JPS6117237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a hysteresis motor.

A hysteresis motor is a self-startable synchronous motor with a simple and robust structure, which has a nearly constant torque from start to synchronization, and has the ability to smoothly synchronize a load with large inertia. Figure 1 shows an example of the load characteristics of a hysteresis motor. In the diagram
Psmax is the synchronous escape output. As shown in the figure, as the load increases, the efficiency η and the power factor pf increase, and reach their maximum when synchronization is released. However, in consideration of the margin for load fluctuations, the synchronous escape output Psmax of the hysteresis motor is usually set to be considerably larger than the rated load pn. For this reason, the efficiency at rated load may be less than 70%, and the power factor may be less than 20%. This increases the ratio of power supply capacity to output of the hysteresis motor.

In order to improve these power factors, there is a method of overexciting a synchronously operated hysteresis motor for a short period of time. Conventional methods for overexcitation include methods of temporarily increasing the voltage of the power supply and methods of temporarily lowering the frequency of the power supply.

However, when a hysteresis motor is applied to a continuous process system, failure of the power supply may cause serious damage, and it is not desirable to provide the power supply with more functions than necessary.

The present invention has been made in view of two points, and an object of the present invention is to provide a hysteresis motor driving method capable of efficiently and stably operating a hysteresis motor without modifying a power supply device. There is a particular thing.

Hereinafter, the present invention will be explained with reference to an embodiment shown in FIG.

In FIG. 2, 1 is a power supply device that supplies AC input to a hysteresis motor, 2 is a switch that can be controlled to open and close, and 3 is a hysteresis motor. Of these, the switch 2 can simultaneously have a short-circuit protection function for the hysteresis motor 3 and a switching control function for monitoring the rotation speed of the hysteresis motor 3 by detecting the back electromotive voltage frequency. 4 is switch 2
This is a control circuit that controls opening and closing, and an example of the opening and closing control output is shown in Fig. 3(a). In Figure 3, the period T
An open finger is output from the short-time control circuit 4 of ΔT to the switch 2 each time.

Next, the operation of the hysteresis motor driving method of the present invention configured as described above will be explained.

FIG. 4 shows the hysteresis curve of the rotor of the hysteresis motor 3 approximated by a parallelogram. The torque T _M of the hysteresis motor 3 is given by T _M =KB ² m sinφ (1). Here, Bm is the maximum fundamental wave value of the rotor magnetic flux density, and φ is the phase angle between the rotor magnetic flux density fundamental wave and the gap magnetomotive force. Therefore, the larger the phase angle φ is for the same magnetic flux density, the larger the torque T _M becomes, but conversely the input power factor Pf decreases.

In FIG. 3, it is assumed that the current I _M1 flows through the hysteresis motor 3 before overexcitation. The hysteresis curve of the rotor at this time becomes the curve shown by the dotted line in FIG. When an open command is output from the control circuit 4 at time t ₀ , the switch 2 becomes open and the supply of AC input to the hysteresis motor 3 is stopped. At this time, the hysteresis motor 3 rotates in a free running state. Switch 2 after time △T
When the opening command is released, the switch 2 becomes conductive again, and AC input is again supplied to the hysteresis motor 3. At this time, the current I _M flowing through the hysteresis motor 3 is the sum of the steady current and the overcurrent. However, the input power factor of the hysteresis motor 3 is poor, and therefore the time constant is large, so that the overcurrent decays slowly. Therefore, a current greater than the maximum value of the steady current flows through the hysteresis motor 3. Then,
The gap magnetomotive force generated by this lash current is as shown by _H2 in FIG. The rotor magnetic flux density increases due to this gap magnetomotive force, but after the overcurrent is attenuated, the hysteresis curve becomes like the solid line in FIG. 4 due to the hysteresis characteristic. That is, the magnetic flux density of the rotor after the switch is re-closed increases from the magnetic flux density before opening. However, when the load torque is constant, Bm increases after re-input in equation (1), so sinφ, that is, φ decreases. As a result, the input power factor of the hysteresis motor 3 is improved,
Input current I _M decreases to I _M2 . It is sufficient for the rush current to flow for one cycle. Input current I _M
The change in is shown in Figure 3(b).

The opening time ΔT of the switch 2 must be short enough to prevent the hysteresis motor 3 from slipping.
This is because, even if overexcited by the lash current, when the hysteresis motor 3 is in a slipping state, the magnetomotive force applied to each point of the rotor changes to draw a hysteresis loop, and the magnetic flux level of the rotor immediately changes. This is because the state returns to the state before overexcitation.

