Download Inverters for Variable Frequency Drives Prof. Thomas Jahns Bruce

Inverters for Variable
Frequency Drives
Prof. Thomas Jahns
Bruce Beihoff
May 11, 2016
Dynamics and Control of AC Drives
UW-Madison
WEMPEC
Outline

Introduction

Power Converter/Inverter Classification
Structure

HVAC/ Refrigeration Inverter Applications

Future Inverter Technologies of Importance
to HVAC/ Refrigeration

Conclusions
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Inverters for Variable Frequency Drives
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Voltage-Source PWM Inverters
Multi-Level
Matrix

Voltage-source PWM inverters are the most widely-used
class of ac drives today
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Basic AC Drive Architecture
Electrical
Power
Source
Electrical
Power
Converter
AC
Machine
Modulation and Control
Command
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Examples of AC Drive Power Converters
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PWM Waveform Synthesis
-
PWM is based on the concept of time-varying duty cycle control
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Pulse Width Modulation for VSI Drives

PWM makes it possible to use same inverter switches for
frequency and amplitude control, plus low-harmonic reduction

PWM voltage waveforms ‘saturate’ to 6-step when pulses drop
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Inverters for Variable Frequency Drives
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PWM Synthesis – A, B & C Phases
• Three PWM sequences are
progressively time-shifted
by 120 elec. deg.
• No adjustment of dc link
voltage amplitude is
necessary
– Phase-controlled rectifier can
be replaced by simpler
uncontrolled rectifier
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Inverters for Variable Frequency Drives
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V/Hz Control of PWM VSI-IM Drive
Core of
V/Hz Control

Simple open-loop V/Hz control of PWM VSI-IM drive follows
same basic principles as for 6-step VSI drive
– PWM modulation control is slaved to frequency command
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Inverters for Variable Frequency Drives
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PWM VSI Induction Motor Drives
Advantages
–
No need to provide means to adjust bus voltage
–
Reduced low-frequency current harmonics and torque
ripple
Disadvantages
–
Much higher switching frequency reduces inverter
efficiency
–
High-frequency current harmonics may still cause
noticeable motor losses, requiring machine derating
–
High inverter switch dv/dt’s and di/dt’s can cause damage
to winding insulation or bearings
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Current-Regulated PWM (CRPWM) VSI Drive

Instantaneous phase current waveforms can be regulated by
closing feedback loops using measured phase currents

Provides basis for high-performance ac machine torque control
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Simplified Block Diagram of CRPWM VSI-IM
Drive using FOC
Induction
Machine

By aligning currents appropriately with IM machine flux,
torque and flux amplitudes can be individually controlled
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CRPWM-VSI Induction Motor Drives
Advantages
–
Capable of achieving excellent dynamic torque control
–
Can achieve very low levels of torque ripple
–
Availability of phase currents simplifies protection
Disadvantages
–
Control is more complicated than for basic VSI drive
–
High-performance control typically requires current
sensors plus rotor position or speed feedback
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AC-AC Converter Induction Machine Drives
Multi-Level

Cycloconverters and matrix converters eliminate the
need for an intermediate dc link in the power converter
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Matrix Converter: Direct ac↔ac
• Three-phase ac input: Three line input
• Three-phase output: Three line output
– Requires 3 triple-throw switches
– Each switch capable of turning on and off, plus
blocking voltage & current in both polarities
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Matrix Converter Implementation
Using IGBTs
• Each bilateral switch implemented using 2 IGBT’s and 2 diodes
• Requires total of 18 IGBTs and and 18 diodes
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Matrix Converter Motor Drives
Advantages
–
High input and output power quality using PWM
–
Input and output power factor are independently controlled
–
Inherent 4-quadrant operating capabilities
–
No dc link capacitors
Disadvantages
–
Unavailability of bilateral controlled switch devices requires
high power semiconductor parts count
–
Maximum output voltage as fraction of input is limited
–
Harmonic filters on input lines can be substantial
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Synchronous Machine Drives
Multi-Level

Preferred converters overlap with those of induction machines, but
there are differences
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Open-Loop VSI Synchronous Motor Drive

No rotor position feedback needed for low-performance
applications
–

Damper cage typically needed for improved stability
Constant V/Hz control holds flux ~ constant, just as for IM
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Current-Regulated VSI-SM Drive

Growing popularity of permanent magnet SMs is creating growing
opportunities for CRPWM VSI drives for lower power

“Self-synchronous control” is key to field-oriented control of SM
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HVAC/Refrigeration Inverter Applications

