JPH0311197B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Description of the technical field The present invention relates to an improvement of an induction motor control device for a railway vehicle.

(b) Description of the Prior Art The use of an induction motor as the main motor of a railway vehicle has great advantages in terms of size, weight reduction, and maintenance-free operation. In order to efficiently control the speed of an induction motor, variable voltage, variable frequency control (hereinafter abbreviated as VVVF) is required, and a VVVF inverter using a thyristor or the like is usually used. Fig. 1 shows the equivalent circuit for one phase of the induction motor and the relationship between the VVVF inverter and the input filter, where 20 is the input filter reactor Lo, 21 is the input filter capacitor Co,
22 is the VVVF inverter, 23 is the primary leakage inductance L ₁ , 24 is the primary resistance R ₁ , 2
5 is the excitation inductance Lm, 26 is the secondary leakage inductance L ₂ , 27 is the equivalent secondary resistance
R ₂ /S. Here, S is the slip of the induction motor and is defined as follows.

S = Slip frequency (FS) / Inverter output frequency (F) This VVVF method requires advanced control technology because the control itself is complex and PWM modulation must be performed to reduce power supply harmonics. is required.

Conventionally, a method as shown in FIG. 2 has been used as a control section of such a PWM modulation VVVF inverter.

FIG. 2 is a block diagram showing the control section of a conventional VVVF inverter. 1 is a pulse generator that detects the rotation speed, 2 is a rotation frequency calculation section that calculates the rotation frequency _FR from the pulse generator signal, 3 is a slip/skid detection unit that detects slipping and skidding based on the time rate of change of the pulse generator signal; 4;
5 is the master controller and brake valve that gives the travel command MC and notch command P/B, 5 is the master controller command
A current command value calculation unit that calculates a current command value IC according to the MC, variable load VL, and slipping and sliding condition WSD;
Reference numeral 6 indicates a power running regeneration discrimination unit that discriminates between power running P and regeneration B based on the notch command P/B, and 7 indicates a current command value IC, P or B conditions, and a current deviation IU between the current command value IC and the current IM of the induction motor. 8 is the inverter frequency F, which calculates the reference slip frequency FS1 and the slip frequency FS according to
and a modulation rate calculation unit that calculates the modulation rate AL from the overhead line voltage EC; 9 a modulation pulse mode calculation unit that calculates the modulation pulse mode N from the inverter frequency F;
And 10 is PWM according to inverter output frequency F, modulation pulse mode N and modulation rate AL
This is a PWM modulation section that performs modulation.

FIG. 3 shows the details of the slip frequency calculation section 7 shown in FIG. 2, and shows the reference slip frequency FS1 given as the output of the function unit 11 which inputs the current command value IC and the first-order lag of the current deviation IU. The sum of the constant current corrected slip frequencies FS2 given as the output of the compensator 12 is passed through the limiter 13 and then output as the slip frequency FS. This allows IC
Constant current control called IM is performed.

In Figure 1, the input filter reactor Lo
The damping element for the oscillating current (hunting current) that attempts to flow between the input filter circuit composed of the input filter capacitor Co and the reactance Lm on the induction motor side is the primary damping element in series. There are only the resistor R ₁ and the equivalent secondary resistor R ₂ /S that are connected in parallel, and in principle, the larger R ₁ and the smaller R ₂ /S, the greater the damping effect. However, the value of R ₁ is very small, and conversely, the value of S of R ₂ /S is small to begin with, and S becomes even smaller as the inverter frequency F becomes higher, so we cannot expect a large damping effect with both of them alone. I can't. Therefore, if VVVF control is performed while simply performing constant current control using the slip frequency FS as shown in Figures 2 and 3, if an oscillating current occurs in the main circuit, it will be difficult to stabilize it. I couldn't do it.

(c) Purpose of the Invention The present invention has been made in view of the above points, and provides an induction motor that prevents oscillating current in the main circuit when the induction motor is subjected to slip frequency control using a VVVF inverter by correcting the slip frequency. The present invention provides a control method.

(d) Structure of the Invention FIG. 4 is a block diagram showing an embodiment of the control section of the VVVF inverter of the present invention, and the structure is the same as that of FIG. 2 except for the slip frequency calculation section 17.
Also, FIG. 5 shows the details of the slip frequency calculation section 17 in FIG. 4, and the structure shown in FIG.
A differential compensator 14 and a switch 15 for reversing the polarity during power running and regeneration are added.

(e) Effect of the invention The VVVF inverter can independently control the AC output voltage EM and the slip frequency FS, and as shown in the control characteristic diagram in FIG. 6, they are each controlled as follows.

That is, in the range from the point F1 where the output frequency F is 0 to the point _F1 where the AC output voltage EM is saturated, as shown in Figure 6, where the AC output voltage EM and the output frequency F of the VVVF inverter are in a proportional relationship, the AC output voltage EM and the output frequency F are in a proportional relationship. Both the slip frequency FS can be controlled, and the current command value IC and the induction motor current IM are controlled to be equal.
When the VVVF inverter output frequency F exceeds the above F ₁ and the slip frequency of the induction motor is controlled, in the range of the VVVF inverter output frequency F ₂ which corresponds to the maximum slip frequency FS that can control the slip frequency,
The AC output voltage EM outputs the maximum value, the slip frequency FS is controlled, and the current command value IC and the current IM of the induction motor are controlled to be equal as described above,
In the range where the VVVF inverter output frequency F exceeds the above _F2 , the AC output voltage EM, the slip frequency FS
Both have a constant maximum value, and the current IM of the induction motor is controlled to be less than the current command value IC.

