NXP Semiconductors DSP56800E User Manual

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NXP Semiconductors DSP56800E User Manual Manual pdf 32 page image

The GMCLIB_ElimDcBusRip function is used for a correct PWM duty cycle outputcalculation, based on the measured DC-bus voltage. The side effect is the elimination ofthe the DC-bus voltage ripple in the output PWM duty cycle. This function can be usedwith any kind of space vector modulation; it has an additional input - the modulationindex (with respect to the DC-bus voltage).The general equation to calculate the duty cycle is as follows:Equation 22where:• UPWM is the duty cycle output• uFOC is the real FOC voltage• udcbus is the real measured DC-bus voltage• imod is the space vector modulation indexUsing the previous equations, the GMCLIB_ElimDcBusRip function compensates anamplitude of the direct-α and the quadrature-β component of the stator-reference voltagevector, using the formula shown in the following equations:Equation 23Equation 24where:• Uα* is the direct-α duty cycle ratio• Uβ* is the direct-β duty cycle ratio• Uα is the direct-α voltage• Uβ is the quadrature-β voltageIf the fractional arithmetic is used, the FOC and DC-bus voltages have their scales, whichtake place in Equation 22 on page 32; the equation is as follows:GMCLIB_ElimDcBusRipGMCLIB User's Guide, Rev. 2, 10/201532 Freescale Semiconductor, Inc.