SU756581A1 - Synchronous motor control method - Google Patents

Description

The invention relates to a synchronous electric drive, namely to synchronization during asynchronous start-up and resynchronization of synchronous motors, 5 especially in difficult starting conditions.

The known synchronization method of synchronous motors during asynchronous start-up, according to which the motor excitation winding closes to the discharge resistance at the time of start-up, and the excitation supply (activator activation) and discharge resistance disconnection is performed as a function of the time delay from the moment of stator winding to the voltage source [Ϊ]. This method is not suitable for engines with severe starting conditions, so which allows to fully use the syn- chronizing ability of the engine due to the excitation supply at an uncertain rotor speed and an arbitrary rotor position relative to the stator field, which leads to a large 25 shock currents and swinging moments.

The closest to the invention to the technical essence is the method of controlling a synchronous motor of 30

2

when the rotor reaches the specified slip frequency at the time of the optimum rotor position relative to the stator field, at which the slip frequency is measured by the current half-period duration in the starting resistor connected in each slip half-period to the field winding at the value induced in it EMF corresponding to a certain level [2].

This method is not sufficiently reliable due to the presence in the current of the starting resistor of higher harmonics caused by the non-adjustable voltage level of the starting of the starting resistor, which leads to inaccurate measurement of the rotor slip, disruption of the rotor positioning schemes relative to the stator field and, as a result, the excitation is not in the specified optimal moment, the emergence of shock currents and swinging moments.

The purpose of the invention is to improve the reliability of synchronization and resynchronization of the engine.

756581

This is achieved by the fact that according to the proposed method, the voltage level at which the resistor is connected to the excitation winding is changed depending on the value of the current of the pathogen so that when the current of the pathogen is lower than the specified one, the specified voltage level is reduced to the minimum close to zero.

. FIG. 1 shows a diagram of the device for implementing the proposed synchronization method; Fig 2 shows diagrams of induced voltage II £, EMF of the excitation winding and current ΐ £ in the starting resistor at the subsynchronous rotor speed of the proposed method.

The device contains a semiconductor exciter 1, made, for example, on thyristors, controlled by the excitation control unit 2. The input of the control unit is connected to the starting resistor 3, which is connected through a proximity switch 4 with an adjustable switching voltage level parallel to the field winding

5 of a synchronous motor (not shown in the figures) and the exciter 1. The 6 current comparison unit of the exciter 1 has two inputs, one of which includes the output of the current sensor 7 of the exciter 1,

and the other receives a given signal, which can have a zero value. The output of the unit 6 comparison included on the input of the switch 4 with an adjustable voltage level of inclusion.

The device works as follows.

In the prestart state, the current of the exciter 1 is absent, the deviation of the current of the exciter 1, measured by the unit

6 comparison, is equal to zero, or has a negative value, therefore, the voltage level of the on switch 4 is equal to the minimum (zero) value.

When the engine is started, the induced current of the excitation frequency of the slip frequency is closed through the switch 4 and the starting resistor 3 each half-period of the slip frequency. Since the switch-on voltage of the switch 4 is minimal, this is equivalent to a deaf connection of the starting resistor 3 to the excitation winding 5 and the flow of the almost sinusoidal slip frequency current in the starting resistor 3. The signal from the starting resistor 3 is fed to the input of the excitation control unit 2, which measures the slip frequency and position rotor relative to the stator field. At a slip frequency above a predetermined setpoint, the excitation control unit 2 outputs a signal to the input of the exciter 1, prohibiting its activation, i.e. for the period of engine acceleration, the pathogen 1 is locked, the current of the pathogen 1 is equal. zero and the voltage level of the on switch 4 remains minimal. When the rotor reaches a predetermined speed and, consequently, a predetermined slip frequency and optimum rotor position, the excitation control unit 2 2 turns on the exciter 1. This causes an excitation current and a signal at the output of the current sensor 7, When the excitation current exceeds the specified value at the output of block 6 comparison, a signal appears that changes the voltage level of the on switch 4 to the maximum possible, which exceeds the maximum value of the emf of the power supply of the pathogen, which leads to the disconnection of the starting resis ora 3 and the retraction of the engine in synchronism _(ekl point 1 in FIG. 2). '

As seen in FIG. 2, the measured signal r _and is equal to the real one at zero level of the turn-on voltage of the starting resistor. After the excitation is applied, the switching on level of the starting resistor changes to the maximum possible, exceeding the emf of the pathogen.

When the motor falls out of synchronism, the resulting voltage from the excitation winding exceeds the emf supply voltage of the pathogen, which leads to a reduction in the current of the pathogen to zero and the appearance of a signal at the output of the comparator unit 6, which changes the voltage level of the on switch 4 to the lowest possible (close to zero). Starting resistor 3 is almost tightly connected to the excitation winding, at the output of node 2 a signal appears that removes control pulses from the thyristors of the pathogen 1. In the future, the device's operation mode is similar to the start mode.

Using the proposed method allows to improve the reliability of synchronization due to more accurate measurement, slip frequency and rotor position, achieved by changing the voltage level of the starting resistor switch on depending on the value of the current of the pathogen. ·

Claims (1)

Claim The method of controlling a synchronous motor by supplying an excitation current to the excitation winding when the rotor reaches a predetermined slip frequency at the time of the optimum rotor position relative to the stator field, at which the slip frequency is measured by the current half-period duration in the starting resistor connected in each half-frequency of the slip frequency to the excitation winding at the value of the EMF induced in it, corresponding to a certain level, differs from the fact that, in order to increase the reliability of synchronization 5 756581 6 The voltage and resynchronization, the voltage level at which the resistor is connected to the excitation winding, changes depending on the value of the exciter current so that when the exciter current is less than the specified one, the specified voltage level is reduced to the minimum close to zero.