JPH04265684A - Operating method and device for synchronous motor employing cycloconverter - Google Patents

Abstract

PURPOSE:To suppress voltage drop of power supply by reducing reactive power when the operating frequency of a synchronous motor 1 is lower than 30Hz whereas lowering the terminal voltage when the operating frequency is higher than 30Hz thereby suppressing maximum reactive power. CONSTITUTION:When a synchronous motor 1 is operated by controlling a cycloconverter 2 through neutral point AC bias system, the cycloconverter 2 is controlled through the neutral point AC bias system only when the output frequency of the cycloconverter 2 is equal to the operating frequency of the synchronous motor 1 operating at a speed lower than a predetermined level. When the output frequency of the cycloconverter 2 reaches an operating frequency of the synchronous motor 1 operating at a speed higher than a predetermined level, field of the synchronous motor 1 is weakened and the terminal voltage is lowered.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for operating a synchronous motor using a cycloconverter, which can improve the power factor of a power source.

0002

[Prior Art] For example, a 36-arm type cycloconverter composed of a power commutating thyristor converter has characteristics such as high conversion efficiency, sine wave output, and high voltage output. Variable speed control of induction motors and synchronous motors is used to operate large-capacity equipment such as main rolling machines.

However, since this cycloconverter obtains a sine wave by controlling the control delay angle of the thyristor of the thyristor converter, it has the disadvantage that the power factor of the power source is low.

[0004] Conventionally, therefore, various methods have been devised to improve the decrease in the power factor of the power supply accompanying the control of the cycloconverter, one of which is a phase voltage trapezoidal wave control method. This phase voltage trapezoidal wave control method uses the phase output voltage of the cycloconverter as a trapezoidal wave to lower the maximum voltage and lower the secondary voltage of the power transformer. (at the time of voltage output) is increased, and the timing of large reductions is reduced. Therefore, according to such a control method, it is possible to reduce the reactive power generated due to the control delay of the thyristor of the thyristor converter and improve the power source power factor without giving special consideration to the main circuit.

[0005] Another method for improving the drop in the power factor of the power supply is a phase voltage trapezoidal wave control method in which the phase voltage is approximated to a trapezoidal wave by superimposing a voltage with a certain amplitude at a frequency three times the output frequency. There is a neutral point AC bias method that achieves the same effect. This method is widely used because the motor line voltage becomes a sine wave and no torque ripple occurs.

In particular, when driving a synchronous motor using trapezoidal wave control or neutral point AC bias method, the motor power factor can be made 1 and the terminal voltage can be kept constant by adjusting the field current. Almost the same power factor can be obtained. However, these power factor improvement methods have no power factor improvement effect because they are difficult to control when the output frequency exceeds approximately 30 Hz. For example, when operating a 4-pole synchronous motor, they cannot be used when the maximum speed is 900 rpm or more. Therefore, it was not possible to improve the power factor of the power supply.

[0007]

[Problem to be Solved by the Invention] When power factor correction control is applied to the cycloconverter by adopting trapezoidal wave control or neutral point AC bias method, when the maximum output frequency is 30Hz or less, the power transformer Since the secondary voltage of can be lowered, the generated reactive power is reduced,
The power factor of the power source can be increased. However, since these power factor improvement methods cannot be applied when the output frequency exceeds 30 Hz, it is not possible to reduce the reactive power even in an operating range where the operating frequency is 30 Hz or less. Especially when driving the main rolling machine, the motor rating is JEM11.
57, the overload rated output is the largest at the base speed, and the reactive power generated by the cycloconverter is also the largest at the base speed and lower speeds.

The present invention can provide a method and apparatus for operating a synchronous motor using a cycloconverter, which can suppress the maximum generated reactive power and reduce the power supply voltage drop even when the maximum frequency exceeds 30 Hz.

[0009]

[Means for Solving the Problems] A method of operating a synchronous motor using a cycloconverter according to the present invention provides a method for operating a synchronous motor by controlling the cycloconverter using trapezoidal wave control or a neutral point AC bias method. The cycloconverter is controlled by trapezoidal wave control or a neutral point AC bias method only when the output frequency is an operating frequency that operates the synchronous motor at a predetermined speed or less, and the output frequency of the cycloconverter controls the synchronous motor at a predetermined speed. When the operating frequency exceeds the operating frequency, the field of the synchronous motor is weakened to lower the terminal voltage.

