TechKnowledge, LLCsmallwindconference.com/wp-content/uploads/2017/06/2...2017/06/02 · Power Circuits Small Wind Turbine Raw Wild AC Conditioned Wild AC Switching Power Electronics

Advantages and Trade-offs

with Active Rectifiers

for Small Wind Turbines

Lane Woodland

Significant Performance Benefits, but There Are Trade-offs

TechKnowledge, LLC“transforming concepts into solutions”

11-April-2017

Small Wind Energy Harvest

and Delivery to Grid

TechKnowledge, LLC – transforming concepts into solutions…

Mechanical Input Power to Alternator

Based on Swept Area and Blade Design

Electrical Output Power to Inverter

Based on Alternator Design

3-Phase Voltage and Frequency

Proportional to Turbine RPM

1-Phase Voltage, Frequency and Phase

Synchronized to Grid

Electrical Input Power from Turbine

Based on Turbine Design and Wire Run Length

Electrical Output Power to Grid

Based on Inverter Design

Typical Small Wind Power Train(Factors Affecting Efficiency and Energy

Production)


Location

Site Assessment

Tower Height

Turbine Blade Design

Swept Area

Airfoil Design

Fixed or Variable Pitch

Alternator Design

Rotor Design

Geometry (Pancake or Sausage)

Surface or Interior Magnet Placement

Magnet Material and Size

Number of Poles

Stator Magnetic Design

Number of phases

Laminated Steel or Iron-less flux path

Stator Winding Design

Rated Voltage vs. Current

Distributed or Concentrated Windings

Wire Run Loss from Turbine to Inverter

Tower Height

Distance from Tower to Inverter

Wire Gauge

Fused Disconnect Switch

Rectifier Design

Full-wave Diode Bridge

Controlled SCR Bridge Rectifier

Sine-wave “Synchronous” Rectifier

Boost Converter Design (in Many Cases)

Switching and Conduction Loss

Inductor and Capacitor Filter Loss

Inverter Design

Switching Loss and Conduction Loss


Power Topology and Control Algorithms

Utility Panel and Installation

Fuses/Breaker Heating Loss

Wiring Voltage Drop Loss


Production)


Location

Site Assessment

Tower Height


Swept Area

Airfoil Design


Alternator Design

Rotor Design




Number of Poles


Number of phases






Tower Height


Wire Gauge


Rectifier Design







Inverter Design








Production)


Location

Site Assessment

Tower Height


Swept Area

Airfoil Design


Alternator Design

Rotor Design




Number of Poles


Number of phases






Tower Height


Wire Gauge


Rectifier Design







Inverter Design








Production)


Location

Site Assessment

Tower Height


Swept Area

Airfoil Design


Alternator Design

Rotor Design




Number of Poles


Number of phases






Tower Height


Wire Gauge


Rectifier Design







Inverter Design







Conventional Grid-tie Inverter

with FWB Diode Rectifier and Boost

Converter


Grid-tie Inverter

Control and Support Circuits

Power Circuits

Small

Wind

Turbine

Raw

Wild AC

Conditioned

Wild AC

Variable

DC

Switching

Power

Electronics

Input Filter

&

Lightning

Protection

Utility

Service

Panel

To

Grid

FWB

Diode

Rectifier

Control Electronics

&

Software

Logic

Power

Supply

Boost

Converter

Regulated

HVDC

Output

Filter

&

Transient

Protection

PWM AC Clean AC

Aux

I/OComm.

Sub-

sytstem

Control

Fan(s)

FWB Diode Rectifier with Boost

Converter


Wild

AC

From

Turbine

Regulated

High

Voltage

DC

To

Inverter

Stage

Variable

DC

Voltage

FWB Diode Rectifier Boost Converter

Improved Grid-tie Inverter

with Active Rectifier


Grid-tie Inverter

Control and Support Circuits

Power Circuits

Small

Wind

Turbine

Raw

Wild AC

Conditioned

Wild AC

Switching

Power

Electronics

Input Filter

&

Lightning

Protection

Utility

Service

Panel

To

Grid

Active

Rectifier

Control Electronics

&

Software

Logic

Power

Supply

Regulated

HVDC

Output

Filter

&

Transient

Protection

PWM AC Clean AC

Aux

I/OComm.

