JPH06189559A - Method for compensating dead-time in inverter control - Google Patents

Abstract

PURPOSE:To reduce a torque ripple in a low-frequency range without enlarging a CPU process. CONSTITUTION:An output voltage command signal is generated at a step S1. A decrement in output voltage is produced at a step S2, and the command signal is superimposed with the decrement in the same polarity to generate a synthetic signal at a step S3. At a step S4, this signal is supplied as an output voltage command signal to a next step S5. A PWM pulse width information table is formed at the step S5. The data is read from the information table at a step S6 to obtain a drive signal for an inverter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dead time compensating method in inverter control for suppressing the influence of a short circuit prevention period on the output side in a PWM inverter control device.

[0002]

2. Description of the Related Art A PWM inverter is often used to drive an AC motor at a variable speed. In this case, when trying to drive the motor without the speed feedback loop, hunting of the current is likely to occur in the specific frequency region at the time of light load, which may cause uncontrollability, and large torque ripple. I have a big problem.

In particular, at low speed driving, the effect of torque ripple becomes large, and the effective variable speed range becomes a rotation speed range of about 20: 1, which is not applicable to applications where vibration at low speeds is disliked.

The cause of this is that the power switching elements T _{U to} T _Z forming the inverter main circuit 41 shown in FIG. 4 are turned on.
If there is a delay in the ON / OFF operation and the switching elements Tu to Tz connected in series for each phase u, v, and w are turned on at the same time for a short time, a DC power supply short circuit is caused and the switching elements Tu to Tz are destroyed. . Therefore, it is necessary to delay the switching command for turning the OFF state of each of the switching elements Tu to Tz into the ON state. This OF
The delay time of the command from the F state to the ON state is called dead time, and this influence causes waveform distortion in the output voltage as shown in FIG. In FIG. 4, 42 is a motor.

The voltage reduction amount ΔV of the waveform distortion due to the dead time when the PWM method is the triangular comparison method is ΔV = Ed * Td * Fc where Ed: inverter main circuit DC voltage (V) Td: dead time ( S) Fc: Can be represented by triangular wave frequency (Hz).

In the recent PMW inverter, from the viewpoint of noise reduction, the triangular wave frequency Fc is set in the audible range (about 10 KHz).
The number set higher is increasing, and this increase in switching frequency also makes the problem of waveform distortion a big problem.

As a method for solving this problem, Japanese Patent Application No. 3-
No. 225449 discloses an inverter control for compensating the waveform distortion of the dead time by superimposing the output voltage decrease caused by the dead time on the output voltage command signal with the same polarity as the command signal, and using the composite signal as the output voltage command. ,
This is a compensation method that determines the polarity of this sine wave at the stage of synthesizing the three-phase sine wave output voltage signals from the two-phase sine wave output voltages and synthesizes the necessary compensation component with this sine wave.

[0008]

Problems to be Solved by the Invention Japanese Patent Application No. 3-2 mentioned above.
In No. 25449, as a reason for adopting the dead time compensating method, there is a limitation in the computing capacity when performing control using a general-purpose CPU. However, with the recent improvement in the capability of the CPU, it has become possible to perform PWM waveform shaping, which is an output voltage command of the inverter, inside the CPU.

The PWM waveform is created by a method of generating an equivalent voltage of the pulse width of the PWM signal in a sine wave shape. Conventionally, as shown in FIG. 6, by comparing a sine wave with a triangular wave or a sawtooth wave, It was generated by hardware. The pulse width information thus generated is prepared in advance as a table in the memory of the ROM or RAM, and the read position is changed from this table at a speed proportional to the output frequency. Based on this, by changing the L / H level of each output phase, it is intended to equivalently obtain a sinusoidal PWM waveform as shown in FIG.

Normally, the pulse width information table is written with data for making the output waveform a sine wave,
A method is used in which the PWM waveform is equivalently a sine wave. However, the PWM waveform is equivalently a sine wave,
When the main circuit inverse conversion element is driven by this sine wave, the problem of waveform distortion due to the presence of dead time occurs, as described above, and particularly affects the torque ripple in the low speed region.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a dead time compensating method in inverter control which can reduce torque ripple in a low frequency region.

