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Harmonics Analysis in Control System. Limei Zhao 06/06/03. Origin of Noise. DSP part Fast switching frequency Voltage Source Inverter Thermal noise Dv/Dt effects LPF Thermal loss Motor EM interaction Acoustic interaction. PWM Signal from DSP. Signal after VSI before LPF.

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Presentation Transcript
origin of noise
Origin of Noise
  • DSP part
    • Fast switching frequency
  • Voltage Source Inverter
    • Thermal noise
    • Dv/Dt effects
  • LPF
    • Thermal loss
  • Motor
    • EM interaction
    • Acoustic interaction
dsp part harmonics
DSP Part Harmonics

t Domain

ω Domain

  • Electrical frequency harmonics
    • Space vector pwm algorithm
      • Modulated Signal m(t)= sine wave + 3rd Harmonic
    • Non Linear Load
      • VSI
      • PMSM (oscillations but assume none)
  • Switching Frequency Harmonics
    • Switching function s(m,c)
      • PWM
      • Pulse of same amplitude but different width

1 2 3

Generally, 3rd harmonics is thought unharmful to three phase systems
  • But the results show that 3rd harmonic still need to be considered when designing a filter

The signal is before VSI

vsi harmonics analysis
VSI Harmonics Analysis
  • VSI generated harmonic are of following orders

n = p* k ± 1, where k = 1, 2, 3, …; p is the number of pulse

  • The harmonic currents rms value for 6-pulse

Hn = H1/n

lpf part
LPF Part
  • Power dissipation on filter passive components
  • It is important to find balance value of L or C to get both
  • good LPF and less power dissipation
some useful filter 2 passive sinusoidal filter

Simple and




Limited effectiveness

Line drop


Simple and reliable

For tune frequency: THDI<5%

Increase in the input power factor due to capacitive current


Limited spectrum

Some Useful Filter(2)--- Passive Sinusoidal Filter

L Filter

LC Filter

motor part
Motor Part
  • Power transfer are sources of harmonics
    • Because Magnetic materials are operated very close and in non-linear region
    • The transfer magnetising current will be non-sinusoidal and containing harmonics (mainly 3rd ) even if the applied voltage are sinusoidal
  • Rotating machines are sources of harmonics
    • The winding can never be exactly sinusoidally distributed so that MMF is distroted
    • Coil spanning in 3-phase machine can be used to reduce 5th and 7th harmonics
    • 3-phase machines can block 3rd harmonic current at some extent
    • Harmonics produced are considered negligible compared to those produced by other sources
current voltage to motor
Current & Voltage to Motor

Red is phase to phase voltage ; Green is phase current

@ about 60KRPM with LPF(L=150uH)

the effects of harmonic distortion
The Effects of Harmonic Distortion
  • Thermal stress
    • With strong cool air, motor current are obviously better
    • Heat sink
  • Unstable
  • Insulation stress
    • Especially for new motor’s much high current
  • Load disruption