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FPGA high efficiency, low noise pulse frequency space vector modulation--Part I

Dr. Giulio Corradi, Xilinx Industrial, Scientific & Medical Group (ISM) Germany -October 04, 2012

Power modulation is crucial in motor control to ensure high efficiency, fast response time, low ripple torque, low harmonic generation and low acoustic noise. Pulse Width Modulation (PWM) is typically used in continuous methods like Space Vector Modulation (SVM) and discontinuous methods such as Flat-Top Modulation (FTM) exhibit harmonics and require complex mechanisms to mitigate such harmonics. The properties of different modulation methods like Pulse Frequency Modulation (PFM) or Pulse Density Modulation (PDM) can be used advantageously for standalone, or in combination with PWM, to push and spread the noise out of the band of interest, properly shaping the power signal to reduce the acoustic noise, harmonics ripple, distortion, switching losses and the overall modulator complexity.

PFM is clearly beneficial at a modulation index higher than 0.4, thus the realization of a versatile power modulator allowing on-the-fly switching between a space vector PWM and a space vector PFM, coupled with a fast current loop, achieves less switching, a finer torque ripple control and satisfies many motor control applications. This article describes the PWM- PFM versatile modulator, along with its advantages and practical results when applied to Brushless DC (BLDC) motors, Permanent Magnet Synchronous (PMSM) motors and Stepper motors as part of a set of functional motor control libraries implemented for the latest generation of 7 Series All Programmable FPGAs.

Power inverters are at the heart of most power control systems or electrical drives, where digital modulation is used to transfer commanded voltages or currents. Controllable magnitude and frequency are used as a series of high frequency pulses to loads or motors. Power semiconductor switches receive low voltage pulses and transform them into power pulses adequate for the load or motor. The load behaves, in general, as an integrator reconstructing the magnitude and frequency of the original commanded signal.

Real power semiconductor devices, such as MOSFETs, IGBTs, GTOs, etc., experience im

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