Integrated Common and Differential Mode Filters with Active Damping for Active Front End Motor ...

147 Pages·2011·4.71 MB·English

Integrated Common and Differential
Mode Filters with Active Damping for
Active Front End Motor Drives
A Thesis
Submitted for the Degree of
Master of Science
in the Faculty of Engineering
By
Anirudh Acharya B
Department of Electrical Engineering
Indian Institute of Science
Bangalore - 560 012
India
January 2011
Acknowledgements
Any accomplishment in any walk of life is a collective effort - some contribute directly and
few indirectly. Hence I would like to mention a few who influenced, enthused, guided and
helped me to bring out this thesis.
At the outset, I would like to record my gratitude to my advisor Dr. Vinod John for
acceptingmeasastudentofPowerElectronicsGroup. Hisenthusiasm, guidanceandconcern
throughout my research have made my stay at IISc a memorable and cherishable moment
in my life. Apart from being a great teacher and a guide, his student centric approach with
grace and humility has been a great inspiration to me.
I owe my deepest gratitude to Dr. V. Ramanarayanan for sharing his wisdom inside and
outside the class room. His thought provoking ideas and simplistic approaches to complex
problems have influenced my research in a great way. I am grateful to (late) Dr. V.T.
Ranganathan for his lectures in Electric Drives and for his advice during my research. His
ideas, humble nature and simplicity have been a true inspiration. I am thankful to Dr. G.
Narayanan for his support and encouragement from initial to final level of my research. I
am grateful for all the guidance and concern he has showed towards me during my research.
I am thankful to Dr. G. K. Purushothama (MCE, Hassan), for his constant encourage-
ment and advice to pursue higher studies.
I am indebted to all friends in Power Electronics Group for their support, stimulating
discussions and valuable inputs.
I am thankful to Mr. Ravi, Mr. Ramachandran and the other workshop staff for their
help in building my hardware and Mrs. Silvi Jose for the support extended in procuring
components. I also extend my thanks to Mr. D. M. Channe Gowda and his team at EE
offce for the smooth conduct of administrative activities.
I am thankful to my former colleagues of Mindtree for their encouragement and support
for pursuing higher studies.
This thesis would not have been possible without the continuous support of my family
for which I remain thankful. I am indebted to all who directly, indirectly helped me in this
accomplishment.
i
ii Acknowledgements
Abstract
IGBT based power converters acts as front end in the present day Adjustable Speed Drive
(ASD). This offers many advantages and makes regenerative action possible. PWM rectifier
operation produces electrically noisy DC bus on common mode basis. This results in higher
ground current as compared to three phase diode bridge rectifier. Due to fast turn-ON and
turn-OFFtimeofIGBT,theinverteroutputvoltagedv/dtishighduringswitchingtransients
and voltage waveform is rich in harmonics. As a result, in applications involving long cable
the motor terminal voltage during the switching transient is as high as twice the applied
voltage. This voltage stress reduces the life of insulation in motors. The high dv/dt output
voltage applied at the motor terminal excites the parasitic capacitive coupling resulting in
increased ground currents and causes Electric Discharge Machining (EDM) which reduces
the life of motor bearings. The common mode voltage due to PWM rectifier and the inverter
appear at the motor terminals exacerbating these problems.
The common mode voltage due to PWM inverter with AFE converter is analyzed. An
integrated approach for filter design is proposed wherein the adverse effects due to common
mode voltage of both AFE converter and the inverter is addressed. The proposed topol-
ogy addresses the problems of common mode voltage, common mode current and voltage
doubling due to ASD. The design procedure for proposed filter topology is discussed with
experimental results that validate the effectiveness of the filter.