Variable Torque
– Fans
– Pumps
– Centrifugal and Scroll

Constant Torque
–
Reciprocating Compressors
–
Screw Compressors
–
Positive Displacement Pumps
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HVAC/Refrigeration Inverter Applications
Inverter Based VFD have found applications
in every major sub-system
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Inverter Based Systems Entering Market
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The Inverter VFD Value Proposition
HVAC/Refrigeration
Advantages
• Energy savings
• Low motor starting current
• Reduction of thermal and
mechanical stresses on
motors and belts during
starts
• Simple installation
• High power factor
• Lower KVA
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HVAC/ Refrigeration VFD Inverter Challenges
Motor Transient Voltages
Power line Harmonics
Progress vs. Challenges (2006-2016)
•
•
•
Electromagnetic Interfence
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Intrinsic Filtering and Smart switching
have reduced standard drive power line
harmonics below 5% THD
Motor Transient voltages on med/long cables
have been reduced by 50% by better
switching
and filters
EMI/RFI has been reduced by 50 % through
smart layout , grounding, filters, and better
switching
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High Speed VFD Compressors
Multi Piston Reciprocating
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Turbo Compressor
( 15,000-22,000 rpm)
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Future Technologies

Advanced Semiconductor Switches

Advanced Controls

Advanced Power System Integration
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Advanced Semiconductor Switch


Improved Silicon Based Switches
Wide Bandgap Semiconductor Switches
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Power Semiconductor Limits
• Some devices are
pushing Si boundary
• SiC and GaN offer
promise for advances
100M
10M
Thyristors
GTOs
IGCTs
Power (VA)
1M
100K
IGBT
MODULES
BIPOLAR
TRANSISTOR
MODULES
10K
MOSFET
Modules
1K
100
DISCRETE
MOSFET
10
10
100
1K
10K
100K
1M
Operation Frequency (Hz)
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Wide Band Gap Semiconductors
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Advanced Controls

Advanced Micro Controller Chip Sets

Per switch cycle Commutation and Control

Model Predictive Control / Adaptive Control
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Per Switch Cycle Direct Control
Advantages
• Precise control of speed and torque
without position sensors
• Fast dynamic response with superior
stability
• Very high efficiency
• Intrinsic noise cancellation
possibilities…
DIRECT INSTANTANEOUS FORCE CONTROL (DIFC)
(Example)
Disadvantages
• Requires more powerful processor
• More complex control code
DEADBEAT-DIRECT TORQUE CONTROL OF INDUCTION
MACHINES ( Example)
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Advanced Micro Controllers
Advantages
• Cost decreasing at 12% /year
• Control MIPS > 30
• Capable of processing 8
control loops
at 1 us update cycles
Disadvantages
• May still be too expensive
?????
• Control code still complex to
integrate
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Model Predictive Control
Advantages
• Robust under the most non-linear
conditions
• Combines auto-tuning and
commissioning
• Combines stability with optimality
Disadvantages
• Requires more powerful processor
• Requires reasonable model of process
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Advanced Power System Integration

High Temperature Inverters

Standard Cell Power Integration

Integrated Motor Drive – pumps, fans, compressors
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High Temperature Power Electronics
Lighting
HiT Power
Electronics
Solar PV
Motor Drives
Automotive
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>150°C Inverter Operation


SiC Diodes,
MOSFETs
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Stacked
Ceramic
Capacitors
Packaging is key to
achieving reliable
operation up to 200ºC
Si or SiC are options
APEI
Inverters for Variable Frequency Drives
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High-Temperature Motor Drives
50 kW
Cissoid
250°C
175°C
Performance Controls
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Integrated Motor Drives


Controller in separate
module mounted
onto motor
Ratings up to 10 kW
Danfoss

Profiles of power
converters are
shrinking
Danfoss
Rexroth
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Future Integrated Motor Drives
Inverter
Wireless Control
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Integrated Modular Motor Drive
Machine Pole
Power Electronics
Controller
SMC Pole Piece
Back iron
Coil
+
+
Communication
Bus
Module
Controller
Pole face
IMMD
Modular
Pole-Drive
Unit
CPES (UW)
Each modular pole-drive unit performs as an independent
building block in motor drive stator configuration
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Gen 2 IMMD Implementation
• Prototype 10 kW, 6-phase IMMD motor and
drive built for experimental verification
• Each drive unit includes independent controller
for testing fault-tolerant control characteristics
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Gen 3 IMMD Implementation
200 V, 1.2 kW, 100 kHz
• Uses GaN switches in multi-level converter configuration
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Alternative Building DC-Based Architecture
340 VDC Bus
340 / 48 VDC
48 VDC Bus
48VDC
48VD
C
Power electronics can contribute to major efficiency improvements
and new electrical distribution architectures
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Concluding Observations I

Induction machines are the most popular choices for ASDs,
but synchronous machines are widely used at both high
power (>1 MW) and high-performance low-power
applications (PM machines)

PWM provides a powerful means of combining functions of
adjusting frequency, changing amplitude, and suppressing
low-frequency harmonics

DC link drive architectures dominate ASDs, but
AC-AC matrix converters may become more popular in
future if mature bidirectional switches are developed
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Concluding Observations III

VSI (Voltage Source Inverters) have made major in roads
through out the HVAC and Refrigeration applications

Current-regulated VSI inverters are very popular when higher
performance is required
–
Provides basis for field-oriented control
–
These see further use in advanced compressors

High Speed compressors and higher frequency inverters are
coming with advanced inverters

Inverters based on wide bandgap semi-conductors that are
higher frequency and very mechanically tough are beginning to
appear

Integrated Motor Drives are making their second foray into
broader HVAC and Refrigeration applications.
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