Embedded Systems October 2000 Vol13_11

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SPECTRA • which we will call -waler. Therefore, if we add the +water to the -water, we'll get zero. No other waters are involved. If water goes in one end it will come out the othe r. A three-phase system is similar, except we have three bi-direc- tional inputs. With a high frequency PWM we can make fine adjustments to the amount and the angle of the stator flux . If we examine the motor from the stator point of view, we see three-phase current flux angles that change con- stantly. If, however, we assume a fixed position on the rotor, we can see tllat two fluxes must be present in a motor U S Software Knows Why CAD-UL is #1. U S Software knows who to count on when they need a partner for x86 embedded development tools. And it looks like they're not alone. According to VDC, CAD-UL is the number one revenue generator of m edded d ve opm n tools for it to move and produce torque, and that they will be about 90 degrees from one another. One is tile rotor flux, which in a permanent magnet motor, is fixed by the circular magnets on the rotor. The oth er, the stato r flux, is generated by the three-phase windings on the stator. These two flux- es can be mathematically gene rated by two currents, 1" and I(r This separation of cun-ents is a mathematical o pera- tion illustrated by the vector sum in Figure 5. The vector sum of tile flux genera ted by the magnets on the armature and th e flux from the wind- ings on the stato r, result in a third vec- tor often referred to as torquing flux. Recall that we are imagining this picture from a fixed position on the rotor. Here, the values of 1" and I" change very slowly. You will see from the vector diagram in Figure 5 th at on a permanent magnet motor, it is only necessary to manipulate the winding flux to create acceleration, decelera- tion, or a profile, because the flux from the permanent magnets is fixed. This means that on a brushless perma- nen t magnet motor, the f" may be zero. But to control the stator flux , we ~ U S SOFTWARE. , ~ . EMB E DD ~ D EKC ELLE NC E • Real-Time Operating System • Embedded TCP/IP Protocol Suite • Embedded File System • Distributed Computing (800) 356-7097 • C/C++ x86 Compiler Systems • Symbolic Debugging Systems • IDE: CAD-UL Workbench • Code Coverage Tools (877) GO CAD-UL CAD-UL need to generate phase currents; or, you could say, we want to use our power bridge to produce an average voltage across each phase that will gen- erate the proper fllLx in the windings to cause tile motor to turn as we choose. It can be shown (please see tile bibliography) that I" and I" are a result of tile individual phase currents and the position of the rotor as shown here: [] [ ' " 152 OCTOBER 2000 Embedded Systems Programming '. ="3 -sin(O) -sin(O-y) -sin(0 - 2y) , : (1) 2 eos(O) eos(O-y) eos(0- 2y) , 1 This formula is the product of two formulae: eos(y) sin(y) eos( 2 y)li . o sll1(2y) ic '. ] (2) '"1

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