JP2003274673A - Inverter apparatus and dead time compensation method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set an appropriate amount of dead time compensation to prevent erroneous compensation. <P>SOLUTION: A control unit 17 compares a current value detected by U- and V-phase current detectors 13 and 14 with a preset threshold. When the current value becomes a set threshold or less based on the switching speed of transistors Q1 to Q6, the control unit 17 reduces the amount of dead time compensation based on the detected current value. When the current value becomes a set threshold or less based on the detection accuracy of an output current, the control unit 17 increases a reduction rate in the amount of dead time compensation. Additionally, when the detected current value becomes so small to the extent that whether it is positive or negative cannot be discriminated, the amount of dead time compensation is set to 0. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device and its dead time compensation method.

[0002]

2. Description of the Related Art An inverter device is a device for converting an applied DC link voltage into an AC voltage, and is used especially for driving an induction motor.

FIG. 5 shows the configuration of a conventional voltage type (VVVF) inverter device. Inverter device voltage converter 5
1 includes switches S1 to S4. In order to convert the applied DC link voltage into an AC voltage, first the switch S
After turning off S2 and S3, the switches S1 and S4 are turned on. When the switches S1 and S4 are turned off and the switches S2 and S3 are turned on at the next timing, an AC voltage is generated,
An alternating current as shown in FIG. 6 flows through the load 52.

In the voltage type inverter, the switches S1 and S
2, or in order to prevent vertical short circuit in the current path between the switches S3 and S4, as shown in FIG.
Is provided. In order to ensure this dead time under any condition, it is necessary to perform dead time compensation.

For the dead time compensation, a method of detecting the output voltage of the inverter device and compensating for the dead time of the voltage command signal based on the detected output voltage, and a method of detecting the output current of the inverter device and measuring the output current There is a method of compensating for the dead time of the voltage command signal based on the sign.

Comparing these two methods, the former method requires a new voltage detector. On the other hand, according to the latter method, the current detector provided in the inverter device can be used. Therefore,
Considering cost and space saving, the latter method is preferably used.

[0007]

However, in the latter dead time compensation method, if the output current becomes small, it becomes difficult to determine whether the output current is positive or negative, and there is a risk of incorrect compensation. If incorrect compensation is performed and the output frequency of the inverter device is 50 Hz, the voltage drop will be small even if incorrect compensation is performed.
In particular, when the pulse width becomes narrow at about 1 to 5 Hz, the current waveform is distorted, which causes a voltage drop.

The present invention has been made in view of such conventional problems, and an object thereof is to provide an inverter device capable of preventing erroneous compensation by a simple method and a dead time compensation method thereof. To do.

[0009]

In order to achieve this object, an inverter device according to a first aspect of the present invention comprises switching elements connected in series and to which a DC voltage is applied. A switching element is provided for preventing a short circuit due to simultaneous turn-on of the voltage conversion section that converts the DC voltage into an AC voltage by turning on and off based on a control signal, and the switching elements connected in series. A control unit that sets a dead time compensation amount for compensating the dead time based on the current value of the output current of the voltage conversion unit and supplies a control signal with the dead time compensation to the voltage conversion unit. It is a thing.

The control unit compares the current value of the output current of the voltage conversion unit with a threshold value preset based on the switching speed of the switching element, and determines whether the current value of the output current is less than or equal to the threshold value. And a compensation amount reduction unit that reduces the dead time compensation amount based on the current value of the output current when the determination unit determines that the current value of the output current is less than or equal to a threshold value. You may do it.

The determination means compares the current value of the output current of the voltage conversion unit with a threshold value preset according to the detection accuracy of the current value, and determines whether the current value of the output current is less than or equal to the threshold value. If the determination means determines that the current value of the output current is less than or equal to a threshold value set according to the detection accuracy, the compensation amount reducing means determines the dead time based on the current value of the output current. It may be configured to increase the reduction rate for reducing the amount.

