JPS6091889A - Controller of ac motor - Google Patents

Abstract

PURPOSE:To prevent the decrease in the effective voltage applied to a motor by controlling so that the amplitude of a triangular wave produced from a triangular wave generator becomes smaller than the amplitude of a current command value signal when the rotating speed is the prescribed value or higher. CONSTITUTION:When an AC motor 7 rotates at a high speed, the amplitude of a triangular wave Tr generated from a triangular wave generator 16 is reduced as compared with the final current command value i** to increase the ON time TON of the output pulse of a PWM circuit 14. Thus, the effective current applied to the motor 7 is increased to suppress the influence of the decrease in the voltage due to the loss due to the pulse width modulation and the counterelectromotive force generated in the motor 7, thereby improving the efficiency of the motor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an AC motor control device that controls a motor using pulse width modulation.

(Background of the Invention) Conventionally, a device for controlling an AC motor using pulse width modulation (hereinafter referred to as PWM) was disclosed in Japanese Patent Laid-Open No. 58-5
There is one as shown in Japanese Patent No. 7820.

FIG. 1 is a block diagram showing a schematic configuration of a device that controls an AC motor using such PWM. In the same figure a
3, based on the torque command value 8 from the torque command device 1, the microcomputer 2 sets a current command value (hereinafter referred to as current command value) to be applied to the AC motor 7 in order to realize the corresponding torque. (covering) i*.

The microcomputer 2 also feeds back rotational speed data ω of the AC motor 7 supplied from the counter 11. Note that the counter 11 counts pulse train signals from a tacho generator 10 provided on the output shaft of the AC motor 7.

The current regulator 3 uses the current command IIfii' and the current given to the AC motor 7 (hereinafter, the current actual wAI11[
) is detected by the current detector 8 and the current actual value i obtained is input, and the current command value is adjusted so that the actual current Wli matches and exceeds the current command value 18, and the final current command is obtained. The output 'TJ- is given as the value i*8.

The PWM circuit 4 pulse-width modulates the final current command value (hereinafter referred to as final current command value) 11* and supplies the resulting pulse signal P1 to the driver circuit 5.

The inverter 6 is driven by the driver circuit 5 and converts the power supply voltage supplied from the battery 9 into three-phase AC corresponding to the final current command value i** to drive the motor 7.
This is what supplies the world to.

Although omitted in the figure for simplicity, the above actual current value i, final current command value/'', output P of the PWM circuit 3,
The driver circuit 4 outputs three phases.

FIG. 2 is a diagram showing an example of the configuration of the PWM circuit 4. As shown in FIG.

As shown in the figure, the PWM circuit 4 is constituted by a comparator 41 and the like that performs level discrimination between the triangular wave Tr from the triangular wave generator 42 and the final current command value 8, and from the comparator 41, A pulse signal P is outputted by pulse width modulating the final current command value i** supplied as a sine wave.

Further, the triangular wave generator 42 is supplied with a constant voltage (2) from a constant voltage light generator 43, so that the amplitude of the triangular wave Tr output from the triangular wave generator 42 is kept constant.

The amplitude of this triangular wave Tr is such that when the AC motor 7 is operated at the rated rotational speed, the rated output is generated "ψ".
is set to

However, in the conventional AC motor control device described above, the amplitude of the triangular wave Tr generated from the triangular wave generator 42 in the PWM circuit 4 is constant, resulting in the following disadvantages.

That is, as shown in FIG. 3(a), when the AC motor 7 is rotating at a relatively low speed, the final current command I
Since the frequency of the triangular wave 7r is higher than the frequency of the triangular wave 7r, the voltage (effective voltage) applied to the AC motor 7 by the pulse width modulated output P by the PWM circuit 4 is equal to the power supply voltage of the battery 9. The maximum effective voltage (theoretical maximum effective voltage is 65% of the power supply voltage)
%).

On the other hand, when the rotational speed of the AC motor 7 becomes high, the frequency of the ffi final current command i** and the frequency of the triangular wave Tr become close to each other, as shown in FIG. 4 per cycle of the final current command value 188.
The proportion of the total ON time of the output P in 3 decreases,
This reduces the effective voltage.