When a large load change occurs, the hysteresis motor 3 transiently enters a slipping state, and the overexcitation state is also released. Therefore, even if it is once excited to an overexcited state, it may be canceled due to load fluctuations. Therefore, as shown in FIG. 3(a), the switch 2 is repeatedly opened for a short time every cycle T.
By doing this, even if the overexcitation is canceled due to load fluctuation or other disturbance, the overexcitation is resumed at the next short-time release, so stable overexcitation operation is possible.

Incidentally, when operating a large number of hysteresis motors, it is more advantageous in terms of cost to provide switches for each group as shown in FIG. Furthermore, in order to reduce load fluctuations on the power supply device 1, it is better to open each switch for a short time one after another in a time-sharing manner.

Further, an embodiment of the present invention is shown in FIG. In FIG. 6, the same parts as in FIG. 2 are given the same reference numerals, and their explanations will be omitted. 5 is a current transformer that detects the input current of the hysteresis motor 3; 6 is a comparator that compares the input current value with the set value I _R ; and 7 is a comparator that outputs the result as a logic signal; A pulse generator that generates a pulse after a certain period of time after the input current transient has sufficiently decayed.
8 is an inverting circuit, and 9 and 10 are AND circuits.

Next, the operation of another embodiment of the present invention constructed as described above will be explained.

When starting the hysteresis motor 3 for the first time, the hysteresis motor 3 is naturally in a slipping state, so that no overexcitation state occurs. Therefore, after the open command is output from the control circuit 4 and the switch 2 is opened for a short time, the steady input current of the hysteresis motor 3 remains unchanged from before the switch 2 is opened and is equal to or higher than the set value. Therefore, the output of the comparator 6 is at a high level, and when a pulse is generated from the pulse generator 7, the AND circuit 9 outputs a voltage strengthening command S _R to the power supply device 1. As a result, the output voltage of the power supply device 1 becomes a strong voltage _VH , and the hysteresis motor 3 is coupled with sufficient power.

When the hysteresis motor 3 enters the synchronized state, an overexcitation phenomenon occurs, so that the steady input current of the hysteresis motor 3 becomes less than or equal to the set value I _R . Therefore,
Since the output of the comparator 6 is at a low level, when a pulse is generated from the pulse generator 7, a voltage weakening command S _L is output from the AND circuit 10 to the power supply device 1.
As a result, the output voltage of the power supply device 1 becomes a voltage V _L equal to or lower than the rated voltage of the hysteresis motor 3, and the input to the hysteresis motor 3 is reduced, resulting in efficient operation.

As explained above, in the present invention, a switch is provided between the power supply device and the hysteresis motor, and the switch is periodically opened for a short time and then turned on again, so that the power supply device has an extra function. A hysteresis motor can be easily and stably overexcited without overexcitation. In addition, the switch can simultaneously function as a cutoff function in the event of a short circuit in the hysteresis motor and as a switch for monitoring the rotational speed of the hysteresis motor by detecting the back electromotive voltage frequency. The present invention becomes increasingly advantageous when evaluating the motor drive system as a whole.

[Brief explanation of the drawing]

FIG. 1 is a load characteristic diagram of a hysteresis motor, FIG. 2 is a configuration diagram showing an embodiment of a hysteresis motor driving method according to the present invention, and FIGS. 3 and 4 are operational characteristic diagrams of the motor shown in FIG. FIGS. 5 and 6 are configuration diagrams showing other different embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Power supply device, 2... Line breaker, 3... Hysteresis electric motor, 4... Control circuit, 5... Current transformer, 6... Comparator.

Claims (1)

[Scope of Claims] 1. A method for driving a hysteresis motor, characterized in that a switch provided between a hysteresis motor and a power supply device for driving the hysteresis motor is opened for a short period of time at regular intervals and then turned on again. 2. The switch provided between the hysteresis motor and the power supply device that drives the hysteresis motor is opened for a short period of time and turned on again, and the transient amount of electricity input to the hysteresis motor after the switch is turned on again. If the amount of electricity after sufficient time for the phenomenon to decay is equal to or greater than the set value, the output voltage of the power supply is increased, and if the amount of electricity is less than the set value, the output voltage of the power supply is increased. A hysteresis motor driving method characterized by lowering the output voltage.