JPS627384A - Variable voltage variable frequency induction motor controller - Google Patents

Abstract

PURPOSE:To effectively operate an electric motor vehicle while avoiding the hunting vibration of the vehicle due to a motor torque pulsation of a fork lift truck by increasing a slip frequency and a motor applying voltage at light- load and extremely low-speed operation time. CONSTITUTION:When an induction motor 10 is operated at an extremely low speed, a slip frequency command fS is increased by the characteristic 100 of a slip frequency command generator 14 and the characteristic 102 of a modulation ratio calculator 16, a modulation ratio gamma is increased to increase each voltage command V. Thus, since the slip of the motor 10 is controlled to be increased at extremely low-speed operation time, the torque pulsation of the motor 10 is separated from the natural vibration frequency band of a fork lift truck. As a result, the hunting vibration of the truck due to the torque pulsation can be largely reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an induction motor side device that simultaneously controls voltage applied to an induction motor and its frequency.

(Background of the Invention) In the conventional device shown in Japanese Patent Publication No. 59-28146, etc., the sum of the motor rotational speed fo and the slip frequency fs is multiplied by the slip frequency fs, and the voltage applied to the motor is proportional to the multiplied value. This reduces the motor rotational speed fo and the slip frequency fs, and reduces the motor applied voltage when the induction motor is operating at low speed with a light load, and as a result, the torque unevenness of the induction motor is suppressed. Ta.

However, in conventional devices, the slip frequency when the induction motor is operated at low speed with light load depends only on the motor characteristics, and the induction motor operates at a low frequency (usually several H).
2), so when an electric vehicle with an induction motor as the drive source is operated at low speed with a light load, such as alignment operation using a foot-lift, the voltage is 6 times the motor current. There is a problem in that torque pulsations occur periodically, and the torque pulsations coincide with the vehicle's natural vibrations, causing hunting vibrations in the vehicle.

(Object of the invention) The present invention has been made in view of the above-mentioned conventional problems,
The purpose is to provide an ill-m device for a variable voltage variable frequency induction motor that does not generate hunting vibrations in an electric vehicle using the induction motor as a drive source even when the induction motor is operated at low speed under a light load. .

(Structure of the Invention) In order to achieve the above object, the present invention comprises: an accelerator command generation means for generating an accelerator command; a motor rotation speed detection means for detecting the rotation speed of an induction motor; and a slip frequency according to the motor rotation speed. A slip frequency command generating means for generating a command; a voltage command generating means for generating a voltage command according to the accelerator command and the motor rotation speed; and a slip frequency command increasing means for increasing the slip frequency command during slow operation of the induction motor. , and voltage command increasing means for increasing the voltage command during slow speed operation of the induction motor.

(Description of Embodiments) Hereinafter, preferred embodiments of the apparatus according to the present invention will be described based on the drawings.

In FIG. 1, an induction motor 10 is used as a driving source for a forklift, and its rotational speed is detected by a rotational speed detector 12.

The rotational speed fO of the induction motor 10 detected by the rotational speed detector 12 is given to the Suberi frequency command generator 14 and the modulation ratio calculator 16.

In the rough slip frequency command generator 14, a slip frequency command fs is obtained from the characteristic 100 using the motor rotational speed fo, and the slip frequency command fs is given to the adder 18.

The motor rotation speed fO is given to this adder 18, and by adding the two, a frequency command f (=fo+fs>) for the motor applied voltage is obtained.

Furthermore, the modulation ratio γ is determined from the characteristic 102 using the motor rotational speed fO in the modulation ratio calculator 16, and the modulation ratio T is provided to the multiplier 20.

The multiplier 20 is supplied with an accelerator command A from an accelerator command generator (consisting of a potentiometer that detects the amount of depression of the accelerator pedal) via a linear amplifier 22.

Roughly multiply the accelerator command A by the modulation ratio γ or the multiplier 20
The amplitude command V of the motor applied voltage obtained by the multiplication is given to the sine wave generator 26 together with the frequency command f of the adder 18.

