Digital Motor Control:
C2000 32-bit Real-time Controllers

Digital Motor Control Library

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DMC Systems: Piccolo & Delfino

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DMC Systems: Legacy Fixed-Point Series

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IQMath: Virtual Floating Point

IQMath is a library and compiler intrinsic for the C28x generation that allows you to select your range (and hence your resolution) by choosing which bits of your binary represented number are integer (I) and which are the quotient (Q). It also allows you to write C functions in floating point format instead of dealing with fixed point scaling, and the compiler takes care of the rest.

• Start-up, tuning, and debug effort are reduced
• Change numerical range on the fly, global or local
• Tune for best resolution and dynamic range
• Remove quantization effects
• Reduce scaling and saturation burden
• Better integration with simulation and code gen tools
• Single source set to move between fixed and floating point processors
• Easy re-use and re-tuning for new systems

Real-Time Debug

• Implemented in silicon, not by a software debug monitor
• No CPU cycles required
• RTDX always available, real-time debug on customer returns
• Halt in non-critical code for debug while time-critical interrupts continue to be serviced
• Access memory and registers without stopping the processor

System Considerations

The latest Piccolo family of devices includes the latest advances with the following goal in mind:

To Lower System Cost and Increase System Reliability:

• On-chip voltage supervisor with POR/BOR eliminates external supervisor and has in built-in features to eliminate start-up glitches on all PWM pins
• Three Tier Clock Protection for IEC-60730
• Two internal and optional external oscillators
• Two watchdogs and clock fail detection circuitry automatically switches to back-up OSC
• If both internal fail device automatically goes into limp mode with graceful shutdown
• GPIOs include internal digital filter which reduce noise and saves external system cost

In most countries outside of the United States we also see regulatory bodies mandating inclusion of Power Factor Correction (PFC) into most new white goods, and we expect this to spread to other industries.

• Problem
• A 3-phase inverter and motor act as a non-linear load and draw harmonic currents from the provider's line. These harmonics result in losses and distortions.
• Solution
• PFC guarantees the current waveform drawn follows the voltage waveform of the line and also regulates the output DC voltage to a constant value regardless of any changes in the load or the input conditions.
• Analog vs. Digital PFC:
• Analog or passive implementations of PFC are locked into a single mode and have a limited ability to react to changes in operating conditions.
• Active or digitally controlled PFC, in contrast, can act on and adapt to changes in operating conditions and it can be more precise and eliminate any phase shift between voltage and current, increasing efficiency.
• The flexibility of digital PFC also enables developers to employ more complex PFC topologies than is possible with passive implementations.
• C2000 devices have the processing headroom and high resolution ADCs and PWMs to implement PFC with sensorless FOC control (and dual axis FOC) even with our lowest cost Piccolo MCUs
• Example hardware and software are included in all Piccolo and Delfino solutions.

Graphical Simulation and Code Development

Both the Mathworks Embedded Target and Visual Solutions VisSim support graphical motor control development tools that target C2000 MCUs (and interface seamlessly to existing DMC hardware). These tools offer:

• Block support for the TI DMC Library and other TI device, math, and peripheral libraries
• Simulation, modeling, and validation of complete DMC systems
• Auto-tuning and Co-efficient finders
• Code generation and target deployment
• Direct interface to TI's Integrated Development Environment and hardware development tools

C2000 Device Features

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Key Features for Motor Control

C28x CPU

The C28x 32-bit DSP is the premier computational engine for Digital Motor Control.

• Offers the highest precision and fastest throughput for computationally intensive algorithms.
• DMC Library based sensorless FOC takes ˜12 MIPS
• Extended performance
• Delfino family offers single precision floating point unit
• FPU is an extension of the fixed point core and provides about a 50% cycle improvement in the core DMC algorithms
• In the Piccolo family we are offering an optional Control Law Accelerator (CLA)
• CLA is a floating point parallel processing unit that has independent control of the ADCs and PWMs
• Was designed for very high speed, low latency control loops in digital power applications
• In process of releasing a CLA DMC Library and System Examples that will allow the core DMC functions to be "black boxed and off-loaded" into the CLA, allowing the C28x CPU extra bandwidth for other system functions

A/D Converter

The ADC on every F28x device has a common ancestry, but has been improved upon in each successive series with more accurate references, better auto-calibration, and DMA support.

• 12-bit ADC converter with up to 12.5 MSPS throughput
• Two sample and hold circuits for simultaneous sampling
• Single or dual bank sequencer with flexible start of conversion and 16 result registers
• The latest Piccolo family supports ratiometric operation, a more flexible sequencer, adjustable acquisition window, and a just-in-time feature which allows the ADC to pre-call the CPU interrupt to synchronize availability of the converted sample with the CPU

PWM Generation

The ePWM modules provide the industry's most feature-rich and flexible PWM pattern generation.

• Each ePWM module has an independent shadowed 16-bit time base (count up, down, or up-down) that can produce two duty cycle independent outputs
• There is an optional rising and falling edge dead-band generator, high frequency chopper, and programmable trip zone
• The trip zone operates even if the MCU clocks go missing, and allows you to map an external pin to any combination of PWM output states, interrupts, ADC start of conversion, or PWM synchronization signals. The trip can be synchronous or asynchronous, has an off-set window, and can be run in cycle by cycle or one-shot modes
• Independent ePWM blocks can be synchronized to a common time base or automatically phase delayed
• Standard PWM resolution is tied to the system clock, but there are also High Resolution PWMs with as accurate as 55ps resolution, and the Piccolo family offers High Resolution precision on both the duty cycle and the period.