I. Basic Concepts of Medium-Frequency Induction Heating Frequency
A medium-frequency induction furnace is a device that uses the principle of electromagnetic induction for heating. Its operating frequency typically ranges from 150Hz to 10000Hz. The heating frequency is one of the most critical technical parameters of a medium-frequency induction furnace, directly affecting heating efficiency, heating depth, and energy distribution. The selection and adjustment of the frequency need to be determined based on the material, size, shape of the workpiece to be heated, and the heating process requirements.
The frequency adjustment of a medium-frequency induction furnace is essentially achieved by changing the operating parameters of the inverter. Modern medium-frequency induction furnaces mostly use inverter circuits composed of power semiconductor devices such as IGBTs or MOSFETs. By controlling the conduction and cutoff timing of these switching devices, the output frequency can be flexibly adjusted.
II. Technical Principles of Frequency Adjustment
1. Inverter Control Principle
The inverter of a medium-frequency induction furnace is a key component that converts DC power into medium-frequency AC power. Frequency adjustment is mainly achieved by changing the trigger pulse frequency of the inverter switching devices. The control system usually uses PWM (Pulse Width Modulation) technology, and the output frequency is changed by adjusting the carrier frequency and modulation ratio.
2. Resonant Frequency Matching
When the medium-frequency induction furnace is working, the inverter output circuit, induction coil, and load form a resonant circuit. When adjusting the frequency, the resonance point needs to be considered so that the operating frequency is close to or equal to the resonant frequency to obtain the highest energy transfer efficiency. This requires real-time detection of the voltage and current phase difference and feedback to the control system for dynamic adjustment.
3. Phase-Locked Loop Technology
Modern medium-frequency induction furnaces often use Phase-Locked Loop (PLL) technology to achieve precise frequency control and automatic tracking. When load characteristics change, causing the resonant frequency to drift, the phase-locked loop can quickly capture the new resonant point and adjust the inverter output frequency accordingly, keeping the system always operating in the optimal state.
III. Specific Methods of Frequency Adjustment
1. Manual Frequency Adjustment
(1) Adjustment via control panel: Most medium-frequency induction furnace equipment is equipped with a human-machine interface, allowing operators to directly input the target frequency value or adjust it through knobs and buttons.
(2) Potentiometer adjustment: Some traditional equipment uses analog circuit control, and the operating frequency of the oscillation circuit is adjusted by rotating the potentiometer to change the reference voltage. (3) Jumper or DIP switch settings: Some devices allow selecting preset frequency ranges via hardware jumpers or DIP switches.
2. Automatic Frequency Adjustment
(1) Adaptive frequency tracking: Advanced digital control systems can monitor load impedance changes in real time and automatically adjust the frequency to match current load conditions.
(2) Programmed frequency control: Programmable logic controllers (PLCs) or dedicated control chips can automatically switch operating frequencies according to preset process curves during different heating stages.
(3) Remote frequency adjustment: The operating frequency of the medium-frequency furnace can be set and adjusted remotely from a host computer via industrial communication networks (such as PROFIBUS, Modbus, etc.).
