JP2003143881A - Start controller for synchronous motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a start controller for synchronous motor which is capable of synchronizing a synchronous motor with reliability. SOLUTION: The start controller for synchronous motor is for controlling the excitation of a synchronous motor at start. The start controller comprises: a voltage detecting means which detects a voltage induced in the field winding of the rotor of the synchronous motor by generating revolving magnetic fields in the stator; a sampling means for sampling the detected voltage; a zero cross point detecting means which detects a zero cross point based on the sampled value of voltage; a sampled value selecting means which selects two sampled values on the positive or negative side, in proximity to the zero cross point; and an excitation timing determining means which computes a slip value based on the two selected sampled values and determined timing of current supply to the field winding from the slip value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous motor starting control device for controlling excitation at the time of starting a synchronous motor.

[0002]

2. Description of the Related Art When starting a synchronous motor, a starting control device known as a proper phase device is used as a device for smoothly performing synchronous pull-in. The starting control device is an indispensable device for a synchronous motor that starts a heavy load.

A conventional starting control device of this type is composed of an electronic circuit and determines the excitation timing from the change in the polarity of the voltage induced in the field winding. In order to do that, finer control was needed.

Further, since the electronic circuit is dedicated to the start control only, it is difficult to expand the interface with other controls, and it is difficult to take measures even if there is a problem with the synchronization pull-in.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a starting control device for a synchronous motor which can reliably pull in the synchronous motor.

Another object of the present invention is to provide a starting control device for a synchronous motor, which can facilitate the expansion of the interface with other controls.

[0007]

The structure of the present invention will be described below after explaining the principle of the present invention. The absolute value of the voltage induced in the field winding (also called the secondary winding) of the rotor by generating the rotating magnetic field in the stator at the time of starting is the product of the secondary rated voltage V ₂₀ and the slip value s. And its frequency is proportional to the product of the rated frequency F ₀ and the slip value s. That is, the frequency of the voltage induced in the field winding is s · F ₀ ,
It is a sine wave with an amplitude of s · V ₂₀ . In the vicinity of the zero-cross point where the polarity of this voltage changes, sin (s · F ₀ ) is s
Since it can be approximated by F ₀ , the induced voltage Vf of the field winding is expressed by the following equation. Vf = K · s · V ₂₀ · s · F ₀ = K · s ² · V ₂₀ · F ₀ (K: constant) (1)

The voltage values induced in the field windings at two points on the positive side or the negative side in the vicinity of the zero-cross point, which are obtained by sampling the voltage Vf at the sampling period Δt, are Vf1, respectively.
If Vf2 is set, these voltage values can be expressed by the following equations. Vf1 = K · s ² · V ₂₀ · F ₀ · 2 · Δt (2) Vf2 = K · s ² · V ₂₀ · F ₀ · Δt (3) Equation (3) is subtracted from this equation (2) Then, s ² is obtained to obtain the following equation. s ² = (Vf 1 −Vf ² ) / (K · V ₂₀ · F ₀ · Δt) (4)

Therefore, the slip value s can be calculated by the following equation. s = {(Vf1-Vf2) / (K · V ₂₀ · F ₀ · Δt)} ^1/2 (5)

From the slip value s, the frequency f and the period T of the voltage induced in the field winding can be obtained by the following equation. f = s · F ₀ (6) T = 1 / f (7) As is clear from this, the slip value s corresponds to the point when the polarity of the voltage induced in the field winding changes. Smooth synchronization can be achieved by starting the phase control of the exciter so as to start passing a current through the field winding with a time delay.

In this case, when the slip value s is large, it is also difficult to pull in the synchronization. Therefore, it is necessary to increase the exciting current in order to carry out the synchronization more smoothly. for that reason,
In order to change the exciting current of the exciter, the current value is determined according to the slip value s.

By providing the programmable logic controller with the arithmetic and processing functions described above, the interface with other controls can be easily expanded.