A method of compensating for dead time of an inverter device according to a second aspect of the present invention comprises a switching element connected in series, to which a DC voltage is applied, and the switching element is turned on based on a control signal. , In an inverter device including a voltage conversion unit that converts the DC voltage into an AC voltage by turning it off, the dead time provided for preventing a short circuit due to simultaneous turning on of the switching elements connected in series is set to the voltage. The method further comprises: a step of setting based on a current value of an output current of the conversion section; and a step of supplying the dead-time-compensated control signal to the voltage conversion section.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an inverter device according to an embodiment of the present invention will be described with reference to the drawings. The configuration of the inverter device according to the present embodiment is shown in FIG. The inverter device according to the present embodiment is a voltage type inverter in which the output voltage is a square wave, and the DC smoothing capacitor 11
A voltage converter 12, a U-phase current detector 13, a V-phase current detector 14, a rotor position detector 15, a DC link voltage detector 16, and a controller 17. ing.

The DC smoothing capacitor 11 includes a DC power source 18
This is for smoothing the DC voltage of.

The voltage conversion unit 12 includes a DC smoothing capacitor 1
1 converts the smoothed DC link voltage into an AC voltage based on the voltage command value supplied from the control unit 17, and includes transistors Q1 to Q6 and diodes D1 to D1.
6 and 6 are provided.

The transistors Q1 to Q6 are switching elements that switch based on the pulse signal supplied from the control unit 17, and the transistors Q1 to Q6 are provided with, for example, an IGBT (Injection Enhanced Gate Transistor).
sistor) is used.

The collectors of the transistors Q1, Q3 and Q5 are connected to the positive electrode of the DC smoothing capacitor 11.
The collectors of the transistors Q2, Q4, Q6 are connected to the emitters of the transistors Q1, Q3, Q5, respectively.
The emitters are connected to the negative electrode of the DC smoothing capacitor 11, respectively.

At the connection point between the emitter of the transistor Q1 and the collector of the transistor Q2, an induction motor (in the figure,
Write as "IM". ) 19 U-phase windings are connected, and a V-phase winding is connected to the connection point between the emitter of the transistor Q3 and the collector of the transistor Q4.
A W-phase winding is connected to a connection point between the emitter of the and the collector of the transistor Q6. And the transistor Q1
The voltage command signals as control signals are supplied to the gates of the transistors Q1 to Q6 to turn them on and off.

The diodes D1 to D6 are transistors Q
It is a diode for diverting the output current when 1 to Q6 are turned off. The cathodes of the diodes D1 to D6 are connected to the collectors of the transistors Q1 to Q6, respectively, and the anodes thereof are respectively connected to the transistor Q1.
Are connected to the emitters of Q6. Voltage converter 12
Applies the converted AC voltage to the three-phase induction motor 19.

U-phase current detector 13 and V-phase current detector 14
Are the current values iu and iw of the output currents supplied to the U-phase and W-phase primary windings (stator windings) of the induction motor 19, respectively.
Respectively detected.

The rotor position detector 15 includes an induction motor 19
The rotation angle of the rotor shaft with respect to the stator winding shaft (for example, the U-phase winding shaft is used as a reference shaft) is detected.

The DC link voltage detector 16 detects the voltage value Vdc of the DC voltage smoothed by the DC smoothing capacitor 11.

The control unit 17 acquires current values iu and iv from the U-phase current detector 13 and the V-phase current detector 14, respectively, and the voltage conversion unit 12 based on the acquired current values iu and iv.
To control. In the present embodiment, vector control is used as the control method, and the control unit 17 generates the voltage command signals Tst (u), Tst (v), Tst (w) as pulse signals and converts the voltage. Output to the unit 12.

Further, the control unit 17 obtains the dead time compensation amount Tdcom corresponding to the current value of the detected current, and based on the dead time compensation amount Tdcom, the voltage command signals Tst (u), Tst (v),
Dead time compensation of Tst (w) is performed. In order to perform such dead time compensation, the threshold value Iref is added to the current value of the detected current.
(A), Iref (B), and Iref (C) are provided.

