JPH04325894A - Controller of synchronous motor - Google Patents

Abstract

PURPOSE:To miniaturize it without enlarging the capacity of a power converter more than necessary by providing a means which controls the phase of an armature current so that it compensates the change of voltage by the reaction of the armature, monitoring the voltage of a synchronous motor. CONSTITUTION:When a current command 1m is given, an armature current of the magnitude in accordance with the current command Im flows as a sine wave current synchronized with the rotational angle thetav of the rotor of a synchronous motor, and the rotor generates specified torque and rotates. When motor torque and load torque balance and it gets in the condition of rotating at constant speed, the inner induction voltage E0 of the armature is established, and the terminals voltage V1 in accord with the reactance voltage Vx by the armature current Ia is established. A compensating signal theta which is output from a voltage compensating part 1 according to the deviation between this detection voltage V1 and voltage command V1, is added to the rotational angle thetav, and the phase of the armature current Ia is controlled so that the voltage deviation may be zero, and the reactive current changes. Hereby, it gets off without elevating the voltage of a power converter more than necessary.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a synchronous motor that uses a permanent magnet as a rotating field to drive a synchronous motor at variable speed.

0002

2. Description of the Related Art The field of a rotating field type synchronous motor includes an electromagnet system using a field winding and a permanent magnet system that does not use a field winding. With the electromagnet method, power loss due to the field winding causes a drop in efficiency, and Joule heat is generated from the field winding, increasing the temperature, causing thermal expansion of the rotor, disrupting the rotational balance, and causing abnormal vibrations. There is a problem. On the other hand, the permanent magnet system has the great advantage of not only improving efficiency as there is no power loss, but also eliminating the generation of heat by the field winding and eliminating rotational imbalance caused by thermal expansion.

Conventional permanent magnets have a property that they do not return to their original magnetic flux density when a large demagnetizing field is applied to them, so their application to large-capacity synchronous machines has been avoided. However, in recent years, the manufacturing technology of permanent magnets has progressed, and permanent magnets containing rare earth elements such as samarium, neodymium, and cobalt as main components have reached the stage of practical use.

Since the relative magnetic permeability of rare earth permanent magnets is approximately 1, which is close to the permeability of air, they have stable characteristics that are almost unaffected by external magnetic flux, and there is a trend toward applying them to large-capacity machines. On the other hand, a characteristic of a synchronous motor is armature reaction, and the magnetic flux caused by the armature current acts to increase or decrease the magnetic flux of the field poles depending on the power factor.

Furthermore, a power converter using a thyristor is generally used as a control power source for driving a large-capacity synchronous motor at variable speed, and in this case, it is usually operated at a leading power factor due to the conditions of the commutation mechanism. In the case of a leading power factor, the armature reaction acts in a direction that reduces the magnetic flux of the field.

Therefore, when the load increases and the armature current Ia increases, the air gap magnetic flux decreases and the terminal voltage V1 drops as shown in FIG. 4(A). Since this corresponds to an impedance drop due to current, a constant called synchronous reactance has been defined and is used to analyze the characteristics of synchronous motors. In an electromagnetic synchronous motor, this armature reaction can be compensated for by increasing the field flux by increasing the excitation current flowing through the field winding. However, since this is not possible with a motor using permanent magnets, as the current increases, the terminal voltage V1 inevitably decreases as shown in FIG. 4(A). Therefore, since the terminal voltage Vn at the rated output is the voltage Vn at the rated current In in FIG.
and the ability to output the rated current In. Therefore, the capacity of the power converter is required to be V0/Vn times the output required from the motor rating (this is greater than 1 due to armature reaction), resulting in a large device.

A well-known vector diagram of a synchronous motor in a leading power factor operating state is shown in FIG. 4(B). This figure shows that the terminal voltage V1 decreases due to the synchronous reactance drop voltage Vx. Note that Ф0 is the magnetic flux of the field pole, and Фa is the magnetic flux due to the armature current Ia. It can be seen that the air gap magnetic flux, that is, the effective magnetic flux Φ is the vector sum of Ф0 and Фa, and is decreasing. The angle φ between V1 and Ia is the power factor angle, and the angle δ between the internal induced voltage E0 and V1 is the internal phase difference angle.

Furthermore, in order to make the air gap magnetic flux correspond to the rated output in a state demagnetized by the armature reaction, it is necessary to increase the field flux Τ0 caused by the permanent magnet in advance. However, in the case of permanent magnets, the thickness of the magnet is increased, which increases the weight and dimensions, making it expensive.

[0009]

As mentioned above, there is a problem in that the capacity of a power converter for driving a synchronous motor using a permanent magnet as a rotating field becomes larger than necessary, making it expensive.

[0010] In order to solve the above-mentioned problems, an object of the present invention is to perform a new compensation for armature reaction, and to control a synchronous motor in a small and economical manner without increasing the capacity of the power converter more than necessary. The goal is to provide equipment. [Structure of the invention]

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an apparatus including an inverter for controlling an armature current of a synchronous motor using a permanent magnet as a rotating field. Means is provided for monitoring the voltage at and controlling the phase of the armature current to compensate for changes in the voltage due to armature reaction.