Therefore, in the invention according to claim 1, in a starting control device for a synchronous motor for controlling excitation at the time of starting the synchronous motor, a field winding of the rotor is generated by generating a rotating magnetic field in a stator of the synchronous motor. Voltage detection means for detecting the voltage induced in the line, sampling means for sampling the detected voltage, zero-cross detection means for detecting the zero-cross point based on the sampling value of the voltage, and the vicinity of the detected zero-cross point Sampling value selecting means for selecting two sampling values on the positive side or the negative side, and a slip value is calculated based on the selected two sampling values, and a current supply timing for the field winding is determined from the slip value. Excitation timing determining means, and an excitation timing determining means.

According to a second aspect of the present invention, in the starting control device for a synchronous motor according to the first aspect, the programmable logic controller has each function of a sampling means, a zero-cross detection means, a sampling value selection means, and an excitation timing determination means. It is characterized by having been done.

According to a third aspect of the present invention, in the starting control device for a synchronous motor according to the first aspect, the exciting current determining means for determining a larger exciting current as the calculated slip value increases. .

According to a fourth aspect of the present invention, in the synchronous motor start control device according to the third aspect, each function of the sampling means, the zero-cross detection means, the sampling value selection means, the excitation timing determination means and the excitation current determination means is provided. It is characterized by having it in a programmable logic controller.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail based on the preferred embodiments shown in the drawings. FIG. 1 is a block diagram showing a schematic configuration of a start-up control device for a synchronous motor according to the present invention, together with an application target. In FIG. 1, the synchronous motor 1 is composed of a stator 11 and a rotor 12 formed by winding a field winding 13. The field winding 13 is supplied with a direct current through a slip ring (not shown) and has a function of a permanent magnet. The rotor 12 is connected to a load (not shown). A phase controller 2 is provided for supplying a phase-controlled DC current to the field winding 13 so as to start and rotate this load at a predetermined speed. Since various types of the phase control unit 2 have been proposed and described in the literature, they are simply represented by a controlled rectifying element.

Then, in order to smoothly pull in the synchronous motor 1, the start-up control device, with respect to the field winding 13,
A voltage detection resistor 3 that is connected in parallel only at the time of starting and a voltage generated with the illustrated polarity at both ends of the voltage detection resistor 3, for example, a voltage of about 1 to 5 V at maximum is input to achieve electrical insulation, A low voltage proportional to the voltage generated in the voltage detection resistor 3 is output, for example, an insulation circuit 4 made of a photocoupler and the output voltage of the insulation circuit 4 are input, and calculation and processing are executed in a predetermined procedure. As a result, a programmable logic controller that outputs a phase control start signal as a current supply timing signal and an excitation amount signal given as an excitation current (including PL in the following description, including drawings).
Abbreviated as C) 5.

FIG. 2 shows an embodiment of the embodiment shown in FIG.
The functional block diagram corresponding to the detailed calculation and processing of the LC5 is shown together with the application target, and the components denoted by the same reference numerals as those in FIG. 1 respectively represent the same elements.
The insulating circuit 4 inside is omitted. Here, the PLC 5 detects the voltage induced in the field winding 13 of the synchronous motor 1,
A / D converting voltage detecting means 51, a sampling means 52 for sampling the detected voltage and storing the value in a memory, a zero cross detecting means 53 for detecting a zero cross point based on the voltage sampling value, and a zero cross. Sampling value selection means 54 for selecting two sampling values in the vicinity of a point, and a slip value is calculated based on the selected two sampling values, and the excitation for determining the current supply timing of the field winding from the slip value. The timing determining means 55 and the exciting current determining means 56 for determining the exciting current based on the calculated slip value are provided.

The operation of the present embodiment configured as described above will be described below with reference to FIG. 3 as well. First, when the rotor 12 is rotated by the rotating magnetic field of the stator, as shown in FIG. 3A, a slip voltage Vr caused by a slip is generated at both ends of the voltage detection resistor 3 and the PLC 5
Entered in. The voltage detection means 51 detects this voltage and converts it into a digital signal. Therefore, the sampling means 5
2 samples this digital signal at a period Δt and sequentially stores the value. FIG. 3B shows a sampling state in the vicinity of the zero cross point of the slip voltage Vr.

