JPH0239162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for an induction motor for a vehicle.

The use of an induction motor as a main motor for a railway vehicle has great advantages in terms of size, weight reduction, and maintenance-free nature.

By the way, in order to efficiently control the speed of an induction motor, variable voltage and variable frequency control (hereinafter referred to as variable frequency control) is required.
VVVF (VVVF) is required, and VVVF inverters using thyristors are usually used.
This VVVF method requires advanced control technology because the control itself is complex and PWM modulation must be performed to reduce power harmonics.

Conventionally, a configuration as shown in FIG. 1 has been adopted as a control section of such a PWM modulation VVVF inverter.

Figure 1 shows the control section of the VVVF inverter as a block circuit, where 1 is a pulse generator that detects the rotation speed of the induction motor, and 2 is a rotation frequency calculator that calculates the rotation frequency FR from the signal of pulse generator 1. 3 is a slipping and skidding detection unit that detects slipping and skidding based on the time rate of change of the signal of the pulse generator 1; 4 is a master controller and brake valve that gives a running command MC and a notch command P/B;
5 is a current command value calculation unit that calculates a current command value IC according to the mass controller command MC, variable load VL, and slipping and sliding condition WSD; 6 is a power running regeneration unit that determines power running P and regeneration B based on the notch command P/B A discrimination section, 7 is a slip frequency calculation section that calculates the slip frequency FS from the current command value IC and the conditions of power running P or regeneration B, and 8 is a slip frequency calculation section that controls the output voltage according to the current deviation IU between the current command value IC and the motor current IM. Modulation rate for
9 is a modulation pulse mode calculation unit that calculates modulation pulse mode N from inverter frequency F, and 10 is inverter output frequency F, modulation pulse mode N, and modulation rate AL.
This is a PWM modulation section that performs PWM modulation according to the following.

Now, the torque T of the induction motor is the slip frequency FS
In a small range, it can be approximately given by T=K ₁・(IM) ²・r ₂ /FS (where r ₂ is the secondary resistance of the motor). In the control circuit shown in Figure 1, the slip frequency FS is uniquely determined by the current command value IC,
It is unrelated to the transient phenomenon of the motor current IM, and constant current control called ICIM is performed by providing an appropriate feedback compensation circuit in the modulation factor calculating section 8, so it is clear from the formula that the speed will change as long as r ₂ does not change. It is possible to obtain acceleration/deceleration performance with constant torque regardless of the torque.

However, in reality, _r2 is the resistance of the motor's rotor, so it generates a large amount of heat during operation.
Therefore, fluctuations in resistance due to temperature rise are unavoidable, and therefore constant torque characteristics as described above cannot be expected. In addition, in this method, the overhead line voltage EC
Since all transient phenomena caused by fluctuations in the modulation rate are absorbed by the constant current control loop of the modulation factor calculation section 8, this control loop is required to have extremely quick response, and therefore it is not easy to design the characteristics to ensure the stability of the loop. There was a drawback.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an induction motor control device that eliminates torque fluctuations due to temperature changes in the secondary resistance of the induction motor, and is stable and easy to design characteristics. .

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a block circuit according to an embodiment of the present invention, and the same parts as those in FIG. 1 are given the same symbols and their explanation will be omitted, and only the different points will be described here. In this embodiment, as shown in FIG. 2, the slip frequency calculation unit 7 in FIG. A calculation unit 17 is provided, and a modulation rate calculation unit 18 that calculates the modulation rate AL from the inverter frequency F and the overhead wire voltage EC in place of the modulation rate calculation unit 8 in FIG.
The configuration is such that the following is provided.

Next, the operation of the present invention will be explained using FIG. 2.

In FIG. 2, the output pulses of the pulse generator 1 are taken into a rotational frequency calculating section 2 and counted to determine the rotational frequency FR. At the same time, this pulse is taken into the slipping/sliding detection section 3,
Slipping and skidding WSD are detected by the time change in the number of pulses. The current command value calculation unit 5 calculates the MASCON command.
A current command value IC is calculated according to MC and variable load VL, and when the slipping and sliding conditions WSD are high, the command value is reduced. The power running regeneration determining section 6 determines whether power running P or regeneration B is selected based on the notch command P/B and outputs the result. The slip frequency calculation unit 17 calculates the current command value.
A constant term FS1 uniquely determined by the IC and a transient term FS2 given according to the current deviation IU are added and output as a slip frequency FS. This can be expressed as an equation as follows.

