SU312343A1 - MACHINE-VENTILA CASCADE - Google Patents

Description

The proposed cascade relates to electric drives operating in a constant power mode used for high-speed, high-power mechanisms.

The well-known machine-valve cascade with asynchronous and synchronous electric motors, whose shafts are rigidly interconnected, and the rotor winding of the asynchronous motor is connected to the stator winding of the synchronous motor through series-connected rectifiers, and has relatively poor energy indicators.

The proposed cascade is more perfect, so. It makes it possible to increase the adjustment range and rigidity of electromechanical characteristics, increase the stability of the electric drive system, and reduce its dimensions.

This is achieved by the fact that one of the rectifiers is controlled and operates in the inverter mode, and the excitation winding of the synchronous machine is connected at one end to the output of the rectifier, and the other. - to the input of the diverter, slave, synchronous machine; at low speeds of the cascade, the stator winding of the induction motor switches from a triangle to a star; the synchronous motor is supplied with an additional winding of independent excitation, or is covered by a positive feedback on the load current.

FIG. 1 shows the scheme of the proposed cascade; in fig. 2, 3-waveforms of transients at different ways of starting the cascade; in FIG. 4-electromechanical characteristics; in fig. 5 shows a cascade with positive feedback on the load current of a synchronous motor.

Machine valve hub.d contains a synchronous motor /, the rotor winding 2 of which is turned on to input of rectifier 3 with flattening throttle 4. Starting resistance 5 and contactor 6 are connected to output terminals of rectifier 3. Consistently with rectifier 3 and driven synchronous machine by inverter 7, an excitation winding 8 of a synchronous motor with a shunt of a treading branch is included, consisting of inductance 9 and regulating resistance 10. Inverter 7 feeds an auxiliary synchronous motor 11, the shaft of which is rigidly connected to the shaft a synchronous motor. The inverter 7 valves are controlled by a control system consisting of a phase-regulating unit 12, blocking generators 13. Switching of the valves in the inverter circuit occurs in time with the cascade shaft rotating by connecting the control system with the stator winding of the synchronous motor 1L in this way. The inverter control circuit initially provides for the simultaneous unlocking of the valves through one of the anodic and cathodic groups of different phases. Thus, at one time, the impedance of the excitation winding and the stator core current of the synchronous motor, limiting the starting current, is introduced into the rotor circuit of the induction motor, at the time of the start-up of the asynchronous motor (see Fig. 2). After the shaft turns in a stator winding of a synchronous motor, an emf is induced. rotation, sync, control inverter control. The inverter automatically enters the three-phase operation mode. The cascade is started in a known manner (see Fig. 1) by switching on the contactor 6 to the input of the rectifier J of the lusk resistance 5, which short-circuits the rotor of the induction motor (see Fig. 3) while the cascade is started. In this case, the excitation voltage of the synchronous motor is preliminarily applied and a predetermined inversion angle is established. After turning on the induction motor and turning the shaft, an emf is induced in the stator winding of the synchronous motor. rotation, providing synchronization of the inverter with a rotating synchronous motor. In the regulation mode below the synchronous speed (see Fig. 1), a counter-emf is introduced into the rectified current Id circuit of the rotor of the asynchronous motor 1. the inverter 7, due to the excited synchronous motor 11. Natural switching of the current in the inverter circuit is carried out by the emf. rotation of a synchronous motor, providing the phase-ahead load current. Inverter valves alternately close the rectified voltage On. rotor induction motor 1 on the phase of the stator winding of a synchronous motor, which gives in this part of the period the greatest positive (for the anode valve group) and negative (for the cathode group) emf As a result, the synchronous motor consumes a current directed opposite to the emf and develops the motor torque. The automatic regulation of the magnetizing force of the excitation winding of the synchronous motor, necessary to compensate for the demagnetizing effect of the load current along the longitudinal axis, is achieved in series by the excitation winding 8. The electromagnetic moment developed by the cascade represents the sum of the moments developed by motors 1 and 11. This moment is proportional to the rectified current Id, which is controlled by changing the value of the emf added to the circuit, determined by the average input voltage inverter (counter-emf. inverter). The effective value of the input voltage f / E of the inverter is balanced by the rectified voltage of the rotor of the induction motor. With increasing or decreasing back-emf. the inverter corresponding change in the excitation current of the synchronous motor or the inversion angle p decreases, or the torque developed by the motor increases. In this case, the drive is slowed down to a lower value of the speed or accelerated to a larger value, at which electromechanical equilibrium occurs in the cascade. With the inverter's input voltage completely removed (or p 90 °), the cascade speed is close to the nominal speed of the induction motor, and the electromagnetic moment is developed only by this motor. As the input voltage of the inverter increases, the cascade speed decreases, and the torque developed by the synchronous motor increases, as a result of which the asynchronous motor is unloaded by the moment and power developed. In this case, the slip energy minus losses by means of an inverter and a synchronous motor returns to the cascade shaft. If the input emf. If the inverter is equal to the rectified voltage of the rotor of the asynchronous motor, then the current in the circuit of its p tor and the electromagnetic moment of the cascade will be zero. The full range of the cascade control speed is determined by three ways to control it (see Fig. 4). The first method provides an adjustment interval between the natural characteristics of the asynchronous motor and the cascade. It is obtained by converting the inverter to the rectifying mode and the minimum excitation current of the synchronous motor. The second method covers the range of regulation of the excitation current of a synchronous motor from the minimum to the maximum value at a constant maximum inversion angle or vice versa. The third method covers the interval of adjustment of the inversion angle from the maximum to the minimum value allowed at a constant maximum excitation current of a synchronous motor or vice versa. When the stator winding of a synchronous motor is switched from a triangle to a star, the cascade speed control range under other equal conditions increases by a factor of. The cascade circuit performs dynamic braking with self-excitation or with independent excitation of a synchronous motor. In this case, the asynchronous motor is disconnected from the mains, and the inverter is switched to the rectifying mode. The current in the rectifier circuit is limited by the angle of the venille of the inverter group or the excitation current of the synchronous motor. FIG. 5, the power supply of the independent excitation winding of the synchronous motor 11 comes from the source 14 controlled by the signals: the t / y driver and the positive current / load feedback carried out by the current transformer 15.

The principle of operation of the cascade of FIG. 2 in the start, speed control and deceleration mode is similar to that of FIG. one.

Subject invention

Claims (3)

1. Machine-valve cascade with asynchronous and synchronous motors, the shaft of which is rigidly interconnected, and the stator circuit of the synchronous motor is connected to the rotor circuit of the induction motor through two series-connected rectifiers, characterized in that, in order to increase the rigidity of electromechanical characteristics and one of said rectifiers is controlled and operates in the inverter mode, while the excitation winding of the synchronous machine is connected at one end to the output of the rectifier, and the other end to the inverter input. 2. Machine-valve cascade according to claim 1, characterized in that, in order to reduce the size, at low speeds, the stator winding of the induction motor switches from a triangle to a star. 3. Machine and valve cascade on PP. 1 and 2, characterized in that, in order to maintain a given rigidity of electromechanical characteristics, the synchronous motor is supplied with an additional series excitation winding. -Uk Lllll L / h Lll Lllll Lll Puz.2 I rheostat i nycK 6 off well - “J, L 02 sec  l / l / vm / l l / 1 / 1llllllllllll Natural characteristic / 5L