Furthermore, when the AC motor 7 is rotating at high speed, the back electromotive voltage generated in the AC motor 7 is higher than when it is rotating at low speed, so the effective voltage is This will result in a further decline.

In this way, when the AC motor 7 is rotating at a relatively high speed, the output of the AC motor 7 is effectively activated in the configuration in which the amplitude of the triangular wave 7r in the PWM circuit 4 is constant as described above. This results in a decrease in efficiency.

(Object of the Invention) An object of the present invention is to enable efficient operation of a device that controls an AC motor using pulse width modulation even when the rotational speed of the AC motor is high. . - (Structure of the Invention) In order to achieve the above object, the present invention provides that when the rotational speed of the AC motor is equal to or higher than a predetermined rotational speed, the amplitude of the triangular wave generated from the triangular wave generator constituting the pulse width modulator is reduced. is controlled so that t is smaller than the amplitude of the current command value signal.
It is characterized by having the following structure.

(Description of Embodiment) Hereinafter, one embodiment of the present invention will be explained in detail using the drawings from FIG. 4 onwards. Incidentally, in this figure, the same components as those of the conventional example shown in FIG.

As shown in FIG. 4 (in this embodiment device, the first
The conventional 1-lux command device 1 shown in the figure is constructed using an accelerator sensor 12 that detects the stroke m (handle, referred to as accelerator stroke amount) of the accelerator pedal, and the control device shown in the figure An example is shown in which the following is applied as a running control device for an electric vehicle.In the device of this embodiment, the PWM circuit 14 is as follows.
In addition to a triangular wave generator 16 and a comparator 17 that performs level discrimination between the triangular wave 1-r generated from the triangular wave generator 16 and the final current command value i*11 supplied from the current regulator 3, the triangular wave generator 16 is provided with an amplitude adjuster 15 for adjusting the amplitude of the triangular wave r.

The amplitude adjuster 15 is constituted by a microcomputer circuit mainly composed of a microprocessor, for example, and converts the accelerator stroke value supplied from the accelerator sensor 12 into an A/D converter. /D21 inverter, an interface circuit for inputting the motor rotational speed data ω from the counter 11, a D/A converter for supplying the output data as an analog voltage signal vS to the triangular wave generator, and other memories. It is something.

A data table storing triangular wave amplitude data S determined two-dimensionally based on the correlation between the accelerator stroke MA and the motor rotational speed ω is stored in the memory.

As shown in Fig. 5, the structure of the data in the above data table is as follows: the area where the motor rotation speed is high and the accelerator stroke is large (indicated by I in the figure), and the other area (indicated by I).
It is classified into two areas (indicated by 1 in the figure).

Then, when the data in area I above is read out,
The voltage of the voltage signal VS applied to the triangular wave generator 16 is
It is supplied to the triangular wave generator 16 as a reference voltage set in advance based on the rated output of the AC motor, and thereby,
As shown in FIG. 6(a), the amplitude of the triangular wave Tr output from the triangular wave generator 16 is set to an amplitude value that is larger than the amplitude of the final current command value i'' output from the current regulator 3. It is set to be S1.

In addition, on the platform where the data of the above 11 areas was read,
The voltage value of the voltage signal S supplied to the triangular wave generator 16 becomes below the M quasi-voltage value, and as a result, as shown in FIG.
As shown in a), the amplitude of the triangular wave 7r is set to be an amplitude S2 that is sufficiently small compared to the amplitude of the final current command IITti''''.

With the above configuration, when the electric vehicle starts running fj Ittl, the motor rotational speed ω is low and the accelerator stroke ff1A is large if there is a sudden start, and small in other cases. Under these circumstances, Since the motor rotational speed ω is low, the data read from the data table in FIG. 5 is the data in the area I.

In addition, when driving at a constant speed on a highway, etc., the motor rotation speed ω is high, but the accelerator thrust is 0.
- Since ff1A is small, even under such a situation, the data read from the data table in FIG.
It will be read from the area (2).