Inclusion of such higher order filter in the converter topology leads to problems such
as resonance. Passive methods are investigated for damping the line resonance due to LCL
filter and common mode resonance due to common mode filter. The need for active damping
technique for resonance due to common mode filter is presented. State space based damping
technique is proposed to effectively damp the resonance due to line filter and the common
mode filter. Experimental results are presented that validate the effectiveness of active
damping both on the line basis (differential mode) and line to ground basis (common mode)
of the filter.
iii
iv Abstract
Contents
Acknowledgements i
Abstract iii
List of Tables viii
List of Figures ix
1 Introduction 1
1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Voltage Doubling at Motor Terminal . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Effect of High Frequency Common Mode Voltage on Motor . . . . . . . . . . 7
1.4 Common Mode Voltage due to Power Converter . . . . . . . . . . . . . . . . 8
1.5 Mitigation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.6 Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.6.1 Passive Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.6.1.1 Output Reactor . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6.1.2 Common Mode Filter . . . . . . . . . . . . . . . . . . . . . 13
1.6.1.3 Sine Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6.1.4 Clamp Filters . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.6.2 Active Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.7 Other Mitigation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.7.1 Increasing Insulation Grade . . . . . . . . . . . . . . . . . . . . . . . 17
1.7.2 Insulated Bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.7.3 Grounding Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.7.4 Conductive Lubricant . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.7.5 Electro-statically Shielded Motor . . . . . . . . . . . . . . . . . . . . 18
1.7.6 ASD Carrier Setting and PWM Techniques . . . . . . . . . . . . . . . 18
1.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
v
vi Contents
2 Filter Design 21
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 High Frequency Behavior of Induction Motor . . . . . . . . . . . . . . . . . . 21
2.2.1 HF behavior of IM on Differential Mode . . . . . . . . . . . . . . . . 24
2.2.2 HF behavior of IM on Common Mode . . . . . . . . . . . . . . . . . 28
2.3 Filter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.1 Filter Design Objectives . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.1.1 Design Objectives for Motor Filter . . . . . . . . . . . . . . 31
2.3.1.2 Design Objectives For Common Mode DC Bus Filter . . . . 32
2.4 Principle and Design of dv/dt Filter . . . . . . . . . . . . . . . . . . . . . . . 34
2.4.1 Working of dv/dt Filter . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4.2 Design of dv/dt Filter . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4.2.1 Design of Snubber Circuit . . . . . . . . . . . . . . . . . . . 41
2.5 Common Mode Circuit of AFE Converter . . . . . . . . . . . . . . . . . . . 45
2.6 Design of Common Mode Filter for AFE Converter . . . . . . . . . . . . . . 48
2.6.1 Selection of Filter Capacitor C and C . . . . . . . . . . . . . . . 49
y Mg
2.6.1.1 Common Mode Circuit of Proposed Topology . . . . . . . . 53
2.7 Design Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3 Active Damping 61
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.2 Transfer Function Analysis of LCL Filter . . . . . . . . . . . . . . . . . . . . 61
3.3 Passive Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.3.1 Differential Mode Damping . . . . . . . . . . . . . . . . . . . . . . . 62
3.3.2 Common Mode Damping . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.4 State Space Representation . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.4.1 LCL Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.4.2 Common Mode Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.5 Active Damping Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.5.1 State Space Control Law . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.5.2 Control Gain Formula . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.5.2.1 LCL Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.5.2.2 CM Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.5.2.3 Sampling Technique . . . . . . . . . . . . . . . . . . . . . . 75
3.6 Analysis in Discrete Time Domain . . . . . . . . . . . . . . . . . . . . . . . . 76
3.6.1 Discrete Time Representation . . . . . . . . . . . . . . . . . . . . . . 76
Contents vii
3.6.2 Closed Form Expression for Φ and Γ . . . . . . . . . . . . . . . . . . 76
3.6.2.1 Expressing Φ and Γ in terms of Filter Parameters . . . . . . 78
3.7 Reduced order estimator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.8 Design Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
3.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4 Experimental Results 85
