE enhances efficient motor control by offloading resource-hungry computations from the main CPU. Within the VE block, a scheduler for event and priority control, a calculation core and decoder, an operation unit, a multiply-accumulate unit and vector control modules handle processing of the 3-phase current input from the MCU’s ADC and perform the FOC algorithm.

With only a few simple register settings required, the PMD and VE firmware work together to manage all of the functions needed to control a motor, including three-phase PWM waveform generation at 16-bit resolution, speed control and position estimation. The MCU integrates a 12-bit ADC, providing high-speed PWM-synchronised analogue-to-digital conversion. The on-board programmable amplifiers allow flexible gain setting for the phase currents.

By implementing these functions in firmware, the MCU gives developers the freedom to combine functions from the PMD block with any proprietary motor control IP if required. Unlike a rigid, hardware-based approach, the PMD firmware imposes no penalty in terms of unused silicon if the developer chooses to implement certain parts of the algorithm using proprietary functions.

Guest Partner Blogger:
Roland Gehrmann is the manager for Consumer and Industrial IC marketing at Toshiba Electronics Europe (TEE). Based at TEE’s headquarters in Düsseldorf, Roland is responsible for the company’s European microcontroller marketing with a specific focus on ARM9 and Cortex M3 for industrial and home appliance applications. He has held several senior marketing and engineering management positions within Toshiba and, prior to his latest role, was responsible for MCU business development at Toshiba America Electronic Components, Inc. Roland has an electrical engineering degree from the University of Muenster, Germany.

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