[0012]

In order to achieve the above-mentioned object, the first aspect of the present invention superimposes an output voltage decrease signal due to dead time on the output voltage command signal in the same polarity as the command signal. In the inverter control for compensating the waveform distortion of the dead time by using the combined signal as the output voltage command, the sine wave PWM using the combined signal as the output voltage command
A pulse width information table is created, and the data read from this table is used as a drive signal for the inverse conversion element.

A second aspect of the present invention is characterized in that a plurality of sine wave PWM pulse width information tables are prepared in advance and the tables are switched and used according to the output frequency of the inverter.

[0014]

Since the PWM pulse width information table is created and the data read from this table is used, the dead time can be compensated with certainty without increasing the CPU processing, and the torque ripple in the low frequency region is reduced. it can.

Since a plurality of PWM pulse width information tables are prepared and used by switching the tables according to the output frequency, it is possible to use only in the low frequency region where torque ripple becomes a problem.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, S ₁ is a step of sending an output voltage command signal, and the command signal sent from this step S ₁ has the same polarity as that of the output voltage decrease due to the dead time from step S ₂ in step S ₃ . It is superimposed and synthesized. The combined signal is used as an output voltage command signal in step S ₄ to create a pulse width information table in step S ₅ . From the table created in step S ₅ reads the data provided as the drive signal of the inverse conversion device that data in step S _6.

Although the method of creating the table changes depending on the output resolution of the sine wave, the switching frequency and the maximum output frequency, the output waveform is a value sampled at regular intervals.

FIG. 2 is a block diagram when the inverter is controlled by the output of the CPU. In this FIG.
In the table created in step S ₅ shown in the above, the table 21 is a memory including a ROM or a RAM. The data read from this memory 21 is stored in the CPU 2
Processed in 2. The processed data is given from the CPU 22 to the inverse conversion driver 23 as an output voltage command signal. The output of the inverse conversion driver 23 is supplied to the inverse conversion elements 24a and 24b of the inverter 24, and the operation of the inverter 24 is performed.

By creating the pulse width information table using the composite signal as the output voltage command signal as described above, dead time compensation is possible, CPU processing is not increased, and torque ripple in the low frequency region is reduced. Can be reduced. The dead time compensation waveform at this time is shown in FIG.

By preparing a plurality of the above-mentioned tables in advance and switching and changing the pulse width information table to be referred to according to the output frequency, dead time compensation can be performed only in a low speed region where torque ripple becomes a problem.

[0021]

As described above, according to the present invention,
The dead time can be compensated without increasing the CPU processing, and the torque ripple in the low frequency region can be reduced. Further, since the control stability in the low frequency region is high, the rotation unevenness has conventionally occurred in the rotation speed range of about 1/20, but a smooth rotation can be obtained even in the rotation speed range of about 1/200. You can Furthermore, since a plurality of pulse width information tables can be prepared and the pulse width information table to be referenced can be switched and used according to the output frequency, dead time compensation is used only in the low frequency region where torque ripple becomes a problem. It is possible.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention.

FIG. 2 is a block diagram when an inverter is controlled by a CPU.

FIG. 3 is a waveform diagram at the time of dead time compensation obtained in the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a configuration driven by an inverter.

FIG. 5 is an output voltage waveform diagram.

FIG. 6 is a time chart of a three-phase waveform for one cycle.

FIG. 7 is a sine waveform diagram.

[Explanation of symbols]

 21 ... Memory table 22 ... CPU 23 ... Reverse conversion drive 24 ... Inverter

Claims (2)

[Claims] 1. An inverter control for compensating for waveform distortion of dead time by superimposing an output voltage decrease caused by dead time on an output voltage command signal with the same polarity as the command signal and using this composite signal as an output voltage command. 2. A dead time compensating method in inverter control, characterized in that a sine wave PWM pulse width information table using the combined signal as an output voltage command is created, and the data read from this table is used as a drive signal for an inverse conversion element. 2. The dead time compensation in inverter control according to claim 1, wherein a plurality of sine wave PWM pulse width information tables are prepared in advance, and the tables are switched and used according to the output frequency of the inverter. Method.