søren poulsen, spo@oersted.dtu.dk Ørsted·dtu, automation technical university of denmark norpie...

NORPIE 2004 1

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Hysteresis Controller with constant switching frequency

Søren Poulsen

Ph.D. Student

Ørsted·DTU

Technical University of Denmark

spo@oersted.dtu.dk

Michael A. E. Andersen

Professor

Ørsted·DTU

Technical University of Denmark

ma@oersted.dtu.dk

NORPIE 2004 2

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Standard hysteresis controllers

• Current or voltage mode

NORPIE 2004 3

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Band pass current mode

• Current loop with bandpass function– Only control of output filter resonance

NORPIE 2004 4

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Hysteresis controllers• Benefits

– Sawtooth shaped carrier• Linear modulation

– Modulator includes power stage• Error reduction

– Open loop bandwidth = fs

• Concerns– Switching frequency dependent on modulation

index: 2,0 1s sf M f M

NORPIE 2004 5

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Constant switching frequency hysteresis modulators

• Variable FW gain– Hysteresis clamp– Variable gain amp

NORPIE 2004 6

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Constant switching frequency hysteresis controller

• Hysteresis controller with additional comparator and integrator

NORPIE 2004 7

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Carrier distortion

• Control output WILL have HF content– Adds to the carrier

– Adding control decreases performance of inner modulator loop

• Shaping inner/outer loops in a way so control output inherently adds to carrier constructively

NORPIE 2004 8

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Shaping modulator and feedback

NORPIE 2004 9

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Constant switching frequency prototype

• Very low cost implementation

• fs,0 150kHz• Closed loop bandwidth = 30kHz• Modulator loop propagation delay: 325ns

NORPIE 2004 10

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Constant switching frequency prototype

• 2-layer PCB

• +/- 40V supply

NORPIE 2004 11

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Prototype carriers

NORPIE 2004 12

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Prototype switching frequency, M=0.8, 10Hz, 100Hz, 1kHz

NORPIE 2004 13

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Prototype switching frequency, DC

NORPIE 2004 14

Søren Poulsen, spo@oersted.dtu.dk

Ørsted·DTU, AutomationTechnical University of Denmark

Conclusion• Almost constant switching frequency

for low frequency modulation• Very simple modulator design• Low cost implementation possible• Additional feedback without distorting

the carrier is possible• ”Perfect” first carrier signal despite

only passive modulator loop