Introduction to the electronic board of induction furnaces

These boards are digital and the controllers are implemented in software and can be installed on all types of furnaces with parallel, series, and series-parallel topologies. These boards are designed with the following goals: reducing electronic circuits and simplifying hardware, thereby increasing reliability, covering various needs in induction furnaces, such as using crucibles with different tonnages with one electrical panel, making the furnace easier to use, reducing the need for expertise for melting operators, allowing for the development of various sections in the future, high isolation of the board inputs and outputs, which significantly reduces damage to . the electronic section.

Example of an installed board

An example of a board installed on an AEG furnace at Tabriz Machine Foundry

An example of a digital board

Installed on the Indo-German EMA stove

Digital part of the control board

4 layers with two ARM processors and one CPLD

Specifications:

  • Digital Control System: This board has an ARM processor with floating point computing capabilities. All controllers are implemented on this processor. Also, to prevent any damage to the power circuit due to a possible processor stop, an FPGA is also used alongside it. The FPGA is responsible for receiving and sending pulses and for final processing and protection operations.
  • Separate inverter and rectifier transformer signal card: This card is connected to the control board via a flat cable. The transistors for the transformers are located on this card. This card also has current protection that protects the system in case of an increase in the transformer current. There are 2 fuses on this board, and if an LED burns out, it lights up next to them and the operator is also informed on the HMI.
  • Has RS485 port with standard MODBUS/RTU protocol for connection to local HMI or PLC
  • Possibility of parameter settings from local HMI
  • Sending power, voltage, current and frequency information to HMI
  • Sending electronic error information to HMI
  • Has service mode for testing: rectifier, rectifier pulses and inverter pulses, 10 ms test
  • Has separate power supply for the control board and the thyristor command board.
  • Has test points to measure voltages and currents input to the board.

In this board, the controllers are implemented in software. These controllers are:

1- Power control: Controls the power of the stove by volume. The maximum power value is adjustable.

2- Frequency controller: This controller is responsible for matching the output frequency with the resonance frequency.

3- TURBO controller: By increasing and decreasing the voltage with this controller, the output power can be kept at the appropriate value in different conditions. This controller operates completely automatically and causes the furnace to always work at the highest possible power. One of the most important effects of this controller is the reduction of reactive power at the furnace input.

4- Current limiting controller: If the current increases beyond the rated value, this controller comes into action and keeps the current value continuously at the rated value. The current limit is adjustable.

5- Voltage limiting controller: If the voltage increases beyond the rated value, this controller comes into action and keeps the voltage continuously at the rated value. The voltage limit is adjustable.

When the error is corrected, the food is delivered to the customer along with the plate.

Test section:

When a furnace fails, it is necessary to perform partial tests on the furnace during and after the repair to ensure the correct functioning of the repaired part. To achieve this goal, a test system has been designed. This system has the following capabilities:

  • Sending rectifier pulses: When the three-phase power voltage is interrupted, these pulses are sent to test the transformer pulses and ensure correct wiring.
  • Sending inverter pulses: Inverter pulses are sent. In this case, the pulse transformer and wiring are checked.
  • Rectifier test: With the presence of input voltage, only the rectifier is turned on and its performance is tested. In this case, the inverter is off.
  • 10ms test: For a short period of 10ms, the device is fully and automatically turned on and off. During this period, it is not possible to increase the current and voltage to high values. By recording the waveform on the oscilloscope, the system performance can be evaluated before it is turned on permanently and the problem can be solved.

Errors:

To prevent damage to the device, various errors have been designed and built into the system, including:

Output voltage error
Output current error
Input current error
Input and output current difference error
Minimum frequency error

Error number 4 significantly increases the speed of fault detection in the power circuit.

Digital inputs

This board has a number of digital inputs that are similar to those of a PLC. Temperature, pressure, and water flow sensors can be connected to it. There are 6 of these types of inputs.