# The Design of a System for the Induction Hardening of Steels Using Simulation Parameters
## 2 Materials and Methods
### Realization of the Prototype System for Induction Hardening  
A circuit diagram of the system for the induction hardening of steel with the following characteristics is shown in Figure 3:  
* Power supply: 3 \(\times\) 400 V, 50 Hz;
* Nominal power: 15 kW;
* The inductance of the inductor coil: 32-50 \(\upmu\)H;
* Maximum energy efficiency: 95%;
* Output frequency: 10-25 kHz.  
The output frequency has varied in the range of 10-25 kHz to adjust the resonant frequency for different inductors and penetration depths.  
The three-phase mains voltage is supplied to the diode rectifier via the soft start circuit. From the rectifier, through the DC link (bus with voltage filtering capacitors), DC power is supplied to the input of the inverter.  
The inverter, depending on the parameters of the resonant circuit and the set operating frequency, with the help of the control circuit and switching elements, provides an alternating high-frequency voltage at its output. An inductor is connected to the output of the inverter, inside which there is a cylindrical steel batch, which is the subject of heat treatment (hardening). The LEM current sensor monitors the inductor current, displays it on the display and defines the overload limit.  
Due to the highly pronounced skin effect, the inductor is made of a hollow copper conductor. The losses in copper are relatively high due to the small effective cross-section through which the current flows. The inductor is cooled with water flow, and the water is cooled with airflow using a fan. Additionally, there is a fan that cools the converter components. The entire power supply system is placed in an electrical cabinet together with automatic fuses, switches, a soft start device, cooling units and signaling (Figure 4).  
Figure 4: The layout of the electrical cabinet.  
Figure 3: Electrical diagram of the induction hardening system.  
The classic rectifier circuit (transformer TR1, diodes D1 to D4 and filter electrolytic capacitors C1 and C2) provides DC voltages of \(\pm\)22V for supplying stabilized power supplies of +18V based on IC 7818, as well as \(\pm\)15V based on IC 7815 and 7915, with additional filtration (capacitors C6 to C21).  
The PWM control signal generator is based on IC SG3524 (U1) [38] with accompanying passive components. The SG3524 is a pulse width modulation (PWM) set frequency control circuit. The frequency is adjusted by an external RC branch, formed of R6, R14 and C11. The circuit also contains a current-limiting comparator and output pulse suppression circuitry. The output signals from SG3524 are fed to the IGBT driver input pins \"HIN\" and \"LIN\" of the IR2213 IC (U2) for the upper (high) and lower (low) IGBT control.  
The IGBT drivers are integrated into IC IR2213 [39]. The IR2213 is a high-voltage, high-speed driver designed for IGBT and MOSFET transistors used in power electronics. It contains two independently referenced output channels (high-side and low-side). It is suitable for applications at high frequencies and voltages up to 1200 V.  
The circuit also contains a current-limiting comparator and output pulse suppression circuitry, consisting of transistors T1 and T2 and accompanying passive components. The output conductor to the inductor is covered by a Hall effect-based current sensor (LEM), which provides a voltage output proportional to the output current. The signal from the current sensor is wired via a terminal block connector labeled as T8B, thus providing the control signal for the transistor circuit and the output current display (DISPLAY). In the case of overcurrent or the need for a manual reset, the transistor circuit stops the pulse generation by providing the signal to the SD (shutdown) pin of SG3524. The output current display is always active and shows the output current value in real time.