JPH05176594A - Inverter device for induction motor - Google Patents

Abstract

PURPOSE:To provide an inverter device for an induction motor capable of obtaining output voltage having a waveform close to a desired waveform without being affected by a dead time. CONSTITUTION:A potential detector 10 detects the fluctuation of potential at the node of switching elements Q1, Q2 while using potential at the node of resistors R1, R2 having the same value connected between both ends of the series circuit of a pair of the switching elements Q1, Q2 constituting an inverter section as a reference. A dead time detector 11 detects a dead time from an output from a signal forming circuit 20. A sample-and-hold circuit 12 inputs an output from the potential detector 10 to an integrating circuit 13 during the input of the dead-time detecting signal of the dead time detector 11. The integrating circuit 13 inputs an integrated output to a compensator 16 through a buffer 14 and a filter circuit 15. The compensator 16 corrects the amplitude of a control signal Vu consisting of sine waves generated from a control signal generator 23 in response to the integrated output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for an induction motor.

[0002]

2. Description of the Related Art FIG. 2 shows a plurality of switching elements Q _{1 to} Q _{6 each having a} flyhole diode D connected in antiparallel.
1 shows a basic circuit configuration of an inverter device for an induction motor having an inverter part formed by connecting bridges. In the illustrated inverter device, for example, a three-phase AC power supply AC is rectified by a diode bridge DB, and
Smoothing is performed by the smoothing capacitor C ₀ , and the rectified and smoothed output is converted into a three-phase alternating current by the inverter unit and supplied to the induction motor M. The inverter portion has six respective two switching elements Q ₁ to Q ₆ are connected in series, a so-called flip-bridge configuration the series circuit each connected in parallel.

These switching elements Q₁~ Q₆Is a triangle
Wave as a carrier signal, and this carrier signal and control signal
Is input to the PWM circuits 1U, 1V, 1W
Pulse width modulation is performed to obtain PWM signals that are shifted by 120 degrees,
From this PWM signal, the signal forming circuits 2U, 2V, 2W
Switching element Q for each phase U, V, W pair₁, Q₂,
…, Q_Five, Q₆Drive signals Up, which have opposite phases for alternately driving
Un, ..., Wp, Wn were created. Pair here
Switching element Q₁, Q₂, ..., Q_Five, Q₆At the same time
Switch pair to prevent a short-circuit condition.
Element Q₁, Q ₂, ..., Q_Five, Q₆Are both off
To the signal forming circuits 2U, 2V, 2W so as to provide a section
Using the on-delay circuit, drive signals Up, Un,
..., Wp and Wn were created.

Considering, for example, the U phase, the signal forming circuit 2U delays the PWM signal from the PWM circuit 1U corresponding to the U phase shown in FIG. The signal shown in FIG. 3 (b) that rises and falls in accordance with the fall of the PWM signal is generated to obtain the drive signal Up, and the rise of the PWM signal is delayed by a time t to rise. A signal shown in FIG. 3 (c) which is made to fall in accordance with the rising of the signal is created to obtain a drive signal Un having a phase opposite to that of the drive signal Up, and the switching element Q ₁ is driven by these drive signals Up and Un. , Q ₂ are alternately turned on and off to generate a U-phase output. Here, the time t is a dead time when both the switching elements Q ₁ and Q ₂ are turned off.

[0005]

By the way, in FIG. 2, when the direction of the output current flowing through the point a is positive (direction A)
The electric potential at point a is as shown in FIG. In this case, since the current flows through the fly-hole diode D ₁ during the dead time t, the potential at point A is on the negative side. On the other hand, when the direction of the output current flowing at the point a is negative (direction B), the potential at the point a becomes as shown in FIG.
In this case, during the dead time t, the flyhole diode D
_Since the current flows through ₂ , the potential at point a becomes the positive side.

Therefore, there is a problem that the output voltage waveform becomes a waveform of B different from the desired sine waveform A as shown in FIG. 3 (f) under the influence of the dead time t. The present invention has been made in view of the above problems, and an object thereof is to provide an inverter device for an induction motor that can obtain an output waveform close to a desired waveform without being affected by dead time. It is in.

