basics of power inverters

Basics of the Power Inverter

Before We Start q  This webinar will be available at

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q  Q&A at the end of the presentation

q  Hashtag for this webinar: #WindWebinar

Moderator Presenters

Paul Dvorak Windpower Engineering

& Development

John Greulich PSI Repair

Aaron Lawson PSI Repair

Our Livonia Campus

PSI Repair Services, Inc.

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Repair Capabilities

Electronics

Robotics

Motion  Control

Process  Control Instrumentation

Hydraulics

Vacuum  Pumps

Servo  Valves

Ball  Screw Gearboxes

What is an Inverter?

An inverter is a type of power converter that changes direct current (DC) to alternating current (AC).

Types of Power Converters

AC

AC

DC

DC

AC/DC  Rectification

DC/AC  Inverting

DC/DC  Converting AC/AC  Converting

Types of Power Converters

AC

AC

DC

DC

AC/DC  Rectification

DC/AC  Inverting

DC/DC  Converting AC/AC  Converting

Types of Power Converters

AC

AC

DC

DC

AC/DC  Rectification

DC/AC  Inverting

DC/DC  Converting AC/AC  Converting

Types of Power Converters

AC

AC

DC

DC

AC/DC  Rectification

DC/AC  Inverting

DC/DC  Converting AC/AC  Converting

Types of Power Converters

AC

AC

DC

DC

AC/DC  Rectification

DC/AC  Inverting

DC/DC  Converting AC/AC  Converting

Predecessor to Solid State Inverters

Rotary Converter - Converts alternating current (AC) to direct current (DC), or DC to AC power.

Where Are Inverters Used?

•  Renewable Energy •  Electric Vehicles •  Industrial Applications •  Medical

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

Generator   Rec+fier  AC-­‐DC  

DC  Link  Capacitors  

Inverter  DC-­‐AC  

Communica+on  &  Control  Unit  

3  Phase  Transformer  

What Does an Inverter Do?

How Does an Inverter Work?

PWM Waveform

AC Voltage

DC voltage

What is PWM •  PWM: Pulse Width Modulation •  Square wave with a varied duty cycle •  Duty Cycle is the on-time/period

LOWHIAVG VDDVV )1( −+=

period

off-time on-time

DC  Link  Capacitor

Bus  Structure

IGBT Heat  Sink

Main Components of a Wind Inverter System Generator Pad  Mount  

Transformer

Utility  Grid Drive  Electronics

Control  Electronics

Snubber  Capacitor

Types of Generators Asyncronous Generators

Types: Squirrel Cage DFIG

Syncronous Generators Types: Permanent Magnet

Electrically Excited

Wind Applications

Doubly-Fed Asynchronous Generators

•  Around 80% of wind turbines •  Main Disadvantage: Slip ring contacts

Full Power Converter

•  Reasonably priced, efficient converter •  Disadvantages: Increased losses and Harmonics

Bi-Directional Full Power Converter

•  Full power available in low wind conditions

Solar Applications

Basic Photovoltaic Inverter System

•  Maximum Power Point (MPP) Tracker or DC-DC boost converter

String inverter

•  Example: Rooftop photovoltaic systems •  Outputs from 500 W to 5 kW

Multistring inverter

•  Example: Medium sized rooftop or ground-based systems

•  Outputs from 3 kW and 30 kW

Central inverter

•  Example: Large three-phase solar farms

•  Outputs from 60 kW to 1 MW

General Applications

Basic Converter

•  Example: Machine Tools under 15kW •  Not able to recover energy

Bi-Directional Converter

Energy Efficient: energy fed back to the grid

Well Balanced Switching

Goals of a Well Designed Inverter

Long Life Good Thermal

Efficiency

Wide Operating

Temperature Customer

Satisfaction

Fast Fault Detection

DC  Link  Capacitor

s

How Design Affects Inverter Operation

•  Fast Switching •  Cost effective – Typically 30-50% of

inverter cost

IGBTs

•  Low equivalent series inductance (ESL) •  Film vs Aluminum Electrolytic

Snubber  Capacitor

s

Bus  Structure

How Design Affects Inverter Operation

•  Low Stray inductance

•  Poor snubber circuits can increase ringing

Drive  Electronic

s

Control  Electronic

s

How Design Affects Inverter Operation

•  Controls the IGBT •  Short circuit and overvoltage

protection

•  Controls Speed and Duty Cycle

Heat  Sink

How Design Affects Inverter Operation •  Surface flatness ≤ 50µm •  Surface roughness ≤ 10µm

OEM specified screen

Thermal interface material

Thermal Resistance

Minimum Maximum

Thickness of TIM

Thermal Interface Material (TIM)

Thermal Resistance

Minimum Maximum

Thickness of TIM

Thermal Interface Material (TIM)

Thermal Resistance

Minimum Maximum

Thickness of TIM

Thermal Interface Material (TIM)

Thermal Resistance

Minimum Maximum

Thickness of TIM

Thermal Interface Material (TIM)

The Perfect Switch

Fast Turn On Fast Turn Off

No Overshoot or Ringing

Design Trade-offs

Speed

Excessive Voltage Spikes

Safe Operating Zone

Excessive Heat

The Worst Case: Overvoltage Excessive voltage overshoot

Excessive Ringing

V=𝐿𝑑𝑖/𝑑𝑡  1000V IGBT Nominal

1700V IGBT Peak

The Worst Case: Excessive Heat

Very Slow Turn Off

Excessive Heat Generation

Very Slow Turn On

The Real World Switch

Minimal Turn on time

Minimal Turn off Time

Minimal Overshoot Minimal Ringing

Failure Originating from Utility Grid

Grid Faults include: •  Transients •  Power Factor issues •  High grid voltage •  Low grid voltage

Failures

Questions? Paul Dvorak Windpower Engineering & Development pdvorak@wtwhmedia.com Twitter: @Windpower_Eng

John Greulich PSI Repair John.greulich@psi-corp.com Phone: 734.751.5133 Twitter: @psi_repair

Aaron Lawson PSI Repair Alawson.rsi@psi-corp.com Phone: 734.8535427 Twitter: @psi_repair

Thank You q  This webinar will be available at

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