JPH0458242B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a running control device for an electric vehicle, in particular, a system for controlling a plurality of main induction motors using a single variable voltage/variable frequency inverter (hereinafter referred to as a VVVF inverter). This invention relates to an improvement of a control device for an electric vehicle to be driven.

[Conventional technology]

Conventionally, easy-to-control DC motors have been used for electric vehicle drive motors, but three-phase induction motors have recently been used due to the inability to eliminate flashover accidents and the weak points of commutator and brush maintenance. There is a strong intention to switch to electric motors.

A three-phase induction motor produces power running torque below synchronous speed and braking torque above synchronous speed.

Therefore, the output frequency of the VVVF inverter is
The speed of the electric vehicle, that is, the number of rotations of the three-phase induction motor, is detected and set to a value appropriate for that number of rotations.

When multiple three-phase induction motors are driven by one VVVF inverter, there is no established theory as to which rotational speed of the multiple three-phase induction motors should be used, which unnecessarily complicates the device. The present invention
Focusing on the characteristics of the VVVF inverter and three-phase induction motor, as well as the characteristics unique to electric vehicles, we aim to provide a simple, highly reliable, and high-performance electric vehicle control device.

In general, a three-phase induction motor has a sliding speed of S
The relationship between slip S and torque T is shown in FIG. Slip S=0 is the synchronous speed,
When the inverter frequency of the VVVF inverter is f, the rotation speed of the three-phase induction motor is N (rpm), 3
If the number of poles of the phase induction motor is P, it is expressed by the following formula (1).

N=120f/P...(1) In the inverter control of an electric vehicle, in order to generate the required acceleration torque, the inverter frequency is set at a synchronous speed slightly higher than the vehicle speed, that is, the rotational speed of the three-phase induction motor, at each instant. The phase induction motor is being driven. For example, in Figure 2, the slip to produce torque A is S ₁ . When multiple three-phase induction motors are driven by one VVVF inverter, even if the vehicle speed is the same and the wheel diameter is the same,
If there is slippage between the wheels and the rail, the slips will not be the same even with four electric motors, and the torques will be A, B, C, D, etc.

For this reason, when changing the inverter frequency of the VVVF inverter and detecting the vehicle speed or the rotation speed of the three-phase induction motor, the average value or the minimum value of the rotation speed of all electric motors is used. There are also cases where attached vehicles are equipped with speed detectors.

[Problem that the invention seeks to solve]

As mentioned above, the method of detecting the vehicle speed is based on the same concept as that used in conventional DC electric vehicles to detect vehicle slippage.

However, in VVVF inverter drive system,
The difference is that the frequency is changed while constantly detecting the vehicle speed. Even if the vehicle speed is the same and there is no idling, a slight difference in wheel diameter will cause a slight difference in the rotational speed of the three-phase induction motor. This is shown in FIG. In FIG. 3, the horizontal axis represents the rotational speed N, and the vertical axis represents the torque. Since the three-phase induction motor has shunt-winding characteristics, the torque difference due to the difference in wheel diameter is relatively large.

In Figure 3, the horizontal axis represents the rotation speed, but since multiple motors are operated by one VVVF inverter, the given frequencies are the same, that is, the synchronous speeds are also the same, and this is expressed as N ₀ . The slip S=0 in FIG. 2 corresponds to the rotational speed N ₀ in FIG. 3. Wheel diameters are managed within a certain range. Since the vehicle speed for each axle is the same for each axle, the size of the rotation speed is inversely proportional to the size of the wheel diameter if there is no slippage. Therefore, by compensating for the difference in wheel diameter rather than the rotation speed, You can know. However, what we originally want to control by knowing the speed difference is to reduce the torque when the vehicle is idling, and it is contradictory to know the wheel diameter difference from the rotation speed, assuming that there is idling. To solve this problem, the rotational speed difference during coasting may be stored to compensate for the wheel diameter difference. However, when driving a three-phase induction motor using a VVVF inverter, it is almost meaningless to compensate for the wheel diameter difference to detect slippage.

This is because, as mentioned above, in order to keep the torque difference small and to manage the wheel diameter difference small, the wheel diameter difference is originally small, and as shown in Figure 2, due to the shunt characteristics of the three-phase induction motor, A decrease in slip S caused by a slight slip causes a large change in torque, and there is little need to perform slip detection using differential speed detection. Nevertheless, it uses a large number of rotation speed detectors, is difficult to maintain, and requires complicated calculation processing.

