Abstract: As a metal solution stirring equipment driven entirely by electromagnetic force and having no contact with metal solution, the electromagnetic mixer can improve the overall uniformity of alloy, shorten smelting time, reduce burning loss and improve product quality. This paper mainly introduces the advantages of four quadrant inverter in electromagnetic stirring equipment.
Keywords: metallurgical electromagnetic stirring
1. Preface
As the key equipment in the metal smelting process, the electromagnetic mixer has been widely used in the metallurgical industry, and has the advantages of no contact pollution, uniform solution temperature, short smelting time, the same chemical composition, reduction of oxide slag, low burning loss, high index controllability and high electrification level. Variable frequency power supply is an important part of electromagnetic mixer, and its characteristics determine the quality of metal smelting, energy-saving effect and mixing quality index. Generally speaking, the traditional power supply of the electromagnetic mixer is AC-AC or two quadrant AC-DC-AC, which has many defects, such as low power factor, large harmonic interference, infeasible power grid energy feedback, and sudden power failure, which is easy to cause explosion accidents. The four quadrant inverter can be scientifically configured to provide the electromagnetic stirring system with variable frequency power supply, thus avoiding many defects of the traditional power supply.
2. Working principle of electromagnetic mixer
Induction electromagnetic mixer is mainly composed of variable frequency power supply and inductor. According to the principle of electromagnetic induction, the high intensity magnetic field acts on the metal solution (conductor), thus making it move regularly. The variable frequency power supply changes the 50/60Hz AC power frequency to an adjustable output voltage of 0.5~5.0Hz. The variable frequency separated low-frequency power supply forms an alternating moving magnetic field when the power passes through the inductor. The moving magnetic field acts on the metal solution by penetrating the stainless steel plate at the bottom of the furnace. Under the action of the magnetic field, the metal solution generates an induced electromotive force and an induced current. At the same time, under the interaction of the magnetic field, the induced current generates an electromagnetic force, Thus, the metal solution can move regularly to achieve the purpose of solution stirring. Changing the direction and intensity of the moving magnetic field can effectively control the stirring direction and intensity of the metal liquid.
3. Technical requirements for variable frequency power supply
• Frequency conversion separation control;
• Communication between upper computer touch screen and MODBUS;
• Voltage level: AC 380V;
• Power factor ≥ 0.96, full load above 0.98;
• AC-DC-AC four quadrant frequency converter;
• Allowable three-phase output current unbalance ≥ 15%;
• Adjustable frequency 0.5Hz-5HZ, normal operating frequency 0.5Hz-1Hz;
• Frequency adjustment resolution 0.1Hz (minimum), 0.05Hz (optimal);
• Operation time can be set;
• Countdown stop setting;
• Low frequency large inductance device;
• It is necessary to consider the energy release of load inductance during emergency stop.
4. Advantages of four quadrant inverter in electromagnetic stirring equipment
The four quadrant inverter of variable frequency power supply is a high-performance inverter specially developed for high-end market. Its current rating is designed according to the high load condition, so it is suitable for the environment with high overload capacity, high reliability and continuous operation. By adopting the internationally popular modular design, the four quadrant inverter can provide rectifier unit, inverter unit and filter unit or a whole set of equipment to meet the requirements of OEM and integrated system users and customers. Its technical features are as follows:
● IGBT active part is adopted for rectification. PWM modulation can convert regenerative energy into power, and then feed it back to the grid. The power factor can reach above 0.98, so maximum energy saving can be achieved;
● The bus voltage and output voltage are continuous, controllable and stable (the impact of grid side voltage fluctuation is less), which solves the impact on metal smelting caused by large voltage fluctuation of AC-AC frequency converter or ordinary two quadrant frequency converter;
● Provide frequency conversion control, open loop vector control and closed loop vector control, support frequency conversion separation, and solve the automatic protection problem of safe shutdown when the electromagnetic mixer works normally under special load;
● Modular structure design is adopted to facilitate assembly and on-site maintenance; The wiring of each unit is top in and bottom out, meeting the public DC bus scheme;
● Optical fiber communication is adopted between units to realize photoelectric isolation between main control board and unit control, and ensure the reliability of the system under the special requirements of long-distance transmission;
● Support a variety of communication protocols, including Modbus, Profibus, CAN, Ethernet and DeviceNet, and apply to various industrial applications;
● Provide perfect frequency conversion protection function. In addition to the traditional protection functions, such as over-current protection, over-voltage protection, and over temperature protection, it also pays attention to the protection of the motor side. Through the temperature detection terminal, the operating temperature of the motor is detected in real time to provide effective over temperature protection;
● Standard STO (safety shutdown), SS1 (safety stop 1), SLS (safety speed limit) and SBC (safety braking control) protection maximize the safety and reliability of the system;
● EMC performance shall meet C3 requirements.
5. Summary
With the rapid development of economy, China pays more attention to industrial pollution and energy conservation of industrial equipment. Due to its various advantages, such as green, environmental protection, energy saving and perfect functions, the four quadrant inverter will be widely used in the electromagnetic stirring equipment of the metallurgical industry.