DESIGN OF REVERSIBLE THYRISTOR FEED DRIVE WITH PROPORTIONAL-INTEGRAL CONTROLLERS

This paper presents a detailed analysis of a reversible thyristor feed drive for industrial metalworking systems, oriented for application in machine tools with position or contour numerical control, as well as in copying and milling machines. The drive under consideration is based on a three-phase zero-reversing scheme, providing a wide dynamic speed control range of the executive motor speed not less than 10000 revolutions, which allows effectively adapting to changes in technological parameters and various production modes. The application of proportional-integral speed and current regulators in the control loop contributes to the accuracy, stability and speed of the system under various mechanical loads and transient modes. The paper offers a comprehensive consideration of structural features, principles of operation and performance characteristics of reversible thyristor feed drive with PI controllers. The obtained results allow to optimize the drive operation in conditions of high precision machining, to expand the functional capabilities of the machine tool equipment, to reduce the influence of external disturbances and to increase the reliability of the industrial system as a whole. The basis of the hardware configuration of the drive consists of thyristor block (BT), control unit (CU), stabilized power supply of control circuits, as well as synchronization transformer, interacting by means of functional blocks: regulator block (RB), phase shifting device (PSD), logic block (BL), stabilized power supply block (SPB) and correction block (BC). The described functional structure simplifies the procedure of initial setting of the drive, tightening the interaction of the system elements and reducing the risk of uneven operation modes. It is possible to use both conventional electric motors with normal inertia-torque ratio and motors with increased torque overload capacity or reduced inertia. An important feature of the proposed solution is a built-in system of protection of power keys against short circuits by using high-speed maximum protection automatics (MPA), which contributes to increased reliability of operation and reduces the risk of failure of expensive elements. Additional stability of thyristor switching process is achieved by using transistor electronic keys, whose operation is synchronized with the supply network due to a special transformer winding, providing fast and accurate transition between positive and negative half-periods.