[Means for solving problems]

The present invention provides that, in the case of VVVF inverter drive, the synchronous speed of the main induction motor is gradually increased as the rotational speed of the main induction motor increases, so that the operating speed (rotational speed) and synchronous speed (rotational speed) of the main induction motor This was done by focusing on phenomena such as the fact that the numbers (numbers) differ by only a few percent, the difference in wheel diameter of electric cars, and acceleration while slightly idling.

In other words, among the output voltage and frequency that can be changed for torque control during VVVF inverter operation,
At least the frequency command value ends up being a value with almost no difference between the average value and the minimum value for each wheel. Therefore, speed detection does not need to be performed on all axes, but only on the minimum number of axes, for example, two axes, necessary for failure detection. Even when two axes are detected, we do not use the average value, maximum, or minimum, but rather the axis that is likely to stick even if it is probabilistic (this is determined by the vehicle body design, and is almost determined by the direction of travel, power running, and braking, and can be selected) ) should be selected and used according to the driving conditions. This is because, as mentioned above, the difference in speed due to the difference in wheel diameter and the difference in speed due to wheel slipping are about the same, so we decided to specify the axle in advance and detect the speed.
It is more rational to issue a command speed.

Therefore, the present invention provides an electric vehicle in which a plurality of main induction motors are driven by one VVVF inverter, in which two or more motor rotation speed detectors are provided, and the outputs of the rotation speed detectors are compared with each other to detect a failure.
In addition to using a healthy detector output when detecting a failure,
When there are a plurality of healthy detectors, only one of the detector outputs is selected and used depending on the driving command state of the vehicle.

〔Example〕

The flowchart in FIG. 1 is a configuration diagram of a software system for selecting the output of a rotational speed detector, showing one embodiment of the present invention. PG ₁ and PG ₂ indicate rotation speed detectors. For example, in a system in which eight main induction motors are collectively controlled by one VVVF inverter, the motor rotation speed detection pulse generators provided on the second and third axes are designated as PG ₁ and PG ₂ . second axis,
The third axis is chosen because it is generally less prone to slipping and skidding than the leading axis. By comparing the output pulse trains of pulse generators PG ₁ and PG ₂ , it is determined whether both pulse generators are healthy or malfunctioning. There are various types of failures, and details of failure detection methods will be omitted here.

Next, the speed detector selection means X for electric vehicle travel control will be explained.

In Figure 1, in step 1 the pulse generator
PG ₁ and PG ₂ are compared, and as a result, a healthy pulse generator output is selected in step 2 and step 3. If both pulse generators are healthy, select according to running conditions in steps 4 to 6.
Select the pulse generator output of the shaft that is less likely to slip or skid. In the example shown in FIG. 1, the structure of the truck and car body is such that the second axis has a greater axle load than the third axis during power running, forward movement, and reverse movement under braking, and this is an example selected for design reasons.

〔Effect of the invention〕

In VVVF systems, PWM (pulse width modulation) control is generally used for voltage control because it is preferable for the main induction motor and reduces noise, and the firing phase of the thyristor must be controlled correctly. In these controls, it is becoming common for sequence control and PWM control to be digitally controlled by microcomputers. The performance of recent microcomputers is excellent, but as the inverter frequency increases,
The computation time is by no means sufficient.
Therefore, it is necessary to rationally configure the speed detection unit essential to the VVVF inverter system and minimize the calculation time for speed detection. , wasteful calculations such as minimum value calculations are prevented, and higher frequency and more accurate PWM control can be achieved.

Naturally, the reduction in the number of pulse generators reduces manufacturing and outfitting costs, and the reduction in the number of devices also reduces maintenance.

[Brief explanation of the drawing]

Fig. 1 is a software system configuration diagram for output selection of a rotational speed detector showing an embodiment of the present invention, Figs. 2 and 3 are speed-torque curve diagrams of the main induction motor, and Fig. 2 shows the slip FIG. 3 is a diagram showing speed in terms of rotational speed. PG ₁ , PG ₂ ...Rotation speed detector. X...Speed detector selection means.

Claims (1)

[Claims] 1. A speed detector and a speed detector selection means X,
A traveling control device for an electric vehicle, which has a plurality of main induction motors operated by one variable voltage/variable frequency inverter to control the traveling of the electric vehicle, and two or more speed detectors. The speed detector selection means X inputs the output signals of each speed detector, compares the output signals with each other to detect a failure, and selects a healthy speed detector when a failure is detected in a speed detector. However, when a failure is not detected, a predetermined speed detector is selected and used according to the driving condition.