JPH0947082A - Pwm inverter having dead time correcting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize highly accurate speed and torque control by providing a dead time correction signal generator for receiving the output from a current detector and a set dead time correction value and delivering a dead time correction signal corresponding to the current value. SOLUTION: A dead time correction signal generator 42 receives a primary current I and a set dead time correction value K and delivers a dead time correction signal Vd'. An adder 62 adds a voltage command signal V* and the dead time correction signal Vd' to produce a corrected voltage command signal V**' which is outputted to a power converter 1. A dead time correction signal generator 42 performs dead time correction not dependent on the current detection accuracy and outputs the corrected voltage command signal V**' to a power converter 1 by adding a special dead time correction signal Vd' to the voltage command signal V*.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a P having a dead time correction function for improving the characteristics of torque and speed.
It relates to the WM inverter.

[0002]

2. Description of the Related Art Generally, a dead time is inserted in order to prevent a short circuit between power devices, but this is because the voltage applied to an induction motor (hereinafter simply referred to as "motor") fluctuates from a voltage command value and a current waveform. Distortion, torque,
It affects speed as ripples. Therefore, it is necessary to correct the dead time.

FIG. 3 shows a conventional example, in which 1 is a power converter, 2 is an electric motor, 3 is a current detector, 41 is a dead time correction signal generator, 5 is a control circuit, and 61 is an adder. In FIG. 3, the power converter 1 that drives the electric motor 2 supplies electric power to the electric motor 2 via the current detector 3. Current detector 3
Detects the primary current I of the electric motor 2 and outputs it to the dead time correction signal generator 41. Dead time correction signal generator
41 receives the primary current I and the dead time correction amount set value K as input, and as shown in FIG. 4, generates a step-like dead time correction signal Vd according to the current polarity. here,
FIG. 4 is a waveform diagram showing the relationship between the primary current I and the dead time correction signal Vd. That is, if (I> 0), (Vd
= K), (I = 0), (Vd = 0), and (I <0), (Vd = -K) dead time correction signal Vd is output to the adder 61.

The control circuit 5 outputs a voltage command signal V * for controlling the output torque of the electric motor 2 by the power converter 1.
Output to the adder 61. In the adder 61, the voltage command signal V *
And the dead time correction signal Vd are added, and the corrected voltage command signal V ** is output to the power converter 1.

[0005]

In the prior art of this kind, which uses means for judging the current polarity and giving a stepwise amount of dead time correction, the dead time correction depends on the accuracy of the current detector. It ended up being a thing. This is because when the current polarity changes, the current value is very small and it is difficult to detect the current accurately, and if the polarity is erroneously determined, an appropriate dead time correction amount cannot be given. That is, in the step-like correction, additional correction or insufficient correction occurs when the current polarity changes. Therefore, the characteristics of torque and speed are deteriorated especially at low speed and light load. Therefore, an object of the present invention is to provide a device having a simple structure capable of performing speed and torque control with higher accuracy than dead time correction that does not depend on current detection accuracy.

[0006]

The present invention has been made in view of the above points, and in particular, the dead time correction corresponding to the current value is made by inputting the current detector output and the dead time correction amount set value. It is configured by including a dead time correction signal generator for transmitting a signal.

By the means for solving such problems, the following actions can be achieved. That is, the dead time correction amount is given according to the state of the current value, and the smooth correction according to the state of the current value is performed near the change in the current polarity, so that the dead time correction that is not affected by the wrong polarity determination The voltage command signal can be modified by the amount, and good control characteristics can be realized in which the influence of dead time does not appear on the characteristics of speed and torque.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The dead time correction signal generator which outputs the dead time correction signal according to the current value by inputting the output of the current detector and the set value of the dead time correction amount according to the present invention is specifically ( K ≧ I ≦ −K),
A dead time correction signal that is smooth along the current waveform can be given to the adder that obtains the voltage command signal as one input as the other input. Hereinafter, the present invention will be described in more detail with reference to the drawings.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of an essential part of an embodiment of the present invention represented in a manner similar to FIG. 3, in which 42 is a dead time correction signal generator, 62 is an adder, and Vd 'is dead time correction. Signal, V
** 'is a correction voltage command signal. That is, the dead time correction signal generator 42 inputs the primary current I and the dead time correction amount setting value K and sends out the dead time correction signal Vd ′, and the adder 62 outputs the voltage command signal V * and the dead time correction signal Vd ′. Is added and the corrected voltage command signal V ** 'is output to the power converter 1.

Here, the dead time correction signal generator 42
Is, for example, as shown in FIG.
Depending on the current value of the primary current I, d ′ can be used as follows. (A) If (I> K), a signal is generated as a fixed amount of (Vd '= K), thereby eliminating the influence of dead time and improving the characteristics of speed and torque. (B) If (K ≧ I ≧ −K), then (Vd ′ = I) is set and smooth correction is performed along the current waveform. Also, instead of the current waveform, an n-th order curve may be approximated and corrected. As a result, the influence of dead time can be eliminated, dead time correction can be performed without depending on the detection accuracy of the current detector, and the characteristics of speed and torque can be improved. (C) If (I <-K), a signal is generated as a fixed amount of (Vd '=-K), thereby eliminating the influence of dead time and improving the characteristics of speed and torque.

In this way, the dead time correction signal generator 42 performs the dead time correction independent of the current detection accuracy, and further adds the special dead time correction signal Vd 'to the voltage command signal V *. The corrected voltage command signal V ** 'can be output to the power converter 1.
Exceptional

[0012]

As described above, according to the present invention, the dead time correction amount is smoothly changed in the vicinity of the change of the current polarity, so that the dead time correction independent of the current detection accuracy is realized to realize the speed and torque ripples. It is possible to provide a device having a simple structure capable of performing high-accuracy speed and torque control with reduced power consumption. And there.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a relationship between a primary current and a dead time correction signal for easy understanding of the dead time correction signal generator of FIG.

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a waveform diagram showing a relationship between a primary current and a dead time correction signal for facilitating understanding of the dead time correction signal generator of FIG.

[Explanation of symbols]

 1 power converter 2 induction motor (motor) 3 current detector 41 dead time correction signal generator 42 dead time correction signal generator 5 control circuit 61 adder 62 adder I primary current K dead time correction amount set value Vd dead time Correction signal Vd 'Dead time correction signal V * Voltage command signal V ** Modified voltage command signal V **' Modified voltage command signal

Claims (1)

[Claims] 1. A power converter that outputs a variable frequency variable voltage alternating current, an induction motor driven by the power converter, and a control that gives a voltage command signal for driving the induction motor to the power converter. A circuit, a current detector that detects the primary current of the induction motor, a dead time correction signal generator that outputs a dead time correction signal using the current detector output and a dead time correction amount set value as input, and the voltage command P having a dead time correction function, which is configured to include a signal and a dead time correction signal as an input and output a correction voltage command signal to the power converter.
In the WM inverter, the dead time correction signal generator receives the output of the current detector and the set value of the dead time correction amount and outputs a dead time correction signal according to the current value of the output of the current detector. A PWM inverter having a characteristic dead time correction function.