The threshold value Iref (A) is a current value set on the basis of the detection accuracy of the output current.
It is set to about 0%. The threshold Iref (B) is a threshold set based on the switching speed of the transistors Q1 to Q6, and is set to, for example, about 20% of the rated current. Iref (C) is a threshold value for determining whether or not the compensation amount for dead time compensation is set to 0, and is set to, for example, about 5% of the rated current.

The control unit 17 has a memory, and the threshold values Iref (A), Iref (B), and Iref (C) are stored in this memory in advance. Further, constants and the like necessary for calculation of dead time compensation are also stored in this memory.

Next, the operation of the inverter device according to the present embodiment will be described. The DC smoothing capacitor 11 smoothes the DC voltage of the DC power supply 18. The DC link voltage smoothed by the DC smoothing capacitor 11 is applied to the transistors Q1 to Q6 of the voltage conversion unit 12. The DC link voltage detector 16 determines the voltage value Vdc of this DC link voltage.
To detect.

An alternating voltage is generated by turning on and off the transistors Q1 to Q6, and a current flows through each winding of the induction motor 19 in the U, V and W phases. The U-phase current detector 13 and the V-phase current detector 14 have current values iu and iv of the currents flowing through the U- and V-phase windings of the induction motor 19, respectively.
To detect.

The control unit 17 generates the voltage command signals Tst (u), Tst (v) and Tst (w) based on the vector control.

This operation will be described with reference to the flowchart of FIG. The controller 17 acquires the current values iu and iv from the U-phase current detector 13 and the V-phase current detector 14, respectively (step S11). The current value of the W-phase current iw is calculated from the current value iu and the V-phase current value iv based on the condition of three-phase equilibrium.

The controller 17 acquires the rotor position from the rotor position detector 15 (step S12). Control unit 17
Is the current value i in the stationary coordinate system with the stator axis as the observation coordinate.
Coordinate conversion of u, iv, and iw is performed using the rotor position into a rotating coordinate system having the rotor axis as the observation coordinate, and the exciting current value id and the torque current value iq are obtained (step S13).

The controller 17 controls the current command value id * of the exciting current.
And the current command value iq * of the torque current are acquired (step S14).

The control unit 17 controls the current command value id * of the exciting current.
And the exciting current value id, and the deviation eq between the torque current value iq * and the torque current value iq are calculated, and PI (proportional integral) calculation of the calculated deviations ed and eq is performed. Voltage command values vd *, v such that the deviations ed, eq are zero respectively
Find q * (step S15).

The control unit 17 controls the obtained voltage command values vd *, vd.
From q *, three-phase voltage command values vu *, vv *, vw * in the stationary coordinate system are obtained based on the rotor position (step S16).
The control unit 17 controls the voltage command signals Tst (u) and Ts as pulse signals based on the obtained three-phase voltage command values vu *, vv *, vw *.
t (v) and Tst (w) are generated (step S17).

The controller 17 controls the generated voltage command signal Tst.
Dead time compensation of (u), Tst (v), and Tst (w) is performed (step S18).

This dead time compensation will be described with reference to FIG. In the section IV where Iref (B) <Im, the current value Im can be accurately detected, and the dead time compensation amount Tdcom is set to a constant value (kded).

In the section III of Iref (A) <Im ≦ Iref (B),
If the dead time compensation amount is constant at kded, the current value Im
As becomes smaller, the dead time compensation becomes excessive. Therefore, in this section III, the dead time compensation amount Tdcom is reduced according to the current value Im.

Dead time compensation amount Tdco in this section III
m is calculated based on the following equation (1).

[Equation 1] ... (1)

In the section II of Iref (C) <Im ≦ Iref (A),
Since the current value Im is further reduced and the voltage drop is also reduced, if the dead time compensation amount Tdcom is set based on the equation (1), overcompensation may occur and distortion may occur in the output voltage and the output current of the inverter device. is there. Therefore, the section
In II, the reduction rate of the dead time compensation amount Tdcom is further increased as the current value Im becomes smaller.

Dead time compensation amount Tdcom in this section II
Is calculated based on the following equation (2).

