Harmonics Analysis in Control System

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# Harmonics Analysis in Control System - PowerPoint PPT Presentation

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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### 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
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

• 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 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
• 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

Simple and

Reliable

Inexpensive

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
• 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

Red is phase to phase voltage ; Green is phase current

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

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