[0007]

In order to achieve the above object, the present invention provides an inverter section formed by bridge-connecting switching elements in which flyhole diodes are respectively connected in antiparallel, and an output voltage of the inverter section. Creates a PWM signal formed so as to be a sine wave, and creates drive signals of mutually opposite phases from this PWM signal, and the pair of switching elements of each phase have a predetermined phase angle deviation by this drive signal. In the inverter device for an induction motor, which consists of a control unit that alternately turns on and off and applies an output voltage to the induction motor connected between the connection points of each pair of switching elements, the intermediate potential of the pair of switching elements is used as a reference. Is a potential detection circuit that detects the potential at the connection point of the pair of switching elements and a switch that turns off the pair of switching elements. A dead time detection circuit for detecting time and a compensating means for integrating the output of the potential detection circuit during dead time detection by the dead time detection circuit and compensating the section voltage of the PWM signal according to the integrated output. A time compensation circuit is provided for each phase.

[0008]

According to the present invention, therefore, the section voltage of the PWM signal can be corrected in accordance with the potential of the connection point of the pair of switching elements of the inverter section during the dead time, and as a result, the dead time. It is possible to obtain an output voltage waveform of the inverter unit that is hardly affected by

[0009]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 shows an embodiment implemented in a three-phase U, V, W inverter device, and in FIG. 1, only the U phase is shown for the sake of simplicity. In this embodiment, the switching elements Q ₁ to the potential of the pair of resistors R _1, R ₂ at the connection point of the same value connected across the series circuit of the switching elements Q _1, Q ₂ constituting the inverter section based on , A potential detection circuit 10 for detecting a variation in the potential at the connection point of Q ₂ , a buffer 17 for amplifying the detection signal of the potential detection circuit 10, and a dead time t for detecting a dead time t from the output of the signal forming circuit 20 of the control section. A time detection circuit 11, a sample and hold circuit 12 whose operation mode is switched by a dead time detection signal corresponding to the period of the dead time t output from the dead time detection circuit 11, and an output of the sample and hold circuit 12. An integrating circuit 13 for integrating,
A buffer 14 that amplifies the output of the integration circuit 13, a filter circuit 15 that removes a signal component that could not be integrated by the integration circuit 13, and a compensator 16 that corrects the control signal Vu on the control unit side by the output of the filter circuit 15. It has a dead time compensation circuit. The potential detection circuit 10
The variable resistance VR of is for adjusting the detection output level.

On the other hand, the control unit controls the frequency setting signal F from the outside.
Based on the above, a calculator 21 for outputting a frequency command f, a V / F calculator 22 for performing a V / F calculation by the frequency command f from the calculator 21 and outputting a voltage command V, and the frequency command f , A control signal generator 23 for generating a control signal Vu consisting of a sine wave of a predetermined frequency having a predetermined amplitude according to the voltage command V, a triangular wave generation circuit 24 for outputting a triangular wave which is a carrier signal, and the compensator 16 for outputting. A comparator 25 that compares the control signal Vu ′ with the triangular wave from the triangular wave generating circuit 24 to create a pulse width-modulated PWM signal that is the basis of a drive signal that turns on and off the switching elements Q ₁ and Q ₂ . drive signal for driving the PWM signal alternately switching elements Q _1, Q ₂ as described above Up, the signal forming circuit 20 composed of on-delay circuit for generating a Un, this Et drive signals Up, comprised of the driver circuit 26 for driving the switching elements Q _1, Q ₂ by Un.

Thus, in this embodiment, the NAND circuit of the drive signals Up and Un from the signal forming circuit 20 is taken by the NAND circuit 11a of the dead time detecting circuit 11 and then integrated to integrate it, so that the dead time period t The dead time detection signal slightly delayed corresponding to the sample and hold circuit 12
Is output to. The sample-and-hold circuit 12 inputs the detection signal of the potential detection circuit 10 to the integration circuit 13 via the buffer 17 while the dead time detection signal is input. That is, during the dead time t, the positive pulsed output voltage during the period when the diode D ₁ is on and the negative pulsed output voltage during the period when the diode D ₂ is on are input to the integrating circuit 13 and integrated. The integrated output thus obtained is input to the compensator 16 as a correction signal Cu via the buffer 14 and the filter circuit 15.