[Equation 2] ... (2)

In the section I of 0 <Im ≦ Iref (C), it is difficult to determine the positive / negative of the current due to the detection accuracy of the U-phase current detector 13, the V-phase current detector 14, etc., and if Tdcom> 0, it becomes erroneous. Compensation is caused and distortion occurs in the output voltage and output current of the inverter device. Therefore, the dead time compensation amount Tdcom is set to 0 in this section I.

The control unit 17 sets the dead time compensation amount Tdcom in this way and performs dead time compensation. This operation will be described based on the flowchart of FIG. Since the dead time compensation operation is common to the U phase, V phase, and W phase, the dead time compensation for only the U phase will be described here.

The control section 17 acquires the detected current value Im (step S21). The current value Im is the current value of the output current of the inverter device detected by the U-phase current detector 13 and the V-phase current detector 14.

The control unit 17 controls the current value Im and each threshold value Iref.
(A), Iref (B), and Iref (C) are compared (step S2
2).

The control unit 17 determines that the current value Im is the threshold value Iref (C).
It is then determined whether or not (0 <Im ≦ Iref (C)) (step S23).

When it is determined that the current value Im is less than or equal to the threshold value Iref (C) (Yes in step S23), the control unit 17 sets the dead time compensation amount Tdcom to 0 (step S24).

The control unit 17 adds 0 as the dead time compensation amount Tdcom to the pulse width tst of the voltage command signal Tst (step S25).

Next, when it is determined that the current value Im exceeds the threshold value Iref (C) (No in step S23),
The control unit 17 determines that the current value Im is equal to or less than the threshold value Iref (A) (Im ≦ I
ref (A)) is determined (step S26).

When it is determined that the current value Im is less than or equal to the threshold value Iref (A) (Yes in step S26), the control unit 17 determines the dead time compensation amount Tdcom based on the equation (2).
Is calculated (step S27).

The control unit 17 controls the dead time compensation amount Tdcom.
When calculated, the sign of the current value Im is determined (step S28).

When the sign Tsgn of the current value Im is positive (Yes in step S28), the upper arm (transistor Q)
1, Q3, Q5) for dead time compensation of the voltage command signal Tst, the control unit 17 subtracts the dead time compensation amount Tdcom calculated based on the equation (2) from the pulse width tst of the voltage command signal Tst ( Step S29).

When the sign Tsgn of the current value Im is negative (No in step S28), the lower arm (transistor Q)
2, Q4, Q6) is dead time compensation of the voltage command signal Tst, the control unit 17 adds the dead time compensation amount Tdcom calculated based on the equation (2) to the pulse width tst of the voltage command signal Tst ( Step S30).

Next, when it is determined that the current value Im exceeds the threshold value Iref (A) (No in step S26),
The control unit 17 determines whether or not the current value Im is equal to or less than the threshold value Iref (B) (step S31).

When it is determined that the current value Im is less than or equal to the threshold value Iref (B) (Yes in step S31), the controller 17
Calculates the dead time compensation amount Tdcom based on the equation (1) (step S32).

Then, when the sign Tsgn of the current value Im is positive, the controller 17 calculates the dead time compensation amount T calculated based on the equation (1) from the pulse width tst of the voltage command signal Tst.
When dcom is subtracted and the sign Tsgn is negative, the voltage command signal Ts
The dead time compensation amount Tdcom calculated based on equation (1) is added to the pulse width tst of t (steps S28 to S28).
30).

Next, when it is determined that the current value Im exceeds the threshold value Iref (B) (No in step S31),
The control unit 17 sets a constant value kde for the dead time compensation amount Tdcom.
d1 is set (step S33).

When the sign Tsgn of the current value Im is positive, the controller 17 subtracts this dead time compensation amount Tdcom from the pulse width tst of the voltage command signal Tst, and the sign Tsg.
If n is negative, the dead time compensation amount Tdcom is added to the pulse width tst of the voltage command signal Tst (step S2).
8 to S30).

