Medium Frequency Induction Power Supply

Induction Power Supply Unit for Induction Heating and Melting Applications

Medium frequency induction furnaces use eddy current in the metal that helps heat the metal. Like any other appliance, the induction furnace core is the power supply unit that works and ensures heat generation for further processes. This article will discuss the medium frequency induction power supply instead of high and how it is achieved. For that, we will talk about its working and the components that are involved in working.

What is Medium Frequency Induction Furnace Power Supply?

As the name suggests, medium frequency induction power supply gives medium frequency as an output. The power we receive from the outlets typically operates at 50Hz-60Hz (Depending on the region).

However, running an induction furnace requires a much higher frequency. Due to this requirement, induction furnace power supplies are classified into three categories: low frequency, medium frequency, and high frequency.

Usually, medium-frequency induction power supply frequencies range from 1KHz to 10KHz.

Working of Medium Frequency Induction Power Supply

The core function of induction heating is non-contact heating for conductive materials. In this process, a high frequency drives an alternative current from the coil. But for the medium frequency induction power supply, there is a slight change in the phenomena of the working because it needs a filter to control the input power to make it controlled.

“There is a 3-phase input supply. First, that goes inside the power supply and enters a controlled rectifier that converts the current. Then, the current passes through the filter of LC that adjusts the frequency of the induction power supply. After this, an inverter inside the power supply is a voltage source inverter that again converts the current to its original conditions. It is then passed through the current limiting reactor that adjusts the current according to the operator’s requirements. And lastly, it goes to the furnace coil”.

In general, the converter and inverter are the main components and other than their parts do their job to keep the process healthy and quick.

Schematic diagram for Induction Power Supply Unit
Schematic diagram for Induction Power Supply Unit

1. Working of Rectifier

Overall, the main purpose of the rectifier is to convert the input power supply, that is, AC power, into the DC that will further go into the power supply. The 3-phase input supply is received in a full wave in a medium-frequency induction power supply.

It supplies that DC power to the inverter of the power supply because a DC choke inside it will only receive DC power.

When your power supply rectifier is operating, it remains fired at a maximum angle that helps the DC supply to remain at full power on the panel.

What happens when isolators and main breakers get closed?

When closed, the DC voltage goes to the valve ( a study DC: to ensure the interlocks are healthy). But in case of any failure, the gradual rising happens through which the rectifier inverter is made ON. And it is kept ON until any other interlocks fail,

2. LC Filter

The LC filter is an inductor and capacitor that allows AC and DC to pass through. The capacitor allows AC power, and the inductor allows DC power. So, what makes the LC filter great because it effectively filters. It reduces the high-frequency range to medium.

The DC choke filter rectifies the supply further for smooth supply. It has a few advantages:

  • It has a low ripple
  • No Load regulation on the transformer or rectifier
  • Voltage regulation.

3. Working of Inverter

After passing through the LC filter: the current passed to the inverter changes from DC to AC again, which is the process of inversion.

Press the ON button, enabling the oscillator to deliver the current to the inverter. After inverting it again, it delivers the AC to the coil. But at this time, various signals appear in the control section.

This process will keep switching the frequency until the operator-required power is reached.

4. Coil/Inductors

Again they are the core for the whole unit and form a winding frequency transformer, both primary and secondary (the 3-phase bridge).

The primary coil is the coil that gets the power externally, while the secondary transfers energy to create an electromagnetic field.


For any medium-frequency induction power supply, the working principle is the same as others. Still, the only difference occurs in the power circuit with an LC filter to keep the frequency at a minimum and not change it to a high frequency after the rectifier rectifies it.

The LC filter adjusts the frequency range according to your requirements