Further, the synchronous motor operating device using the cycloconverter of the present invention includes a synchronous motor, a cycloconverter provided in the power supply circuit of the synchronous motor, and a trapezoidal wave control or neutral point AC bias method for controlling the cycloconverter. The control device includes a detection means for detecting the operating frequency of the synchronous motor, and a detection signal of the detection means is inputted so that the output frequency of the cycloconverter drives the synchronous motor at a predetermined speed or less. A first control means for controlling the cycloconverter by trapezoidal wave control or a neutral point AC bias method only when the cycloconverter is operated at an operating frequency of and second control means that weakens the field of the synchronous motor and lowers the terminal voltage when the operating frequency of the motor exceeds a predetermined speed.

[0011]

[Function] According to such a method and device for operating a synchronous motor using a cycloconverter, reactive power can be reduced when the synchronous motor operates at a frequency below a predetermined speed (30 Hz or less), and when the synchronous motor reaches a predetermined speed. When the operating frequency exceeds 30 Hz, the terminal voltage is lowered to suppress the maximum generated reactive power, thereby reducing the power supply voltage drop.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a control block in which a neutral point AC bias method is applied to a synchronous motor operation system using a cycloconverter. In FIG. 1, 1 is a synchronous motor (SM) equipped with an armature winding A and a field winding F.
), the armature windings A of each of the three phases of this synchronous motor 1 are connected to a power transformer 3 via a cycloconverter 2 of a neutral point AC bias type.

A speed detector 4 is installed in the armature A of the synchronous motor 1.
and a magnetic pole detector 5 are respectively attached. The speed detector 4 detects the rotational speed of the synchronous motor 1, and its speed detection signal is compared with a speed reference n* as a speed feedback signal nFB, and the deviation thereof is provided to the speed controller 6. Further, the speed feedback signal nFB is given to the field weakening reference generating section 7 and the frequency detecting section 8, respectively.

Further, reference numeral 9 denotes a current detection section that detects the armature current of the synchronous motor 1 via a current transformer 10, and the armature current detected by this current detection section 9 is given to a coordinate conversion section 11. Here, in synchronization with the magnetic pole position signal detected by the magnetic pole position detector 5, a q-axis component Iq and a d-axis component Id expressed as rectangular coordinate components are obtained from the armature current and are added to the magnetic flux calculation section 12. This magnetic flux calculation section 12 has a current transformer 13
The field current If detected by the field current detection section 14 is inputted via the field current detecting section 14. The magnetic flux calculation unit 12 calculates the q-axis component Iq, the d-axis component Id, and the field current I input from the coordinate conversion unit 11.
The internal operation angle δ and magnetic flux Φ are determined from f, and the output IT obtained by dividing the output of the speed control unit 6 by the magnetic flux Φ determined here is given to the armature current control unit 15.

Furthermore, the armature current control section 15 has the deviation ΔΦ between the magnetic flux reference Φ* generated by the field weakening reference generation section 7 and the magnetic flux Φ determined by the magnetic flux calculation section 12, and the operating angle δ.
is input. The armature current control section 15 controls these outputs I
The q-axis component Iq* and the d-axis component Id* of the armature current reference are determined based on T, the magnetic flux deviation ΔΦ, and the operation angle δ. The q-axis component Iq* and d-axis component Id* of the armature current reference obtained by the armature current control section 15 are the same as the q-axis component Iq and d-axis component Id of the armature current obtained by the coordinate conversion section 11, respectively. They are compared and the deviation is given to the current control section 16. When the current control unit 16 receives the deviations of the q-axis Iq and d-axis Id of the armature current from the armature current reference, it calculates the q-axis Vq and d of the output voltage reference for current control.
The axis portion Vd is given to the coordinate transformation section 17. This coordinate conversion section 1
7 creates a three-phase output standard using the q-axis component Vq and the d-axis component Vd given by the current control section 16 in synchronization with the detection signal of the magnetic pole position detector 5, and uses the triple frequency generation section 18 on this three-phase output standard. The output generated in synchronization with the detection signal of the magnetic pole position detector 5 is superimposed and given to the phase control section 19 that controls the cycloconverter 2. The triple frequency generator 18 is controlled by the frequency detection signal of the frequency detector 8,
Until the frequency detected by the frequency detection unit 8 reaches a certain frequency f1, a triple harmonic of a certain amplitude is generated, and when the frequency reaches f1, the amplitude of the triple harmonic decreases, and when it becomes higher than the frequency f1, a triple harmonic is generated. The amplitude of the wave is set to zero.

