[ Abstract ] This paper introduces the hardware structure, control principle, and system performance of the Hitachi IGBT vector inverter system used in the 1800 continuous annealing unit. The main functions, advantages, and disadvantages of Hitachi Drives are also discussed. [ Keywords ] Inverter; PWM; Vector frequency conversion; Carrier; Control 1 Introduction The 1800 continuous annealing unit is a world-class unit designed and supplied with main equipment by Nippon Steel (NSC). It is modeled after NSC Kimitsu No. 2 C. A. P. L., with a maximum strip width of 1850 mm and a thickness of 0.45–2.0 mm. The main products are aluminum killed steel, IF steel (CQ, DQ, DDQ, EDDQ, SEDDQ), and 600k grade high-strength steel, with a designed annual output of 96.46 million tons. Its electrical drive uses a 13-inch Hitachi IGBT vector inverter system, a high-performance, multi-drive system developed based on vector control principles. It mainly consists of rectifier and inverter devices based on IGBT elements, and the control principle is primarily PWM vector frequency conversion control. Hitachi inverters can be divided into three categories: small-capacity IGBT vector inverter unit type, small-capacity IGBT vector inverter (HIVECTOL-VSI-S), and medium-capacity IGBT vector inverter (HIVECTOL-VSI-M). All inverter systems utilize a laptop computer as a maintenance tool (M.TOOL) for system maintenance. This allows for timely display of data charts and waveforms in case of faults, thus shortening troubleshooting time. The 1800 continuous-run unit employs different inverter systems based on the capacity of each motor, with its main drive using the medium-capacity drive of this system. The control principle, hardware configuration, and system functions of the Hitachi medium-capacity drive system will be introduced below. 2. Control Principle of the Drive System From a control perspective, Hitachi's small-capacity inverters and medium-capacity inline multi-stage inverters are both voltage-type PWM vector inverters. Their working principle is essentially to use vector control to convert the input DC voltage into an AC voltage with a continuously variable frequency within the motor's rated frequency range, and then output this AC voltage to the AC motor, thereby achieving continuous adjustment of the motor speed. The following is a brief introduction to the principles of PWM and vector control. For more details, please click: Application of Hitachi Inverters in Baosteel's 1800 Cold Rolling Continuous Annealing Unit