The controller 17 controls the voltage command signals Tst (u), Tst (v), Tst for which the dead time compensation has been performed in this way.
(w) is output to the bases of the transistors Q1 to Q6 of the voltage conversion unit 12.

As described above, according to the present embodiment, the dead time compensation amount is set based on the current value of the output current. Therefore, the dead time compensation amount is optimized by a simple calculation according to the output current of the inverter device. Dead time compensation can be performed.

Therefore, the output frequency of the inverter device is 1
Even if the pulse width becomes narrower at about 5 Hz,
The current waveform can be prevented from being distorted, and the voltage can be maintained. Then, this can improve the driving performance particularly when the induction motor 19 is driven at a low frequency, and can realize the downsizing and cost reduction of the inverter device.

Various modes are conceivable for carrying out the present invention, and the present invention is not limited to the above-described modes. For example, the thresholds Iref (A), Iref (B), Iref (C) are
The values are not limited to those in this embodiment, and may be set as appropriate according to noise, switching speed of switching elements and the like, detection accuracy of the U-phase current detector 13, the V-phase current detector 14, and the like. You can

Further, the transistor Q1 of the voltage conversion unit 12
A bipolar transistor, a FET (field effect transistor), a thyristor or the like can be used for Q6 depending on the power capacity.

The induction motor 19 is not limited to the three-phase type, but may be the two-phase type or the multi-phase type having more than three phases. Further, it is possible to use a synchronous motor instead of the induction motor. Further, the speed control of the induction motor is not limited to vector control, and primary frequency control, voltage / frequency control, or the like can be used.

[0064]

As described above, according to the present invention,
False compensation can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inverter device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a vector control operation of a control unit in FIG.

FIG. 3 is an explanatory diagram showing the operation of the inverter device.

FIG. 4 is a flowchart showing dead time compensation performed by the control unit of FIG.

FIG. 5 is an explanatory diagram showing the principle of a conventional inverter device.

6 is an operation waveform diagram of the inverter device of FIG.

FIG. 7 is an enlarged view of the waveform of FIG.

[Explanation of symbols]

12 Voltage converter 13 U-phase current detector 14 V phase current detector 16 DC link voltage detector 17 Control unit 19 induction motor

Claims (4)

[Claims] 1. A direct current voltage is converted into an alternating voltage by comprising switching elements connected in series to which a direct current voltage is applied, each of the switching elements being turned on and off based on a control signal. And a dead time compensation amount for compensating a dead time provided for preventing a short circuit due to simultaneous turn-on of the voltage conversion unit and the switching elements connected in series to the current value of the output current of the voltage conversion unit. An inverter device, comprising: a control unit which is set based on the above and supplies a control signal which has been subjected to dead time compensation to the voltage conversion unit. 2. The control unit compares the current value of the output current of the voltage conversion unit with a threshold value preset based on the switching speed of the switching element, and determines whether the current value of the output current is less than or equal to the threshold value. When the determination unit determines whether the current value of the output current is less than or equal to a threshold value, a determination unit that determines whether or not the dead time compensation amount is a compensation amount reduction unit that reduces the dead time compensation amount based on the current value of the output current. The inverter device according to claim 1, further comprising: 3. The determination means compares the current value of the output current of the voltage converter with a threshold value preset according to the detection accuracy of the current value, and determines whether the current value of the output current is less than or equal to the threshold value. The compensation amount reducing means determines whether or not the current value of the output current is less than or equal to a threshold value set according to the detection accuracy, and the dead amount based on the current value of the output current. The inverter device according to claim 2, wherein the inverter device is configured to increase a reduction rate for reducing the time compensation amount. 4. A voltage for converting a direct current voltage into an alternating current voltage by including a switching element connected in series to which a direct current voltage is applied, the switching element being turned on and off based on a control signal. In an inverter device including a conversion unit, a step of setting a dead time provided for preventing a short circuit due to simultaneous turning on of the switching elements connected in series, based on a current value of an output current of the voltage conversion unit, And a step of supplying the dead-time-compensated control signal to the voltage converter, the dead-time compensation method for an inverter device.