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.2 Experimental Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.3 Voltage Doubling at Motor Terminals . . . . . . . . . . . . . . . . . . . . . . 86
4.4 Mitigation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.4.1 L filter at Inverter Terminals . . . . . . . . . . . . . . . . . . . . . . . 87
4.4.2 dv/dt Filter at Inverter Terminals . . . . . . . . . . . . . . . . . . . . 87
4.4.2.1 Working of dv/dt Filter . . . . . . . . . . . . . . . . . . . . 89
4.4.2.2 Effectiveness of dv/dt Filter . . . . . . . . . . . . . . . . . . 93
4.5 Common Mode DC Bus Filter . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.5.1 Traditional Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.5.2 Proposed Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.6 CM Voltage at Motor Terminals . . . . . . . . . . . . . . . . . . . . . . . . . 102
4.7 Active Damping using State Space Method . . . . . . . . . . . . . . . . . . . 106
4.7.1 Effect of Moving Average Filter . . . . . . . . . . . . . . . . . . . . . 106
4.7.2 Resonance Damping due to LCL filter . . . . . . . . . . . . . . . . . 106
4.7.3 Resonance Damping due to CM Filter . . . . . . . . . . . . . . . . . 108
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5 Conclusion 113
5.1 Summary of Present Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.2 Suggestions for Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
A Per Unit System 117
B Guideline from NEMA MG Part 31 121
C Experimental Setup 123
References 127
List of Tables
1.1 The switching states, pole voltages and common mode voltage magnitude . . 10
2.1 Net impedance of the winding for different DM configurations with identical
winding assumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.2 Thebehaviorofmotorwith100mlongcableandparasiticcapacitancebetween
theturnsobtainedfordifferentialmodeconfigurationforYconnectedwinding,
the leakage inductance is obtained using no-load and blocked rotor tests . . . 28
2.3 Design constraints and governing design variable for dv/dt filter . . . . . . . 36
2.4 Base Value used for calculations ActualValue = PerUnit×BaseValue . . . 57
2.5 Parameters for Filter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.6 Designed value of filter parameter . . . . . . . . . . . . . . . . . . . . . . . . 58
3.1 Value of α and α for different sampling time . . . . . . . . . . . . . . . . . 82
1 2
3.2 Value of Φ and Γ for different sampling time . . . . . . . . . . . . . . . . . . 82
3.3 Values of gain matrix coefficients . . . . . . . . . . . . . . . . . . . . . . . . 83
4.1 Reference to different experimental configuration and results . . . . . . . . . 85
4.2 Converter parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.3 The ground current, inverter output voltage dv/dt, voltage between neutral
point M to ground V with and without dv/dt filter and CM bus filter. . . . 111
Mg
C.1 Controller Parameter for system ratings indicated in Table. 4.2 . . . . . . . . 124
viii
List of Figures
1.1 The common mode and differential mode voltages and currents in a power
circuit with motor load connected. . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 The characteristic impedance of cable and load with source. . . . . . . . . . 4
1.3 Motor cross-section showing shaft voltage and circulating current. . . . . . . 7
1.4 Parasitic capacitor associated with the motor. . . . . . . . . . . . . . . . . . 8
1.5 The inverter with diode bridge rectifier front end. . . . . . . . . . . . . . . . 9
1.6 Waveforms illustrating (a) CMV due to drive inverter alone and (b) resulting
CMC due to presence of parasitic capacitance. (c) CMV due to AFE rectifier
switching at higher frequency than inverter (d) CMV due to combined effect
ofinverterandAFErectifier(e)CMCwithAFErectifierASDduetopresence
of parasitic capacitance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.7 dv/dt reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.8 Sine filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.9 Basic sine filter with neutral point connected to DC bus mid-point O . . . . 15
1.10 Basic sine filter with neutral point connected to DC bus positive and negative
rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.11 dv/dt filter topology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.12 A variant of dv/dt filter topology. . . . . . . . . . . . . . . . . . . . . . . . . 16
1.13 The common mode voltage at motor neutral due to AZSPWM1 . . . . . . . 19
2.1 Three phase Y-connected stator winding with parasitic capacitance. . . . . . 22
2.2 (a) Turn-turn parasitic capacitance associated with the single winding (b)
turn-turn, turn- ground parasitic capacitance associated with the single winding 22
2.3 Impedance plot for Y connected DM arrangement of stator windings. . . . . 24
2.4 Impedance plot for Y connected CM arrangement of stator windings. . . . . 26
2.5 Differential Mode test set up for obtaining the impedance plot (a)∆ connected
(b) Y connected. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
ix