On the other hand, 20 is a field current into which the magnetic flux reference Φ* generated by the field weakening reference generation section 7 and the q-axis component Iq and d-axis component Id of the armature current obtained by the coordinate conversion section 11 are respectively input. In the reference calculation unit, this field current reference calculation unit 20 calculates these magnetic flux references Φ* and q of the armature current.
Field current reference If* based on axis Iq and d-axis Id
This is what we seek. In addition, when the frequency detected by the frequency detection section 8 reaches a certain frequency f1, the field current reference calculation section 20 uses the detection signal at that time as a field current reference to weaken the field, and the field current reference calculation section 20 sets the field current reference to weaken the field by the detection signal at that time. 30H
When the frequency f2 reaches z or lower, it is output as a field current reference that stops field weakening. This field current reference If* is compared with the field current If detected by the field current detection section 14, and the deviation thereof is given to the field current control section 21. The field current control section 21 controls the field current by applying the deviation to a phase control section 23 of a thyristor rectifier 22 provided as a field power source in the field circuit of the synchronous motor 1. Next, the operation of the synchronous motor operating system configured as described above will be described.

Assuming that the synchronous motor 1 is now operating at the base speed, the operating frequency at this time is normally 3.
It is below 0Hz. Control in such a state is as follows.

Speed control is performed by the speed controller 6 based on the deviation between the speed feedback signal nFB detected by the speed detector 4 and the speed reference n*, and the output IT is converted by the coordinate converter 11 using the magnetic flux calculator 12. The q-axis component Iq and d-axis component Id of the armature current and the field current detection unit 14
The internal operation angle δ determined based on the field current If detected in is input to the armature current control section 15. In this armature current control section 15, the output IT and the internal operation angle δ
From the q-axis Iq* and d-axis Id* of the armature current reference
seek. The q-axis component Iq* and the d-axis component Id* of this armature current reference
is the q-axis component Iq of the armature current converted by the coordinate conversion unit 12
and d-axis component Id, and when the deviation is given to the current control section 16, current control is performed and output voltage reference q-axis component Vq and d-axis component Vd are output. When the q-axis component Vq and the d-axis component Vd are input to the coordinate conversion section 17, the coordinate conversion section 17 obtains a three-phase output voltage reference.

On the other hand, at this time, the frequency detector 8 detects that the operating frequency of the synchronous motor 1 is below 30 Hz, so the triple frequency generator 18 generates triple harmonics of a certain amplitude. . Therefore, this third harmonic is superimposed on the three-phase output voltage reference output from the coordinate conversion section 17 and is given to the phase control section 19, so that the control delay angle of the cycloconverter 2 is controlled.

As shown in FIG. 2, the phase output voltage at this time becomes almost a trapezoidal wave C when the triple harmonic A is superimposed on the sine wave B, and the peak voltage is lower than the sine wave output B, so the cycloconverter The secondary voltage of the power transformer 3 of No. 2 can be made lower than when outputting a sine wave. In this case, the neutral points of the synchronous motor 1 and the cycloconverter 2 are not connected, so
The line voltage of the synchronous motor 1 becomes a sine wave as shown in FIG. 3, and no ripple occurs.

Next, when the frequency detection section 8 detects that the operating frequency of the synchronous motor 1 has reached a certain frequency f1, the detection signal causes the amplitude of the triple harmonic generated by the triple frequency generation section 18 to be reduced. In addition, the field current reference calculating section 20 obtains a field reference in order to weaken the field. Further, when the frequency detection unit 18 detects that the operating frequency of the synchronous motor 1 is higher than a certain frequency f1 and reaches a frequency f2 of approximately 30 Hz or lower, the detection signal causes the triple frequency generation unit 18 to generate The amplitude of the harmonic is set to 0, and the field current reference calculation unit 20 calculates a field current reference in order to stop the weakening of the field.

The motor terminal voltage resulting from the above control is as shown in FIG. That is, since the frequency when the synchronous motor 1 is operated at a synchronous speed is usually less than f1,
Reactive power can be suppressed by neutral point AC bias control, and neutral point bias control does not operate above f2, but in the case of a JEM1157 compliant rolling main machine electric motor, the overload capacity is limited as shown in Figure 5 b. Because it is small, the reactive power is not much larger than that below the base speed. Here, in FIG. 5, a indicates the rated output, c indicates the generated reactive power when the present invention is not applied, and d indicates an example of the tendency of the generated reactive power when the present invention is applied.

