International Appliance Manufacturing 2007

PMSM control will yield considerable energy and cost savings. Toward this end, efficient motor control is the key to a better appliance. Latest Signal Controllers Benefit Appliance Design Advances in semiconductor technologies have resulted in Digital Signal Controllers (DSCs) and power electronic switches that can be used to build motor drives with variable speed. In fact, thanks to DSCs efficient and cost-effective motor power management, appliances need not be held hostage to a few custom hardware and control techniques. In particular, with the latest generation of Microchip’s dsPIC™ DSC family, it is now possible for appliance makers to design motor systems that could result in a significant energy and cost savings. This is because the specialized peripherals on the Microchip dsPIC DSCs are tailored for motor-control applications. These include the Motor-Control Pulse Width Modulation (MCPWM), highspeed analog-to-digital converter (ADC), and scalable flash program memory. In addition, the DSP engine of the dsPIC DSC supports the necessary fast mathematical operations required for executing computationally intensive control loops. We will discuss how the dsPIC DSCs can be used to control the motor in a washing machine, using the FOC algorithm. In a washing machine, the dsPIC DSC is the signal controller on the motor control board. The user interface module can be handled by an 8-bit microcontroller (MCU) such as Microchip’s PIC16 or PIC18 families of MCUs. The FOC algorithm can be implemented for a 3 phase induction motor (ACIM) or for a 3-phase Brushless DC (BLDC) motor or for a Permanent Magnet Synchronous Motor (PMSM). PMSM motors are more efficient than ACIM motors, by virtue of their construction. In particular, let us see how the sensorless FOC algorithm works for the PMSM motor in a washing machine. Why use the FOC algorithm? Traditional BLDC motors control methods drive the stator in a sixstep fashion, generating oscillations on the produced torque. In a sixstep control scenario, a pair of windings is energized until the rotor reaches the next position, then the motor is commutated to the next step. Hall sensors are used to determine the rotor position in order to electronically commutate the motor. The advanced sensorless FOC algorithm uses Back EMF generated in the stator winding to determine the rotor position. Inherently, the dynamic response of the six step controls (also called trapezoidal control) is not suitable for washing machine control, because the load is changing dynamically within a wash cycle, and varies with different loads and the selected wash cycle. Further, in a front-load washing machine, the gravitational power works against the motor load, when the load is on the top side of the drum. Only advanced algorithms, such as FOC can handle these dynamic load changes. Theory of FOC The FOC algorithm generates a 3phase voltage as a vector to control the 3-phase stator current. By transforming the physical current into rotational vector using Park and Clarke transforms, (see figures 2 and 3), the torque and flux components become time-invariant—allowing control with conventional techniques such as Proportional & Integral (PI) controllers, as with a DC motor. In brushed DC motors, by construction, the stator flux and rotor flux are kept at 90 degrees to each other, thus generating maximum possible torque from the motor. Using the FOC technique, the motor currents are transformed to 2axis vectors, as seen in a DC motor. The process starts out by measuring the three phase motor currents. In practice, since the instantaneous sum of the three current values will be zero, by measuring only two of the three currents, the value of the third can be determined. Further, there is a reduction in the hardware cost because only two current sensors are required. Clarke Transform The first transform, called the Clarke Transform, moves a 3-axis, 2- Figure 2: Clarke Transfrom International Appliance Manufacturing 2007 49

Table of Contents Feed for the Digital Edition of International Appliance Manufacturing 2007

Contents White Goods- made out of Germany Customer Benefits from Coil Coating Products with “Metal Looks” In Mould Labelling for the Appliance Industry Only Pay for What You Need with Trimmed Concept for Appliance Manufacturers New Lighting Trend in the Oven Innovation in Light and Design- An Introduction Influence of Recycled Material on the Mechanical Performance and Stabilization System of GB355WG Why Choose a Fast Diode Mosfet in a Three-Phase Inverter Topology Providing Six-step Current Commutation Appliance Motor Control Made More Efficient, Cost- Effective Through Sensorless FOC Control Save, Bright and Spotlessly Clean Stainless Steel Strip is Stepping Out with the Launch of Sandvik Decorex New Hot Melt Silicone Sealant Technology Reduces Time, Costs for Appliance Manufacturers IR Touch Controls- The 4th Generation Coil Coating Ensures White Goods at Leading Edge Design Coil Coating Ensures White Goods at Leading Edge Design New material Solutions That Help Satisfy Consumer Wants, Producer Needs and Regulatory Musts for Tomorrow’s Appliances Welcome to the Chinese Century Multibase PPμ Talc Switches and Sensors Rise to the Challenge Development by SKF of Value Added Solutions (VAS) for Washing Machine Applications Silicon Adhesives for Display Cabinet Construction Instantaneous Hot Water for Beverages A Very Small Real Time Scheduler for Both Cost Effective Home Appliance Controllers and Higher Level Firmware Development Dishwasher Circulation Pump Evolution Nucleated PP Opens the Door to Improvements in Design and Productivity of Molded Appliance Articles Energy Saving Solutions for Home Appliances Sensors Sensors Sensors and No Way Back An Integrated Driver for LED Panel Renders the Traditional MCU Obsolete Integrating Hall-effect Magnetic Sensor Technology into Modern Household Appliances High Efficiency, Low Cost BLDC Evaperoator Fan Motor with a Soft Magnetic Composite Stator and Bud TM Controller Household Dishwashers Energy Consumption Reduction- A Success Story Novel fan Design Offers Energy Savings to Refrigeration Market

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