This sine wave generator 26 generates a three-phase sine wave whose amplitude is determined by the amplitude command ■ and whose frequency is determined by the frequency command f.
8W are respectively applied to one comparison input.

The other comparison input of these comparators 28U, 28V, 28W (7) is the carrier signal (triangular wave) of the carrier generator 30.
are given respectively, and the comparators 28U, 28V, 28W
Now, a three-phase PWM signal is obtained.

These PWM signals are given to the inverter 32,
The inverter 32 converts the output voltage of the on-vehicle battery 34 into a three-phase AC voltage according to these PWM signals.

The AC voltages of each phase are controlled to have an amplitude corresponding to the voltage command V and a frequency corresponding to the frequency command f, and the induction motor O is driven and controlled by these AC voltages.

The drive control of the induction motor 10 is performed as described above, but when the induction motor 10 is operated at a slow speed, the characteristics 100 of the slip frequency command generator 14, the modulation ratio calculator 16
As understood from the characteristic 102 of the slip frequency command f
s is increased, and the modulation ratio T is increased so that the voltage command V
When the induction motor 10 is rotated at a very low speed in the full torque characteristic 104 of the induction motor 10 shown in FIG. 10 is originally operated, but
In this embodiment, the edge frequency command f.

is increased at that time, so that the induction motor 10 is operated at an operating point 108 to the right of the maximum torque operating point P.

Since the slip of the induction motor 10 is controlled to increase during low-speed operation in this way, the torque pulsation of the induction motor 10 moves away from the natural vibration frequency band of the forklift, and as a result, the hunting vibration of the forklift due to the torque pulsation is significantly reduced. .

In addition, when the slip frequency is increased in this way, the voltage command ■ is increased and the motor applied voltage is increased as described above, thereby compensating for the decrease in motor torque due to the increase in the slip frequency. As a result, light load slow speed operation of the induction motor 10 is possible despite an increase in the slip frequency.

In addition, when the motor load increases, it is possible to obtain sufficient motor torque for driving by increasing the voltage command V by further pressing the accelerator pedal.

As explained above, according to this embodiment, the induction motor 10
Since the slip frequency of the induction motor 10 is increased during light load slow speed operation, the induction motor 10 is operated at a higher shear frequency, which causes its torque pulsation to move away from the natural vibration frequency band of the forklift, and therefore its torque Forklift hunting vibration caused by pulsation is significantly reduced.

Further, according to this embodiment, since the voltage applied to the motor is increased along with the increase in the slip frequency, it is possible to maintain light load slow speed operation of the induction motor 10 regardless of an increase in the slip frequency.

(Effects of the Invention) As explained above, according to the present invention, the slip frequency and motor applied voltage are controlled to increase during light load slow speed operation of the induction motor. It is possible to reliably drive an electric vehicle while avoiding hunting vibrations caused by torque pulsation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a preferred embodiment of the apparatus according to the present invention, and FIG. 2 is a very torque characteristic diagram illustrating the operation of the embodiment shown in FIG. 10... Induction motor 12... Rotation speed detector 14... Slip frequency command generator 16... Modulation ratio calculator 18... Adder 20... Multiplier 24... Accelerator command generation Device 26...Sine wave generator 32...Inverter Patent applicant Nissan Motor Co., Ltd. Figure 2 Torque bus

Claims (1)

[Claims] (1) Accelerator command generation means for generating an accelerator command; motor rotation speed detection means for detecting the rotation speed of the induction motor; slip frequency command generation means for generating a slip frequency command according to the motor rotation speed; and a voltage command generating means for generating a voltage command according to the motor rotation speed; a slip frequency command increasing means for increasing a slip frequency command when the induction motor is running at a slow speed; and a voltage command increasing means for increasing the voltage command when the induction motor is running at a slow speed. A variable voltage variable frequency induction motor control device comprising: voltage command increasing means;