When the zero-cross detecting means 53 detects the zero-cross point based on the sampling value stored in the sampling means 52, the sampling-value selecting means 54 is closest to the zero-cross point, and further, it is 2 before the zero-cross.
One sampling value Vf1 and Vf2 is selected. In the vicinity of the zero-cross point, the sine wave changes substantially linearly, so the sampling values Vf1 and Vf2 are values proportional to the square of the slip value s.

Therefore, the excitation timing determining means 55 uses the sampling values Vf1 and Vf2 to execute the calculation of the equation (5) to obtain the slip value, and further,
The frequency f of the voltage induced in the field winding by the equation (6)
The period T is obtained from the equation (7), and with a time delay corresponding to the slip value s from the time when the field voltage phase changes,
For example, a phase control start signal is applied to the phase control unit 2 at the zero cross point B next to the A section in FIG.

If the slip value s is large, it becomes difficult to pull in the synchronization. When the slip value s exceeds a predetermined value, the exciting current determining means 56 applies to the phase controller 2 an exciting amount signal for increasing the exciting current corresponding to the slip value s.

Incidentally, if the rated secondary voltage is 2000 V, the rated frequency is 50 Hz, and the slip value s is 1%,
The voltage induced in the field winding 13 is 20 V and its frequency is 0.5 Hz. Here, if the sampling period Δt is 20 ms, 100 sampling values can be obtained in one period, and the phase interval to be sampled is 3.
It will be 6 degrees.

Thus, according to the present embodiment, the detection accuracy of the voltage induced in the field winding 13 in the vicinity of the zero cross point is sufficiently high, and the slip value calculated based on the two detected voltages. Is highly accurate, which allows the start timing of phase control to be determined with high accuracy.

Further, the voltage induced in the field winding 13 is set to P
The current is supplied to the LC5, the current supply timing of the field winding 13 is determined by the calculation and processing of the PLC5, and the exciting current is determined based on the slip value. Therefore, the exciting current and the phase can be changed by changing the program. It becomes easy to expand the interface with other controls, such as changing the control start time appropriately.

[0027]

As is apparent from the above description, according to the present invention, the synchronous motor can be reliably pulled in synchronously. Further, according to another invention, it is possible to easily expand an interface with another control.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a start-up control device for a synchronous motor according to the present invention, together with an application target.

FIG. 2 is a block diagram showing functions corresponding to detailed operations and processes of the programmable logic controller in the embodiment shown in FIG. 1 together with application targets.

FIG. 3 is a waveform diagram showing a voltage generated in a field winding in accordance with slip and a sampling state thereof in order to explain the operation of the embodiment shown in FIG.

[Explanation of symbols]

1 Synchronous motor 2 Phase control unit 3 Voltage detection resistor 4 insulation circuit 5 Programmable logic controller (PLC) 11 stator 12 rotor 13 field winding 51 voltage detection means 52 sampling means 53 Zero cross detection means 54 Sampling value selection means 55 Excitation timing determination means 56 Exciting current determining means

Claims (4)

[Claims] 1. A starting control device for a synchronous motor for controlling excitation at the time of starting the synchronous motor, wherein a voltage induced in a field winding of the rotor is generated by generating a rotating magnetic field in a stator of the synchronous motor. Voltage detecting means for detecting, sampling means for sampling the detected voltage, zero-cross detecting means for detecting a zero-cross point based on the sampling value of the voltage, positive side or negative side in the vicinity of the detected zero-cross point Value sampling means for selecting the two sampling values, and the excitation value determination for calculating the slip value based on the selected two sampling values and determining the current supply timing for the field winding from the slip value. A starting control device for a synchronous motor, comprising: 2. A start-up control device for a synchronous motor according to claim 1, wherein a programmable logic controller is provided with each of the functions of the sampling means, the zero-cross detection means, the sampling value selection means, and the excitation timing determination means. . 3. The start control device for a synchronous motor according to claim 1, further comprising an exciting current determining means for determining a larger exciting current as the calculated slip value is larger. 4. The programmable logic controller according to claim 3, wherein each function of said sampling means, zero-cross detection means, sampling value selection means, excitation timing determination means and excitation current determination means is provided in a programmable logic controller. Start control device for electric motor.