InductionHeater: Difference between revisions

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   {{Project
   {{Project
   |Name=InductionHeater
   |Name=InductionHeater
  |Picture=Hqdefault.jpg
   |Status=In progress
   |Status=In progress
   |Contact= smeding, gori
   |Contact= smeding
   }}
   }}


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* [https://www.youtube.com/watch?v=l7fArOvXhQY https://www.youtube.com/watch?v=l7fArOvXhQY]
* [https://www.youtube.com/watch?v=l7fArOvXhQY https://www.youtube.com/watch?v=l7fArOvXhQY]


==Specs==
== System design ==
* Input power: 3.5kVA, standard single-phase mains
Induction heating works by applying a high-frequency magnetic field to the (conductive) workpiece being heated. Because of the [https://en.wikipedia.org/wiki/Skin_effect skin effect], conduction at these frequencies only occurs in a thin layer on the outside of the workpiece. This acts like the secondary winding of a transformer, allowing current to flow and heating the workpiece through resistive heating.
* Frequency: 10 - 100kHz


==Inverter circuit==
The design consists of the following parts:
The basic power system looks as follows:
* The power stage rectifies mains voltage, which is then chopped into a high-frequency 'modified square wave' with variable duty cycle and frequency.
* The coupling transformer transforms the relatively high-voltage, low-current square wave into a lower-voltage, high-current one, to ease the requirements on the work coil.
* The work coil is where the workpiece is placed to be heated.
* The controller monitors relevant currents and voltages, and generates the waveforms that drive the power stage transistors.


[[File:Induction_heater_system.png|800px]]
=== Specs ===
* Input power: Standard single-phase mains: 230V RMS, 16A max ⇒ 3.5kVA
* Frequency: 10 kHz - 100 kHz
* 500A absolute maximum current in work coil
* 'Modified square wave' control: variable frequency and duty cycle


230V mains input is rectified, then filtered slightly and chopped up into a variable-frequency square wave (or modified sine wave) using an H-bridge made of IGBTs. This is fed into a coupling transformer, which turns this high voltage, (relatively) low-current waveform into a higher-current, lower-voltage one more suitable for the system. This is connected to a series-resonant circuit comprised of the heating coil and a tank capacitor.
=== Controller ===
The controller is based around a [http://www.st.com/content/st_com/en/products/microcontrollers/stm32-32-bit-arm-cortex-mcus/stm32f3-series/stm32f334.html STM32F334] ARM microcontroller. Its job is to generate the drive waveforms for the power stage, and display system status, based on measuring the relevant voltages and currents.


The resonant frequency changes depending on workpiece geometry, coil geometry, workpiece temperature, etc. etc. so this needs to be tracked by a controller.
=== Power stage ===
[[File:Induction_heater_power_stage_schematic.png|1280px|The power stage schematic.]]


The secondary side of the transformer dissipates a lot of power (there are potentially hundreds of ampères flowing there, so fairly large ohmic losses) and will need to be water-cooled to prevent it from getting too hot.
Shown above is the schematic for the power stage. Mains voltage enters on the top left, where it is rectified and filtered to get approximately 325 V DC. Then, four IGBTs (IGBT1H, -1L, -2H, and -2L) form an H-bridge that generates the 10-100 kHz 'modified square wave' for the transformer.


== BOM ==
The IGBTs are driven via gate-drive transformers (GDT1 and GDT2) so that the control circuitry can be isolated from the high-voltage side. These transformers in turn are driven by high-current MOSFET drivers (IC1H, -1L, -2H, and -2L), which receive their signals from the controller.
Some of the components have already been scrounged together. Thanks to benadski for acquiring an induction cooktop that contained many useful parts!


{|class="wikitable"
[[File:Induction_heater_power_stage_board_layout.png|512px|The power stage board layout.]]
!Component
[[File:Induction_heater_power_stage_board_assembled.jpg|768px|The assembled power stage board.]]
!Cost
 
!Comments
=== Coupling transformer ===
|-
The coupling transformer converts the high-voltage low-current chopped mains waveform to low voltage and high current for the work coil. Using a separate coupling transformer relaxes the requirements on the workpiece coil, so it can be adapted more easily to the workpiece being heated.
|Bridge rectifier
 