In a VVVF inverter, the method usually considered as a method to strengthen the damping of vibration phenomena is to use negative feedback of the differential element of the current IM of the induction motor, as is done in general converters, to increase the AC output voltage EM of the VVVF inverter. This is a method of adding it to the modulation rate AL, which is a control parameter. This method increases R ₁ in an apparent transient manner only for the oscillating current in Figure 1, and is applicable not only to control converters that vary the voltage, that is, VVVF inverters, but also to chopper devices, phase control rectifiers, CVCF inverters, etc. However, it is a commonly effective method,
This method is shown in Figure 6 for a VVVF inverter.
Since it is applicable only in the range where the output frequency F of the VVVF inverter is in the range of 0 to _F1 , the anti-hunt effect is naturally lost in other ranges.

Therefore, the present invention focuses on the slip frequency FS, which is a control element specific to VVVF inverters, and changes and controls the parallel resonance conditions to realize anti-hunt. Specifically, anti-hunt is achieved by the following effects. It is done. In other words, as mentioned above in Fig. 1, it is sufficient to temporarily reduce the secondary equivalent resistance R ₂ /S, which is another element for strengthening damping, only with respect to the oscillating current. The steady value is the reference slip frequency FS1 based on the current command value IC shown in Figure 3 to equalize the current command value IC and the current IM of the induction motor, and the constant current correction slip frequency of the first-order lag compensation of the current deviation IU. Since it is determined by the constant current control element that is the sum of FS2, the slip frequency is determined only for the oscillating current superimposed on the induction motor current IM, that is, the change in the induction motor current IM.
All you have to do is add an element to adjust the FS.

The oscillating current component △IM of the current IM of the induction motor is
Since the input filter capacitor 21 is always charged and discharged through the input filter capacitor Co21, this current can be detected by installing an AC current transformer ACCT on the connection line of the input filter capacitor 21, but in this case, ACCT and The number of detection input circuits increases.

Therefore, in the present invention, ΔIM is detected by the following method. There is a relationship between ΔIM and the oscillating component ΔEC of the voltage of the input filter capacitor 21 as shown in the following equation.

△EC=1/Co∫△IM・dt Also, if the DC component of the voltage of the input filter capacitor 21 is ECo, the voltage EC of the input filter capacitor 21 is EC=ECo+△EC, and when differentiated, dEC/dt =d(ΔEC)/dt=ΔIM/Co, and by differentiating the voltage of the input filter capacitor 21, the oscillating current component ΔIM of the current IM of the induction motor can be obtained.

The method of realizing damping reinforcement by using the slip frequency is the method shown in FIG.
By differentiating the electric current EC of the input filter capacitor 21, a differential element that is a slip frequency correction element can be obtained. During power running, this differential element FS3 is set to the reference slip frequency FS1 by the switch 15.
By adding to the sum of constant current correction slip frequency FS2, input filter capacitor 21
When the voltage EC tries to increase, R ₂ /S becomes smaller, and the excitation inductance Lm shown in Fig. 1
On the other hand, when the voltage EC of the input filter capacitor 21 attempts to decrease, R ₂ /S increases and acts to prevent the current flowing through the excitation inductance Lm from decreasing. This action attempts to keep the current in the excitation inductance Lm constant even if an oscillating current occurs in the current IM of the induction motor. In other words, the oscillating current is absorbed by a transient change in the equivalent secondary resistance. Large damping acts only on the oscillating current without affecting the fact that the current command value IC and the current IM of the induction motor are equal and have constant current characteristics.

In the case of power running, power is supplied from the power supply side, so the fluctuations in the current IM of the induction motor and the fluctuations in the voltage EC of the input filter capacitor Co provided at the inverter input are in opposite phase, so the input filter capacitor Co When the voltage EC of the input filter capacitor 21 is about to rise, a differential element of the voltage EC of the input filter capacitor 21 is added by positive feedback to suppress the rise by reducing R ₂ /S. However, in the case of electric power regenerative braking, Conversely, since the power is returned to the power source, the fluctuations in the current IM of the induction motor and the fluctuations in the voltage EC of the input filter capacitor Co21 are in the same phase, and therefore the voltage of the input filter capacitor 21 is
By adding the EC differential element through negative feedback, exactly the same damping effect as in power running can be obtained.

(f) Effects of the Invention As explained above, according to the present invention, the oscillating current of the main circuit current that occurs when an induction motor is driven by a VVVF inverter with an input filter under slip frequency control, and the constant current control performance can be improved. It can be easily stopped without any damage.

[Brief explanation of drawings]

Figure 1 shows the equivalent circuit for one phase of an induction motor.
A diagram showing the relationship between a VVVF inverter and an input filter, FIG. 2 is a block diagram of a conventional VVVF inverter control section, FIG. 3 is a block diagram of the slip frequency calculation section of FIG. 2, and FIG. 4 is a block diagram of a conventional VVVF inverter control section. FIG. 5 is a block diagram of the slip frequency calculation section of FIG. 4, and FIG. 6 is a control characteristic factor diagram. 7...Slip frequency calculation unit, 14...Differential compensator, 15...Switch, 17...Slip frequency calculation unit, 21...Input filter capacitor.

Claims (1)

[Scope of Claims] 1. A variable voltage/variable frequency inverter that controls the frequency of an induction motor; an input filter capacitor provided on the input side of the variable voltage/variable frequency inverter; and a rotational frequency detector that detects the rotational frequency of the induction motor. current command calculating means for calculating the current command of the induction motor; frequency command calculating means for calculating the slip frequency command from this current command; differentiating means for differentiating the voltage of the input filter capacitor; without changing the polarity of the output of the means,
In the case of brakes, there is a switch that inverts the polarity of the output of the differentiating means, and the output frequency of the variable voltage/variable frequency inverter is calculated by adding the output of this switch, the slip frequency command, and the output of the rotation frequency detector. A control device for an induction motor, comprising an output frequency calculation means.