Therefore, in these cases, as shown in FIG. 6(a), the amplitude of the triangular wave T-r in the PWM cycle vB14 is equal to the reference amplitude S, which is set based on the rated output of the AC motor 7.
+, and the AC motor 7 is configured to operate efficiently.

On the other hand, for example, when driving on a highway, if the driver depresses the accelerator pedal greatly in order to overtake or overtake, the motor rotation speed ω will be high and the accelerator stroke ff1A will also be large. The data read from the above data table is shown in Figure 5.
The data in the area will be read out.

As a result, as shown in FIG. 7(a), the amplitude of the triangular wave Tr generated from the triangular wave generator 16 becomes a sufficiently small amplitude S2 compared to the final current command value 1lI11, and is output from the comparator 17. The pulse signal P is a pulse signal with a long ON time TON as shown in FIG. 2(b).

FIG. 6(b) is a diagram showing the waveform of the pulse signal P that would be generated if the amplitude of the triangular wave Tr was set as the reference amplitude S1. ) shows the ON/OFF time per pulse of the pulse signal P, and the ON time of the pulse signal [) shown in FIG. 7(b) 1-
It can be seen that the signal is shorter than that of ON.

Therefore, when the AC motor 7 is rotating at a high speed as in the device of this embodiment, the PW
Assuming that the ON time TON of the output pulse of the M circuit 14 is human,
By increasing the effective voltage applied to the AC motor 7, it is possible to suppress the effects of loss due to pulse width modulation and voltage drop due to the back electromotive force ratio generated in the AC motor 7, and improve the efficiency of the AC motor. can.

Therefore, when rapidly accelerating in a high-speed driving state, such as when applied to an electric vehicle, it is possible to increase the output of the AC motor compared to the conventional one, and improve acceleration response.

Although the above embodiments have been explained using an example of application to an electric vehicle, the present invention can also be applied to any other control + wave device for performing 1.1 speed changes of an AC motor. Needless to say, it is.

Further, the configuration of the amplitude adjuster includes, for example, a comparator that determines the motor rotation speed and the size of the accelerator stroke stone, and a voltage switching circuit that switches the voltage applied to the triangular wave generator in response to the output J of the comparator. C is also good.

(Effects of the Invention) As explained above in detail, the AC motor control device according to the present invention prevents a drop in the effective voltage applied to the motor even when the AC motor rotates at high speed, and can be operated efficiently.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of a conventional AC motor 1Ilj control device, Figure 2 is a block diagram showing the configuration of a conventional PWM circuit, and Figure 3 is the final current when the motor rotates at low speed and at high speed. FIG. 4 is a block diagram showing the configuration of an embodiment of the AC motor control device according to the present invention, and FIG. 5 is a diagram showing the waveform of the command value and the triangular wave. The structure of the data table configured in the memory is not shown, and the table map shown in Figs. 6, 13 and 7 shows the main output waveforms of the I) WM circuit of the same device when the motor is rotating at low speed and when the motor is rotating at high speed. FIG. 2... Current command value generator 3... Current regulator 5... Driver circuit 6... Inverter 7... AC motor 8... Current detector 9... Battery 10... Tacho Generator 14...PWM circuit 15...Amplitude adjuster 16...Triangular wave generator 17...Comparator Patent applicant Nissan Motor Co., Ltd.)! \t-

Claims (1)

[Claims] (1) In an AC motor control device that pulses a current command value signal applied to the AC motor using a pulse width modulator, and drives a power converter based on the pulse signal to control the current applied to the AC motor; A rotation speed detector for detecting the rotation speed of the AC motor is provided, and the pulse width modulator includes a triangular wave generator; a comparator that compares the current command value signal and the triangular wave and outputs a pulse signal; and an amplitude controller that variably controls the amplitude of the triangular wave to be smaller than the amplitude of the current command value signal when the rotational speed of the AC motor is equal to or higher than a predetermined rotational speed. Covering AC motor control device.