|
It'll be made from four stacked [https://www.aliexpress.com/item/Dark-Gray-Power-Transformers-Ferrite-Toroid-Cores-100mm-x-60mm-x-15mm/689128147.html 100 × 60 × 15 mm ferrite cores] (to provide enough core cross-sectional area for the magnetic field). The primary will consist of 60 turns of thick litz wire, and the secondary will be 2 turns of 15mm OD copper tubing, giving a winding ratio of 30:1.
|Salvaged from cooktop
|-
|inverter IGBTs
|
|Salvaged from cooktop
|-
|Tank capacitors
|
|Salvaged from cooktop
|-
|DC link filter capacitor
|
|Salvaged from cooktop
|-
|Gate drive transformers
|
|Salvaged from cooktop
|-
|Coupling transformer core(s)
|€42
|http://www.aliexpress.com/item/100mm-x-65mm-x-20mm-Ferrite-Rings-Toroid-for-Filters-Coils/879528762.html, we need 3 of these for enough core area
|-
|Litz wire for transformer primary
|
|Salvaged from cooktop
|-
|Copper tubing, 15mm OD * 5m
|€30
|Conservative estimate from hardware store -- can probably do better. Will need more than 5m for larger work coil.
|-
|Copper pipe compression couplings 15mm * 2
|€12
|Can probably do better
|-
|Water cooling pump
|€5
|Cheap brushless water pumps abound on eBay; e.g. http://www.ebay.com/itm/321431156285
|-
|Water cooling connections
|?
|Need to find best solution
|-
|Water cooling radiator
|?
|Car engine radiator goes €10 - €20 on Marktplaats. Possibly from scrapyard?
|-
|Gate driver *4
|€5
|e.g. http://nl.farnell.com/microchip/tc4420coa/ic-driver-mosfet-6a-smd-soic8/dp/1292283
|-
|Control electronics
|€10
|Microcontroller, displays, assorted resistors&capacitors
|-
|'''Total'''
|€104
|}


== Pledges ==
== Pledges ==
Line 100: Line 51:
* [[Flok]]: 10 euro
* [[Flok]]: 10 euro
* Walter: 50 евра
* Walter: 50 евра
* FooBar: €20
* FooBar: €20 cash betaald
* [[bertrik]]: €10
* [[bertrik]]: €10
* Semafoor: €20 (more if the project is better defined)
* Semafoor: €20  
* [[Morphje]]: EUR 10 (and driving to the hardware store if needed)
* [[Morphje]]: EUR 10 (and driving to the hardware store once)


Total pledges: €160
Total pledges: €170

Latest revision as of 11:49, 1 October 2016

Project InductionHeater
Hqdefault.jpg
Status In progress
Contact smeding
Last Update 2016-10-01

We're working on an induction heater that can be used to heat anything conductive to high temperatures. The plan is to try to use it for forging steel and melting aluminum.

Here are some examples of what a device like this is capable of:

System design

Induction heating works by applying a high-frequency magnetic field to the (conductive) workpiece being heated. Because of the skin effect, conduction at these frequencies only occurs in a thin layer on the outside of the workpiece. This acts like the secondary winding of a transformer, allowing current to flow and heating the workpiece through resistive heating.

The design consists of the following parts:

  • The power stage rectifies mains voltage, which is then chopped into a high-frequency 'modified square wave' with variable duty cycle and frequency.
  • The coupling transformer transforms the relatively high-voltage, low-current square wave into a lower-voltage, high-current one, to ease the requirements on the work coil.
  • The work coil is where the workpiece is placed to be heated.
  • The controller monitors relevant currents and voltages, and generates the waveforms that drive the power stage transistors.

Specs

  • Input power: Standard single-phase mains: 230V RMS, 16A max ⇒ 3.5kVA
  • Frequency: 10 kHz - 100 kHz
  • 500A absolute maximum current in work coil
  • 'Modified square wave' control: variable frequency and duty cycle

Controller

The controller is based around a STM32F334 ARM microcontroller. Its job is to generate the drive waveforms for the power stage, and display system status, based on measuring the relevant voltages and currents.

Power stage

The power stage schematic.

Shown above is the schematic for the power stage. Mains voltage enters on the top left, where it is rectified and filtered to get approximately 325 V DC. Then, four IGBTs (IGBT1H, -1L, -2H, and -2L) form an H-bridge that generates the 10-100 kHz 'modified square wave' for the transformer.

The IGBTs are driven via gate-drive transformers (GDT1 and GDT2) so that the control circuitry can be isolated from the high-voltage side. These transformers in turn are driven by high-current MOSFET drivers (IC1H, -1L, -2H, and -2L), which receive their signals from the controller.

The power stage board layout. The assembled power stage board.

Coupling transformer

The coupling transformer converts the high-voltage low-current chopped mains waveform to low voltage and high current for the work coil. Using a separate coupling transformer relaxes the requirements on the workpiece coil, so it can be adapted more easily to the workpiece being heated.

It'll be made from four stacked 100 × 60 × 15 mm ferrite cores (to provide enough core cross-sectional area for the magnetic field). The primary will consist of 60 turns of thick litz wire, and the secondary will be 2 turns of 15mm OD copper tubing, giving a winding ratio of 30:1.

Pledges

So far, the following has been pledged:

  • Gori: 50 euro
  • Flok: 10 euro
  • Walter: 50 евра
  • FooBar: €20 cash betaald
  • bertrik: €10
  • Semafoor: €20
  • Morphje: EUR 10 (and driving to the hardware store once)

Total pledges: €170

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