Keywords: Supersynchronous cascade speed control technology, hoist application
Currently, most PIE control systems for AC hoists in China are based on modifications of TKD systems, and the speed regulation method still uses traditional series resistance speed regulation, which wastes energy and has low system efficiency. Its simple energy-consuming braking cannot suppress the high voltage generated by rapid braking, limiting the improvement of braking performance. General-purpose frequency converters cannot be directly applied to the speed regulation of mine hoists with rapid start-up, braking, and frequent forward and reverse rotation. To address the energy generated by the regenerative braking of motors, foreign countries have developed AC-DC-AC frequency converters, but these are expensive and have high requirements for the power grid, making them unsuitable for the realities of my country's energy companies. The application of supersynchronous cascade speed regulation technology combined with modern advanced control technology to the speed regulation of mine hoists is still rare in China. The Quanzhou Coal Mine's main shaft winch has had a supersynchronous cascade speed regulation device installed and commissioned since 2002, and its operation is currently performing well.
1 System Principles
1.1 Overview
Supersynchronous cascade speed control technology feeds electrical energy separately into the stator and rotor windings of an asynchronous motor. The stator winding is powered by a fixed-frequency industrial power source, while the frequency, voltage amplitude, and phase of the rotor winding power supply are adjusted separately using a transistor-controlled rectifier circuit, thereby regulating the torque, speed, and reactive power on the stator side of the asynchronous motor. This method prevents the motor from operating in the subsynchronous speed range but allows it to operate in the supersynchronous speed range, hence the name supersynchronous cascade speed control. Mine hoists use constant torque speed control. Based on their operating conditions and the torque loss of cascade speed control, the motor does not need to operate in the supersynchronous speed range. The application of supersynchronous cascade speed control in mine hoists eliminates the traditional eight-stage resistor and dynamic braking device and integrates the various protections of the supersynchronous cascade speed control cabinet with the original system to ensure hoisting safety.
1.2 System Principle
Figure 1 shows the schematic diagram of supersynchronous cascade adjustment applied to a mine hoist. In the figure, M_ is the main motor of the hoist, M1 is the three-winding inverter power supply transformer, Ps is the speed measuring device, ICFB is the trigger board of the rotor-side controllable bridge I, 2CFB and 3CFB are the trigger boards of controllable bridge II and controllable bridge III respectively, Z-UNIT is the serial adjustment main controller, XHZH is the internal signal processing unit, and WBSR is the input and output circuit of the external control.
For details, please click: Application of Supersynchronous Cascade Speed Regulation Technology in Mine Hoists