Sub-

sytstem

Control

Fan(s)

Active Rectifier Includes Boost Function


Wild

AC

From

Turbine

Regulated

High

Voltage

DC

To

Inverter

Stage

Active Rectifier

Predominant 3-Phase PM Alternator

Types


Brushless DC (BLDC) Alternator

Trapezoidal Voltage Waveforms

Typically Concentrated Stator

Windings

Commonly used with Diode

Rectifiers

Good Rectified DC Output Voltage

AC Alternator

Sinusoidal Voltage Waveforms

Typically Distributed Stator

Windings

Common for Diesel Gen-sets

True AC Output Voltage

Simplified 3PH Alternator Simulation Model

(configurable for AC or BLDC machines)


Alternator

Mechanical

Input

Alternator

Electrical

Output

Simulations Configured for Ginlong

Alternator


To be used on upcoming Weaver

Wind Energy W15 Turbine

AC Sine Wave Alternator

Simulation with FWB Diode Rectifier

Simulation with Active Rectifier

AC Alternator Line-Line Voltage

and FWB Diode Rectified Voltage (no load)


Valley at rectified voltage crossing is 0.866 of peak voltage

AC Alternator Line-Line Voltage and

Current

with FWB Diode Rectifier under 15kW Load


Line voltage is clipped, due to bus capacitor and diode clamping of phase voltages

Leads to double hump phase current pulses due to sine wave EMF into DC bus capacitance

AC Alternator Rectified DC Voltage and

Power

with FWB Diode Rectifier Under 15kW

Load


Pretty good rectified DC output voltage (625VDC under 15kW load with 6,000uF

Need high capacitance for low ripple voltage

AC Alternator Phase Currents and Torque


Load


Extreme torque ripple due to deep current valleys (double humps) 1400Nm pk-pk @ 85Hz causes severe vibration and significant audible

noise!

AC Alternator Power and Efficiency


Load


Extreme power fluctuation ~19kW pk-pk (about 6,700W rms@85Hz)!!!

Efficiency about 85% without boost function (likely about 80% with boost)

AC Alternator Line-Line Voltage with Active

Rectifier

(open circuit and 15kW load)


Alternator 3-phase voltage waveforms are sine waves (no notches or clipping) Requires properly designed EMI filter to minimize PWM noise

AC Alternator Line-Line Voltage and

Current

with Active Rectifier under 15kW Load


Alternator 3-phase currents are sine waves with near zero

harmonics!!!

AC Alternator Line-Neutral Voltage and

Current

with Active Rectifier under 15kW Load


Alternator phase currents are in phase with phase voltages (L-N) Operating at Unity Power Factor for maximum efficiency (i.e. cos(0) =

1)

AC Alternator Phase Currents and Torque

with Active Rectifier Under 15kW Load


Near zero torque ripple due to sine wave current Negligible rectifier induced vibration or audible noise!

Constant Torque from Simple Trig

Identity


𝑥 = 𝑎 cos 𝜃

𝑦 = 𝑎 sin(𝜃)

𝑥2 + 𝑦2 = 𝑎2

sin2(𝜃) + cos2(𝜃) = 1


Identity




𝑥2 + 𝑦2 = 𝑎2

sin2(𝜃) + cos2(𝜃) = 1

cos(𝜃) = sin(𝜃-90º)

sin2(𝜃) + sin2(𝜃−90º) = 1


Identity




𝑥2 + 𝑦2 = 𝑎2

sin2(𝜃) + cos2(𝜃) = 1

cos(𝜃) = sin(𝜃-90º)

sin2(𝜃) + sin2(𝜃−90º) = 1

sin2(𝜃) + sin2(𝜃−120º) + sin2(𝜃−240º) = 1.5 (which is a

constant)

AC Alternator Rectified DC Output Voltage

and Power with Active Rectifier Under

15kW Load


Excellent rectified DC output voltage under 15kW load with only 330uF

Lower minimum required capacitance allows use of longer life film capacitors, rather than electrolytics

Active rectifier boosts DC output voltage to 860VDC or higher if desired

AC Alternator Power and Efficiency

with Active Rectifier Under 15kW Load


Very smooth mechanical load on turbine!!!

