Abstract: This paper introduces the features and applications of the MAGNAMATBDM digital rectifier device designed and manufactured by MH Company in the UK. It uses two back-to-back fully thyristor rectifier bridges for lifting electromagnets to control the lifting and demagnetizing currents. The control part is completed by a microprocessor, which effectively solves various problems existing in traditional rectifier devices. Keywords: thyristor; electromagnet; rectification [b]1 Introduction[/b] Lifting electromagnets are widely used in machinery, metallurgy and other industries. They have the advantages of large holding force and simple operation, which greatly reduces the labor intensity of workers and reduces production costs. They are one of the main lifting tools of cranes. Electromagnets have a simple structure. When their internal windings are connected to a DC power supply, they generate electromagnetic attraction. Even the simplest half-wave rectification can make them work. Therefore, the rectifier devices used by users are varied and non-standard. Most rectifier devices lack filter circuits and demagnetizing circuits, resulting in excessive AC components in the DC power supply. The output voltage far exceeds the rated voltage range of the electromagnet, causing the electromagnet's lifespan to be shortened and the number of damaged electromagnets to increase. Electromagnets use copper or aluminum for their internal windings, with a single electromagnet costing between 60,000 and 120,000 yuan, and repair costs exceeding tens of thousands of yuan. Taking a steel plant with an annual output of 2 million tons of steel as an example, approximately 20 electromagnets fail each year, with new purchases and repairs costing over 1 million yuan. To reduce the number of failures and lower maintenance costs, it is urgent to address the various problems associated with traditional rectifier devices. 2. Traditional Rectifier Devices The characteristics of traditional rectification methods are: simple structure, non-adjustable output voltage, large AC component, and significant high-order harmonics. The selection of traditional rectifier devices is mainly based on the device's economic efficiency and ease of maintenance, often using simple three-phase or single-phase diode rectifier circuits (such as half-wave rectification, bridge rectification) and irregular waveform rectification (such as A and B phase half-wave rectification superimposed on phase C). The circuit diagram is shown in Figure 1. The rectification method employs a two-phase (A and B) half-wave rectification superimposed with a C-phase AC rectifier. Its output voltage is around 250V, with relatively soft output characteristics and voltage fluctuations within the allowable range, eliminating the need for a transformer. The circuit diagram is shown in Figure 2. [align=left] Most rectifiers lack system protection devices. When the system experiences overcurrent, short circuit, or overvoltage abnormalities, the rectifier and electromagnet are easily damaged. At the moment of power failure, the electromagnet's internal windings act as a large inductor, generating a considerable self-induced electromotive force, reaching thousands of volts. Due to the lack of a demagnetizing circuit, an arc discharge occurs. The windings generate high voltage and high current during this process, which, over time, accelerates winding aging and shortens the electromagnet's lifespan. 3 MAGNAMATBDM Digital Rectifier The MAGNAMATBDM digital rectifier, designed and manufactured by MH Company in the UK, is based on fully thyristor rectifier bridge technology and is specifically designed for DC power supply systems for electromagnets. It features advanced design, strong targeting, and comprehensive protection functions. 3.1 Working Principle The device uses two back-to-back fully thyristor rectifier bridges. One is used to supply the lifting current and the other is used to provide the demagnetizing unloading current. Both bridges are also used to feed the energy stored by the electromagnet back to the power grid. The voltage amplitude applied to the electromagnet can be adjusted by the intelligent circuit. The voltage changes proportionally and is suitable for controlling electromagnets with DC voltages from 220V to 400V. The control circuit is completed by a microprocessor. The microprocessor controls the thyristor trigger circuit according to the measured signal, the set parameters and the instructions of the I/O port. 3.2 System Advantages (1) Wide range of applications, especially suitable for cranes used in metallurgical high-temperature environments and environments above 60°C, without the need for special air cooling measures; (2) Good control accuracy, can realize constant voltage or constant current control; (3) Has four application functions, can control electromagnets for various applications; (4) No contactor is required, realizing contactless control; (5) Simple installation, no need for on-site debugging, high reliability and safety, low failure rate, easy replacement of spare parts, especially suitable for the modification of cranes. 3.3 Application Functions of the MAGNAMATBDM System The MAGNAMATBDM digital rectifier can realize four application functions depending on the user and environment: lifting/holding; lifting/forced excitation; plate lifting; and constant current. Each function is implemented by a different typical circuit. For example, in the lifting/holding function, when a lifting signal is input, a forced excitation current is output during the forced excitation time to generate strong magnetization on the electromagnet for lifting. The device can automatically input a holding voltage to the electromagnet to maintain the magnetic force. When a demagnetizing signal is input, the device outputs a demagnetizing voltage to the electromagnet during the demagnetizing time to demagnetize. The circuit diagram is shown in Figure 3. 3.4 Protection Functions of the MAGNAMATBDM System The MAGNAMATBDM digital rectifier has multiple intelligent protection functions. These mainly include: short-circuit protection for the main circuit and control circuit; phase loss protection for input voltage and phase sequence; output voltage and current protection; and device protection. [b]4 Conclusion[/b] Lifting electromagnets are widely used in modern machinery, metallurgy, mining and other industries, but the costs are high. The MAGNAMATBDM digital rectifier can reduce equipment failure rates in practice, while saving on electromagnet maintenance and purchase costs, making it a valuable tool for widespread adoption. [/align] Click to download: Digital Electromagnet Rectifier Based on Fully Thyristor Rectifier Bridge Technology Editor: Chen Dong