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Speed Control System for Dual-drive Semi-autogenous Mills

On May 9, 2015, Zhiguang Electric's intelligent HV variable frequency speed control system for dual-drive semi-autogenous mills was successfully debugged in a mining company limited to the China National Gold Group Corporation and passed the direct HV motor load test. With an altitude of 4,800 m, the Phase II metal mining field expansion project of such company is located in a county of Mozhu, Tibet. Thanks to its advanced technologies and strength, Zhiguang Electric has refreshed its record on the operation of ultra-high power frequency converters with high altitudes.
As an on-site load, each semi-autogenous mill is driven by two 5,500 kW synchronous motors simultaneously. Both motors are hard-wired by connecting to a gearbox, in which gears engage with those fixed on the mill roller, through pneumatic clutches. On one hand, although it is required to operate such two motors concurrently, a power deviation will occur between them and be accumulated if no power balance control is performed, due to machining errors or differences in the start time, acceleration or deceleration at their startup, consequently resulting in unbalanced system output power. On the other hand, the requirement of synchronous motors for accurate synchronous control is higher compared with asynchronous motors. Otherwise, the deviation of the phase angle between stator voltage and rotor bucking potential will be increasingly larger once a speed difference occurs during operation of both motors. As a result, system unbalance and out-of-phase motor failure will happen. Therefore, the requirements for the response speed and control accuracy of the power balance control are very high.
Through its two years of hard work, Guangzhou Zhiguang Electric Co., Ltd. developed the intelligent HV variable frequency speed control system for dual-drive semi-autogenous mills. Featuring a unique control algorithm (i.e. improved vector control algorithm for synchronous motors), such system can fulfill the accurate decoupling control of motor torque current and the real-time adjustment of the phase angle between stator voltage and rotor bucking potential, so as to accurately control the torque current and power. Moreover, such variable frequency speed control system can achieve the power balance between both motors without an encoder for detecting the rotor position through its own smart accurate control, which has eliminated the difficulty in the power balance control of dual-drive semi-autogenous mills during variable frequency operation.
Previously, a multinational corporation monopolized the integrated motor system of dual-drive semi-autogenous mills. During operation at the power frequency, it adopted the Q-axis excitation control technology for the power balance between both motors and thus realized such technological monopoly. Compared with the Q-axis excitation regulation and control technology for power frequency, our control technology leads to low current during variable-frequency startup, non-impact operation and mill speed control based on required processes, thus leading to significant energy conservation effects and excellent speed control performance. Besides, it significantly improves the control performance of semi-autogenous mills and reduces the demands of such mill systems for energy consumption and power capacity. The successful development of such technology has broken the technological monopoly of foreign technologies concerning such process control. It has finished an important step for promoting the applications of domestic frequency converters and motors in this field. Apparently, it has significant economic and social benefits.
  

Speed Control System for Dual-drive Semi-autogenous Mills

 

Speed Control System for Dual-drive Semi-autogenous Mills

 

 

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