As described above, in this embodiment, when the cycloconverter 2 is controlled by the neutral point AC bias method to operate the synchronous motor 1, the output frequency of the cycloconverter 2 is such that the synchronous motor 1 is operated at a predetermined speed or less. The cycloconverter 2 is controlled by the neutral point AC bias method only when the operating frequency is reached, and the field of the synchronous motor 1 is weakened when the output frequency of the cycloconverter 2 reaches an operating frequency that causes the synchronous motor 1 to exceed a predetermined speed. Since the terminal voltage is lowered by lowering the terminal voltage, reactive power can be reduced when the operating frequency of the synchronous motor 1 is 30 Hz or less, and when the operating frequency of the synchronous motor 1 exceeds 30 Hz, the terminal voltage is lowered to reduce the maximum generated power. By suppressing reactive power,
Power supply voltage drop can be reduced.

In the above embodiment, the case where the cycloconverter 2 is controlled by the neutral point AC bias method has been described, but the same effects as described above can be obtained even when the phase voltage trapezoidal wave control is applied. . Further, in the above embodiment, the frequency detection unit 8 detects the operating frequencies f1 and f2 of the synchronous motor 1, but this operating frequency f
1 and f2, the motor terminal voltage Va may be detected.

[0025]

[Effects of the Invention] As described above, according to the present invention, when the operating frequency of the synchronous motor is 30Hz or less, reactive power can be reduced, and when the operating frequency of the synchronous motor exceeds 30Hz, the terminal voltage can be reduced. Since the maximum generated reactive power is suppressed, it is possible to provide a method and apparatus for operating a synchronous motor using a cycloconverter, which can reduce the power supply voltage drop.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a synchronous motor operating system according to an embodiment of the present invention.

FIG. 2 is a phase voltage waveform diagram when neutral point AC bias control is applied in the same embodiment.

FIG. 3 is a diagram of the motor line voltage waveform at that time.

FIG. 4 is a diagram showing the relationship between motor frequency and terminal voltage in the same embodiment.

FIG. 5 is a diagram showing an example of the output characteristics of a rolling main machine motor conforming to JEM1157 and trends in generated reactive power when the present invention is applied and when the present invention is not applied.

[Explanation of symbols]

1...Synchronous motor, 2...Cycloconverter, 3...
Power transformer, 4...Speed detector, 5...Magnetic pole position detector, 6...Speed control section, 7...Field weakening reference generation section, 8
... Frequency detection section, 9 ... Current detection section, 10 ... Current transformer, 11 ... Coordinate transformation section, 12 ... Magnetic flux calculation section, 13 ...
Current transformer, 14... Field current detection section, 15... Armature current control section, 16... Current control section, 17... Coordinate conversion section, 1
8...Triple frequency generation section, 19...Phase control section, 20...
...Field current reference calculation section, 21...Field current control section, 22
...Thyristor rectifier, 23...Phase control section.

Claims (2)

[Claims] 1. A method for operating a synchronous motor by controlling a cycloconverter using trapezoidal wave control or a neutral point AC bias method, wherein the output frequency of the cycloconverter is lower than the operating frequency at which the synchronous motor is operated at a predetermined speed or less. Only when the cycloconverter is controlled by trapezoidal wave control or neutral point AC bias method, and when the output frequency of the cycloconverter reaches an operating frequency at which the synchronous motor is operated at a speed exceeding a predetermined speed, the field of the synchronous motor is weakened. A method of operating a synchronous motor using a cycloconverter, characterized in that the terminal voltage is reduced by using a cycloconverter. 2. A synchronous motor, a cycloconverter provided in a power supply circuit of the synchronous motor, and a control device that controls the cycloconverter by trapezoidal wave control or a neutral point AC bias method, the control device a detection means for detecting the operating frequency of the synchronous motor;
A first control unit that controls the cycloconverter by trapezoidal wave control or neutral point AC bias method only when the detection signal of the detection means is input and the output frequency of the cycloconverter is an operating frequency at which the synchronous motor is operated at a predetermined speed or less. and a detection signal from the detection means is input, and when the output frequency of the cycloconverter reaches an operating frequency at which the synchronous motor is operated at a speed exceeding a predetermined speed, the field of the synchronous motor is weakened to lower the terminal voltage. A driving device for a synchronous motor using a cycloconverter, characterized in that it is equipped with a second control means.