FS=FS1+FS2...S1=(IC)...FS2=G(S)・(IC-IM)...When the motor voltage EM is constant, the slip frequency FS and motor current IM are in the small range of the slip frequency FS.
There is an approximate relationship between IM=K ₂・FS+K ₃ ..., so the transfer function G of the transient term RS2
If the compensation gain of (S) is set to a certain degree, ICIM is achieved due to the effect of the transient term FS2, and constant current control is performed using the slip frequency FS. In the modulation factor calculation section 18, when the secondary resistance r ₂ is constant r ₂ = r ₂₀ ,
Modulation that generates an appropriate output voltage EM according to the inverter output frequency F according to a pre-calculated and memorized pattern to exhibit constant torque characteristics in the entire speed range under the conditions of IM = IC and FS = FS1. Calculate the rate AL. Furthermore, at this time, the overhead line voltage EC is detected, and even if this overhead line voltage EC fluctuates, the output voltage remains unchanged.
The modulation rate AL is computationally controlled so that EM does not change.

Therefore, here, the torque T when r ₂ = r ₂₀ is constant
is given by T= _K1・(IM) ²・_r2 /FS= _K1・(IC) ²・_r20 /FS1... The meaning of this equation is that when r ₂ = r ₂₀ , the slip frequency FS at which IM = IC in equilibrium is FS = FS1
It shows that. Therefore, now the resistance value of r ₂ increases by K ₄ times due to temperature rise and FS becomes FS=
Assuming that FS1 does not change, the equivalent secondary resistance r ₂ ′ is given by r ₂ ′=r ₂ /FS..., so r ₂ ′ increases and IM decreases. This state indicates an open loop state in which the loop of transient term FS2 does not act, and the transient term
When the loop of FS2 acts, the transient term FS2 has a certain positive value so that IMIC, and the FS at this time
= FS1 + FS2 should satisfy the following formula r ₂ ′ = K ₄ · r ₂₀ /FSr ₂₀ /FS1 ..., and in the end it will be controlled so that FS = K ₄ · FS1 .... That is, the torque T is given by T=K・(IM) ²・r ₂ ′... In this control method, r ₂ ′ is controlled to be constant, so even if r ₂ changes, the torque does not change.

Also, the modulation rate calculation section 18 is required to have quick response.
Basically, the slip frequency calculating section that performs feedback control only needs to compensate for the variation in r ₂ , so a very fast response is not required.

As described above, according to the present invention, it is possible to eliminate torque fluctuations due to temperature changes in the secondary resistance of the induction motor, and to provide a control device for an induction motor that is stable and whose characteristics can be easily designed.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a control section of a VVVF inverter constituting a conventional control device for an induction motor for a railway vehicle, and FIG. 2 is a block circuit diagram for explaining an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Pulse generator, 2...Rotation frequency calculation section, 3...Slip and skidding detection section, 4...Mascon, brake valve, 5...Current command value calculation section, 6...
...Power running/regeneration discrimination section, 17...Slip frequency calculation section, 18...Modulation rate calculation section, 9...Modulation pulse mode calculation section, 10...PWM modulation section.

Claims (1)

[Claims] 1. A pulse width modulation type variable voltage/variable frequency control inverter device for driving a vehicle induction motor, an inverter frequency signal and a modulation rate signal being input to the inverter device for pulse width modulation control. pulse width modulation means for providing a gate pulse of; rotational frequency calculation means for calculating a rotational frequency proportional to the rotational speed of the motor; and current deviation calculation means for calculating a deviation between a detected motor current value and a command value of the motor. means, a slip frequency calculating means for determining a slip frequency based on the deviation calculated by the current deviation calculating means and the command value of the motor current, and the slip frequency calculated by the slip frequency calculating means and the rotational frequency calculating means. An inverter frequency calculation means calculates an inverter frequency signal based on the rotational frequency determined by and supplies it to the pulse width modulation means, and a modulation rate signal is generated using the inverter frequency signal from the inverter frequency calculation means and a voltage signal proportional to the overhead wire voltage. and a modulation factor calculation means for determining the pulse width modulation means and providing the modulation factor to the pulse width modulation means.