Appliance Design - October 2007 - (Page 25)

MOTORS This allows the developer to modify the control algorithm directly making use of a library of optimized control blocks such as PI compensators and vector rotations. One example of an optimized control block is the vector rotator shown in Fig. 4. The CORDIC vector rotation has been developed specifically for ASIC implementation that relies on a series of add, subtract, and shift functions that yield 12-bit accuracy in only 13 cycles [citation 1]. This calculation is 10 times faster than the calculation using Taylor expansion on a 32bit RISC processor. The optimized control blocks enable a significant reduction in execution time relative to software implementations. This allows the MCE to execute the sensorless field-oriented control algorithm twice in a PWM cycle and simultaneously control two permanentmagnet synchronous motors. This Analog Signal Engine includes a fast A/D converter, multiple sample and hold circuits and buffer amplifiers for signal conditioning that allow it to measure the winding currents in two motors. There is additional signal conditioning and MCE processing capacity to support the execution of a power factor control (PFC) algorithm. As a result, the air-conditioning control IC can control the input power factor, the fan motor, and compressor motor while traditional RISC-processor-based systems require separate fan and PFC control ICs. < For more information, enter number 304 Or email: amurray1@irf.com Fig. 4. Vector rotation hardware. derivatives of cosine and sine flux functions, and so they can be determined through integration. The detailed control schematic for angle and speed estimator shown in Fig. 3 has two major subsystems. During the first stage, the flux estimator derives the rotor cosine and sine flux functions. The flux integrators include low-frequency gain compensation to avoid DC saturation. At the second stage, the rotor-angle, phase-locked-loop (PLL) forces the error between the rotor angle and the estimated angle to zero. The error is calculated using a vector-rotation function whose quadrature output will be zero when the rotation angle input matches the angle of the cosine and sine flux functions. The second-order feedback loop in the PLL generates both angle and velocity signals. A further feature of the PLL is the start-up sequencer that is required at low speeds when the winding back-EMF signal is swamped by circuit noise. The first part of the start-up sequence is a parking function that drives www.applianceDESIGN.com DC current into the stator windings to align the rotor at a known angle. Then the motor is driven with a constant current to generate a constant torque. The PLL speed integrator is fed by a motor mechanical model that estimates the motor speed from the accelerating torque and system inertia. Once the motor reaches a certain minimum speed, the PLL switches to a closed-loop mode and tracks the rotor flux angle. [Citation 1]. Ray Andraka, “A survey of CORDIC algorithms for FPGA based computers”, Proc. of ACM/SIGDA Sixth International Symposium on FPGAs, 1998, Monterrey, CA, pp. 191-200. The motion control engine When using a traditional DSP or RISC processor, the motorcontrol schematic is first translated into state equations that are written in C code before software development tools can generate machine code for the processor. The Motion Control Engine supports a unique approach to motor-control algorithm development. The MCE graphical compiler is an algorithm development tool that transforms the control schematic directly to MCE sequencer code avoiding all intermediary steps. For more Information Enter 111 applianceDESIGN AD07064Favi.indd 1 October 2007 25 6/6/06 4:05:13 PM http://www.favi.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - October 2007

Contents Editorial Shipments/Forecasts News Watch Applying Powder Coatings to Plastic Parts is No Longer a Pipe Dream New Technology Platform Provides the Ability for a single IC to Control Two- Motors in a Single Appliance, Simplifying Motor Control Design Advanced Motor-Control Techniques have Become More Accessible to a Wider Array of Appliances, Helping to Improve Efficiency and Reduce Noise Adding USB Host Capability to Appliances Permits In-Field Programming and Acquisition of Test Data ZigBee Modules Make it Easier to Design Wireless Connectivity into Applications New Concepts such as Rapid Tooling and Rapid Injection Molding Provide Stepping Stones Between Prototyping and Full Scale Production A Number of Factors and New Developments Affect the Decision on Whether to Build Prototypes In-House or Outsource to a Service Bureau DesignMart Advertiser’s Index Association Report: CEA

Appliance Design - October 2007

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