No wild vibration or audible noise due to rectifier

Efficiency about 88% (with inherent boost)

Comparison of Rectifier Types


Performance Metric BLDC Alternator

with FWB Diode

Rectifier

AC Alternator

with FWB Diode

Rectifier

AC Alternator

with Active Rectifier

Efficiency (alt + rect)

(alt + rect + boost)

90% no boost,

~85% w/boost

85% no boost,

~80% w/boost

n/a

88% w/boost

DC Voltage Boost

Capability

Extra power conversion

stage (est. 5% eff loss)

Extra power conversion

stage (est. 5% eff loss)

Included

Torque Ripple (vibration) 400Nm pk-pk

(33% of 1,200Nm)

1,400Nm pk-pk

(117% of 1,200Nm)

Near zero

Audible Power 5.5kW pk-pk

~1.9kW rms

19kW pk-pk

~6.7kW rms

Near zero

Min. DC Bus

Capacitance

1,000uF (doable with

film)

6,000uF (high for film

caps)

300uF (easy with film

caps)

EMI Filter Requirement Minimal Minimal Substantial

Cost without Boost Low to mid hundreds

$$$

Low to mid hundreds

$$$

n/a

Cost with Boost mid hundreds to low k$ mid hundreds low k$ Low to mid k$

Summary and Conclusions


FWB Diode Rectifiers

Very simple and reliable and have proven the test of time

Very low cost

Very efficient unto themselves, but they reduce alternator efficiency

Low EMI signature

May require separate DC-DC boost converter for higher DC bus

voltage

Which adds cost, adds to EMI, and can reduce reliability

Negates efficiency benefit of FWB diode rectifier alone

Cause significant to severe vibration and audible noise

Worse with AC sine wave alternators, than with BLDC alternators

Summary and Conclusions


Active Sine Wave Rectifiers

Technology based on VFD’s, and is not new

Includes DC voltage boost function

3-8% efficient improvement over FWB diode rectifier with boost

converter

Eliminates primary source of vibration and audible noise

May extend turbine life with less wear and tear from vibration

Allows for use of long life film capacitors with higher voltage ratings

Requires properly designed input filter to minimize EMI

Adds significant incremental cost, but likely less than cost of a full

VFD

Q&A


Thank you for your time!

Lane Woodland

President

TechKnowledge, LLC

15366 W Sunrise Circle

Eden Prairie, MN 55347

612-709-9038

[email protected]

www.techusout.net

mailto:[email protected]

Backup Slides


BLDC Alternator Line-Line Voltage

and FWB Diode Rectified Voltage (no load)


Very good rectified DC output with no voltage ripple

BLDC Alternator Line-Line Voltage and

Current

with FWB Diode Rectifier under 15kW Load


Line voltage notches due to inductance and extended diode conduction

Phase current distortion due to alternator inductance

BLDC Alternator Rectified DC Voltage and

Power

with FWB Diode Rectifier Under 15kW Load


Pretty good rectified DC output voltage @660V under 15kW load with 1,000uF

Easy to improve ripple with more capacitance

BLDC Alternator Phase Currents and

Torque


Load


Significant torque ripple due to current distortion 400Nm pk-pk @ 85Hz causes significant vibration and audible noise!

BLDC Alternator Power and Efficiency


Load


Significant power fluctuation ~5.5kW pk-pk (about 1,940W rms@85Hz)

Pretty good efficiency (about 90% without boost function)

Documents

TechKnowledge, LLCsmallwindconference.com/wp-content/uploads/2017/06/2...2017/06/02 · Power Circuits Small Wind Turbine Raw Wild AC Conditioned Wild AC Switching Power Electronics