The compensator 16 is a control signal generator 23 of the control unit.
The control signal Vu from the control signal Vu by adding the correction signal Cu
The amplitude of u is adjusted, and the corrected control signal Vu ′ is output. This control signal Vu 'becomes a control signal in which the influence of the dead time t is corrected, and this control signal Vu'
The comparator 25 creates a PWM signal in which the dead time t has been corrected based on and the triangular wave which is the carrier signal.
In this PWM signal, the voltage in a minute section dividing the time axis is corrected by the control signal Vu ′, and the switching elements Q ₁ and Q ₂ are driven on / off by the drive signals Up and Un created by the corrected PWM signal. Then,
It is possible to generate the output voltage U having a waveform that is hardly affected by the dead time t.

Therefore, the switching elements Q ₁ and Q are generated by the drive signals Up and Un created by the corrected PWM signal.
By driving ₂ on / off, it is possible to generate an output voltage U having a waveform that is hardly affected by the dead time t. By the way, in the above embodiment, the triangular wave generating circuit 2
4 and the control signal generator 23, the PWM signal is created by comparing the triangular wave generated by the control signal generator 23 and the control signal Vu. The triangular wave having a predetermined carrier frequency and the sine wave having a predetermined frequency having a predetermined amplitude are generated. May be obtained by calculation and assumed, and a software processing method of creating a predetermined PWM signal by performing a comparison calculation based on the assumed result may be used. In this case, if the correction value is given from the compensator 16, A process of correcting the calculation assumption of the control signal Vu based on the calculation result to obtain a corrected PWM signal is performed.

[0014]

According to the present invention, in the induction motor inverter device configured as described above, a potential detection circuit for detecting the potential at the connection point of the pair of switching elements with reference to the intermediate potential of the pair of switching elements, The dead time detection circuit that detects the dead time when the pair of switching elements are both turned off, and the output of the potential detection circuit is integrated during the dead time detection of the dead time detection circuit, and the section voltage of the PWM signal is calculated according to this integrated output. Since the dead time compensating circuit including the compensating means for compensating is provided for each phase, the section voltage of the PWM signal corresponds to the potential of the connection point of the pair of switching elements of the inverter unit, corresponding to the dead time period. It is possible to correct, and as a result, it is possible to generate an output voltage having a waveform that is hardly affected by the dead time from the inverter unit. Achieve the cormorant effect.

[Brief description of drawings]

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

FIG. 2 is a basic circuit configuration diagram of an inverter device for an induction motor.

FIG. 3 is a waveform diagram for explaining the operation of a conventional example.

[Explanation of symbols]

10 Potential Detection Circuit 11 Dead Time Detection Circuit 12 Sample-and-Hold Circuit 13 Integration Circuit 14 Buffer 15 Filter Circuit 16 Compensator 20 Signal Forming Circuit 23 Control Signal Generator Q ₁ , Q ₂ Switching Element R ₁ , R ₂ Resistance

Claims (1)

[Claims] 1. An inverter section formed by bridge-connecting switching elements in which fly-hole diodes are respectively connected in anti-parallel, and a PWM signal formed so that an output voltage of the inverter section becomes a sine wave. At the same time, drive signals having mutually opposite phases are created from this PWM signal, and the switching elements of each phase are alternately turned on and off with a predetermined phase angle shift by this drive signal, and the switching elements of each pair are connected. In an inverter device for an induction motor, which comprises a control unit that applies an output voltage to an induction motor connected between points, a potential that detects the potential at the connection point of the pair of switching elements with reference to the intermediate potential of the pair of switching elements. The detection circuit, the dead time detection circuit that detects the dead time when the pair of switching elements are both turned off, and the dead time A dead time compensating circuit for integrating each output of the potential detecting circuit during the dead time detection of the system detecting circuit and compensating means for compensating the section voltage of the PWM signal according to the integrated output. An inverter device for an induction motor, characterized by: