DSP Motor Control Boosts Efficiency In Home Appliances

The control software for the washing machine application was developed for an ADMC331 motor control IC. The challenge for this controller was to run four simultaneous control loops where the variables have a very wide dynamic range. A solution, which very much improved performance, was to use floating point variables for all the PI control loops. This extended the processing time somewhat but was not found to be a significant burden when using a 25 MIPS DSP core.

The processor must handle multiple interrupt sources from the ADC, the digital I/O block, the communication ports, and the timer. A number of useful device features such as an autobuffered serial port and a single context switch made the task possible without significant overhead in pushing or popping a stack. Finally, the code development was somewhat simplified by the availability of library functions on the ADMC331 ROM for mathematical functions and the Park and Clark transformations.

The availability of DSP microcontrollers presents a new set of challenges for motor-control design engineers. The vast increase in processing power over standard microcontrollers offers an opportunity to increase drive performance or reduce cost. The two examples given here show that to fully employ this power requires new control approaches and philosophy. The challenge will be to fully exploit the opportunities possible with this new technology. The world of domestic appliances is changing in a similar fashion as the automotive industry changed a few years ago. The future is a world of "intelligent" home appliances.

The control software for the washing machine application was developed for an ADMC331 motor control IC. The challenge for this controller was to run four simultaneous control loops where the variables have a very wide dynamic range. A solution, which very much improved performance, was to use floating point variables for all the PI control loops. This extended the processing time somewhat but was not found to be a significant burden when using a 25 MIPS DSP core.

The processor must handle multiple interrupt sources from the ADC, the digital I/O block, the communication ports, and the timer. A number of useful device features such as an autobuffered serial port and a single context switch made the task possible without significant overhead in pushing or popping a stack. Finally, the code development was somewhat simplified by the availability of library functions on the ADMC331 ROM for mathematical functions and the Park and Clark transformations.

The availability of DSP microcontrollers presents a new set of challenges for motor-control design engineers. The vast increase in processing power over standard microcontrollers offers an opportunity to increase drive performance or reduce cost. The two examples given here show that to fully employ this power requires new control approaches and philosophy. The challenge will be to fully exploit the opportunities possible with this new technology. The world of domestic appliances is changing in a similar fashion as the automotive industry changed a few years ago. The future is a world of "intelligent" home appliances.