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How to improve motor control and efficiency using FOC

How to improve motor control and efficiency using FOC

Electric motors are one of the largest consumers of power electronic designs. International environmental directives, commercial considerations and customer expectations mean that driving motors in a way that is as energy efficient as possible is a major consideration for engineers.

Among the most commonplace methodologies for driving electric motors are:

  1. Trapezoidal control, which is simple to implement, has low related component costs and is highly suited to space-constrained environments. However, accuracy of control can be a concern, especially when running at low speeds. As well as impacting smooth operation, this can lead to unwanted noise and impact overall system efficiency.
  2. Sinusoidal control, which uses phase-shifted sinusoidal current waveforms to produce a smoother torque response than the trapezoidal methodology. This requires more accurate rotor position information and requires that current values are calculated rapidly. At higher speeds, any lag in this calculation will lead to inefficiency
  3. Field oriented control (FOC), which has seen widespread uptake over the last few years and is fundamentally more efficient than either traditional trapezoidal or sinusoidal motor driving techniques.

In principle, FOC can offer efficient operation that spans all motor speeds. It addresses the inferior low-speed accuracy of trapezoidal control and does not suffer the lag issues that impacts sinusoidal control efficiency when the motor is running at high speed. FOC does, however, demand the rapid translation of sensed stator current signals into voltage control signals. When this is done in software this can put a heavy burden on a system’s processing resource. If not addressed properly, this potentially limits the motor speeds that can be achieved.

TCM0129_BlockDiagram

Instead of trying to tackle the problem purely in software, a better solution can be to make use of dedicated FOC hardware. However, hardware-based solutions can be inflexible and give engineers little scope to optimise the system to suit specific application criteria. The Vector Engine (VE) incorporated into a growing number of Toshiba’s ICs, however, provides the best of both worlds.

The VE is an adaptable FOC motor driving platform that embeds complex vector control equations alongside customisable firmware. This significantly diminishes the software overhead, reducing the associated processing workload while supporting increased motor speeds and curbing energy consumption. Engineers are given the ability to develop their own proprietary IP or make use of the existing IP that is provided with the platform.

To learn more about the latest innovations in motor driving technology and associated microcontrollers, please click here.

Click here to download the whitepaper

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·Before creating and producing designs and using, customers must also refer to and comply with the latest versions of all relevant TOSHIBA information and the instructions for the application that Product will be used with or for.