0012

[Operation] When the armature current changes in response to a change in load torque, the reactance voltage due to armature reaction changes, and the voltage of the synchronous motor changes. At this time, the above means controls the phase of the armature current according to the voltage change to suppress the voltage change due to armature reaction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the main structure of a control device for a synchronous motor according to the present invention. In Fig. 1, an inverter 1 is a voltage source inverter that converts a DC voltage Vd smoothed by a capacitor 1A into a three-phase AC voltage V1 to drive a permanent magnet type synchronous motor 2, and is used for IGBTs, GTOs, etc. Consists of self-extinguishing switching elements. The current control unit 5 uses a current reference Ia
* and the motor current Ia detected by the current detector 4, and the inverter 1 is controlled so that the deviation value becomes zero.

The position detector 3 is connected to the rotating shaft of the synchronous motor 2 and detects the rotation angle (ie, the position of the field pole) θr. The differentiator 6 time-differentiates the angle signal θa (t) and outputs the angular velocity signal ωa, and the function generator 7 generates a unit sine wave of sin ωa t according to ωa. The multiplier 8 multiplies the separately given current command Im by the unit sine wave sin ωat to obtain Im sin ωat, which is used as the current reference Ia*.

Note that three sets each of the current detector 4, current controller 5, function generator 7, and multiplier 8 are provided, and each function generator generates a unit sine wave with a phase difference of 120° to generate three-phase currents. control.

The voltage compensation control section 10 is composed of a PID controller and the like, and receives a separately given voltage command V1* and a voltage detector 9.
The terminal voltage V1 of the motor 2 detected at is compared, and a compensation signal θ is outputted according to the deviation value, which is added to θr by an adder 11 to obtain a compensated angle signal θa (t).

In the embodiment with the above configuration, the current command Im
When is given, an armature current Ia having a magnitude corresponding to Im flows as a sinusoidal current synchronized with the rotation angle θr of the rotor of the synchronous motor 2, and the rotor rotates while generating a predetermined torque. When the motor torque and load torque are balanced and the armature rotates at a constant speed, the internal induced voltage of the armature E
0 is established, and a terminal voltage V1 corresponding to the reactance voltage Vx due to the armature current Ia is established. The compensation signal θ output from the voltage compensator 10 according to the deviation value between the detected voltage V1 and the voltage command V1* is added to the rotation angle θr, and the armature current Ia is adjusted such that the voltage deviation value becomes zero.
The phase of is controlled and the reactive current changes.

In this case, the value of the voltage command V1* is the terminal voltage at no load (that is, the internal induced voltage E0)
, the compensation signal θ is set equal to the armature current I
The delay phase φ of a with respect to V1 is 1/ of the internal phase difference angle δ.
Compensation control is performed to maintain the value of 2. This state is shown in the vector diagram of FIG. 3(B). The load changes and the current Ia
When the magnitude of Vx changes, the magnitude of reactance voltage Vx changes, and the magnitude of terminal voltage V1 changes. When a deviation occurs between V1 and V1* due to this change, the compensation signal θ is controlled in a direction that reduces the deviation, and the current Ia
The phase of is controlled. As a result, the phase of the current Ia lags the terminal voltage V1 by 1/2 of the internal phase difference angle δ.

Ia when compensation control is performed in this way
-V1 characteristics are shown as characteristics c1 in FIG. 3(A). In this case, voltage command V1* is set to Vn. Note that the characteristic c2 shown in the figure shows the characteristic of the synchronous motor when voltage compensation control is not performed and the phase of the armature current Ia is simply fixed to a constant delayed phase. A second embodiment according to the invention is shown in FIG.

In this embodiment, the inverter 1 is a current source inverter that converts a DC current Id smoothed by a reactor 1B into a three-phase AC current. Further, in place of the position detector 3, a phase detector 12 is provided to detect the phase θ1 of the terminal voltage V1. In this case, the phase θ1 of V1 fluctuates due to the influence of the reactance voltage Vx, but the compensation signal θ compensates for the fluctuation, so the same effect can be obtained. Note that the phase detector 12 can also be configured to compensate for phase fluctuations due to reactance voltage.

[0021]

[Effects of the Invention] According to the present invention, when a synchronous motor using a permanent magnet as a rotating field is driven at variable speed by a power converter,
This prevents a drop in terminal voltage due to armature reaction (demagnetization effect) and prevents the voltage of the power converter from becoming higher than necessary.
It is possible to provide a control device for a synchronous motor that can have a capacity commensurate with the motor rating and has improved economic efficiency.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment according to the present invention.

FIG. 2 is a configuration diagram of a second embodiment according to the present invention.

FIG. 3 is a characteristic diagram and a vector diagram for explaining the operation of the above embodiment.

FIG. 4 is a characteristic diagram and a vector diagram for explaining problems with a conventional device.

[Explanation of symbols]

Claims (1)

[Claims] Claim 1: In a device equipped with an inverter that controls the armature current of a synchronous motor using a permanent magnet in a rotating field, the voltage of the synchronous motor is monitored and changes in the voltage due to armature reaction are provided. 1. A control device for a synchronous motor, comprising means for controlling the phase of an armature current so as to compensate for.