JP3206866B2 - Inverter dead time compensation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for compensating a command voltage according to the polarity of a current detected by detecting a current flowing through a coil of an induction motor.

[0002]

2. Description of the Related Art Generally, in a method of compensating for a dead time of an inverter, a coil current of an induction motor is detected, and the current is determined as one of a positive current, a zero current, and a negative current, and a command voltage is corrected. is there.

[0003]

In the above conventional method,
Since the zero-current detection width is constant, when the inverter has a high capacity and the induction motor has a small capacity, there is a problem that the primary current is entirely within the zero-current detection width and dead time cannot be compensated. In addition, in the circuit for detecting the zero current, a capacitor using a capacitor and a resistor is used to prevent noise.
It was detected through the R filter circuit. For this reason, the detected current is a harmonic and is detected later than the actual current. Therefore, there is a problem that wrong dead time compensation is performed.

Further, if the wiring connecting the inverter and the induction motor becomes long, the current flowing through the inverter is disturbed due to leakage current or the like, so that there is a problem that dead time cannot be compensated. The present invention has been made in view of the above problems,
An object of the present invention is to provide a method for compensating a dead time of an inverter, which can reliably perform a dead time compensation.

[0005]

To achieve the above object, according to the first aspect of the present invention, a command proportional to a set frequency is provided.
AC voltage calculation that generates an AC voltage reference based on voltage
According to the voltage reference from the AC voltage calculator.
An inverter that performs M control and drives an induction motor;
The polarity of the current flowing through the coil of the conductive motive is detected, and the current
The above command voltage with the AC voltage calculator with the correction voltage according to the polarity
The voltage base output by the AC voltage calculator
When correcting the standard, a certain value width was set around zero
When the detection current exists in the zero current detection width for a predetermined time, the zero current
It was detected as a flow, in the dead time compensation method for performing the correction using the zero current, the inverter and the induction motor
The feature is that the zero current detection width is adjusted by the wiring length to connect the motor, and when the inverter has a high capacity and the induction motor has a small capacity, the primary current is dead without entering all the zero current detection current width. Time compensation , especially with inverter
The length of the wiring connecting the induction motor
Also happening is disturbed Ru can dead-time compensation.

[0006]

[0007] According to the second aspect of the present invention, in proportion to the set frequency,
AC voltage that generates an AC voltage reference based on the command voltage
Voltage calculator and the voltage reference from this AC voltage calculator.
Inverter that performs PWM control and drives an induction motor
And the polarity of the current flowing through the induction motor coil,
The above voltage is calculated by the AC voltage calculator with the correction voltage according to the polarity of the current.
Output from the AC voltage calculator by correcting the voltage
When compensating the voltage reference, it has a predetermined value range centered on zero.
If the detected current exists in the added zero current detection width for a predetermined time,
Is detected as a zero current, and the supplementation is performed using the zero current.
In the dead time compensation method that performs positive
Connection between the inverter and the induction motor.
The zero current detection width can be adjusted by adjusting
The primary current is zero current detection current
Dead time compensation without entering the flow width
In particular, by adjusting the set frequency, the detection current
Even if the current is detected later than the actual current,
System compensation and connect inverter and induction motor
Dead even if current disturbance occurs due to long wiring
Time compensation is Ru can.

According to a third aspect of the present invention, in the first and second aspects of the present invention, an upper limit value and a lower limit value are provided for the zero current detection width. By increasing the value, the primary current is prevented from completely entering the zero current detection width. By setting the lower limit, the zero current detection width does not become zero, so that dead time compensation can be performed.

According to a fourth aspect of the present invention, in the first and second aspects of the present invention, a length of a wiring connecting the inverter and the induction motor is detected by a change in current, and a zero current detection width is adjusted based on the detected length. In the invention of claim 5 , the claim
In the inventions according to the first and second aspects, a wiring length for connecting the inverter and the induction motor is set, and a zero-current detection width is adjusted based on the wiring length. The wiring is lengthened by adjusting the zero-current detection width. Dead time compensation can be performed even when the current waveform is disturbed.

According to the invention of claim 6 , in claims 1, 2, 4,
The invention according to claim 5 , characterized in that the value of the correction voltage is adjusted based on the length of the wiring connecting the inverter and the induction motor,
By setting or detecting the wiring length, dead time compensation can be performed by adjusting the value of the correction voltage.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. First, the dead time compensation of the inverter will be described. The output voltage of the inverter is controlled according to the voltage command. However, the output voltage causes a control error with respect to the voltage command value for the reason described later. As a result, the rotational speed and torque control characteristics of the induction motor are degraded.

For example, as shown in FIG. 5, a general inverter used in an induction motor driving device is a multi-phase transistor in which flywheel (regeneration) diodes D _{1 to} D ₆ are connected in anti-parallel. Switching element Q ₁
To Q ₆ and the main circuit 1 constituted by bridge-connecting, are constituted by a PWM control circuit (not shown) for controlling the ignition of the switching elements Q ₁ to Q ₆ of the main circuit 1. Note that a voltage obtained by converting three-phase alternating current into direct current by the rectifier circuit 3 and the smoothing capacitor 4 is applied to the main circuit 1 as a power supply.

In the PWM control circuit, a voltage command signal having a PWM waveform is created by comparing the control voltage signal a and the triangular wave b shown in FIG. 6C, and the switching element Q of the main circuit 1 is generated in accordance with the voltage command signal. controls ignition of ₁ to Q _6, controls the output voltage of the inverter 1. In the main circuit 1,
When a switching element (for example, Q ₁ and Q ₂ ) connected in series to the power supply (both ends of the smoothing capacitor 4) commutates, when a period occurs in which both switching elements are simultaneously in the firing state,
During that period, the power supply is short-circuited. Therefore, in order to prevent this power supply short circuit, one switching element (for example, Q ₁ ) is turned off and the other switching element (for example, Q ₂ ) is turned on. This ignition delay time is a so-called inverter dead time.

This point will be further described with reference to FIG. Now, when the current i flows in the direction of the arrow in FIG. 5, the PWM obtained by comparing the control voltage signal a with the triangular wave b
When the transistors Q ₁ and Q ₂ are alternately turned on and off in accordance with the waveform, the connection point x between the switching element Q ₁ and the switching element Q ₂ changes from a negative potential to a positive potential because of switching. dead time T _D of the element Q ₁
Only late. Conversely, when the current i flows in the direction opposite to the arrow in FIG. 1, the connection point x is until the change to the positive potential or negative potential, delayed dead time T _D of the switching element Q _2. As a result, with respect to a desired waveform indicated by a thick solid line in FIG.
Or lost by _D, and or added partially, Figure 6
The waveform shown in FIG. This is shown in FIG.
Is equivalent to a pulse-like voltage having a width of the dead time T _D shown in FIG. Therefore, the output voltage of the inverter is reduced by the pulse voltage.

The pulse voltage has a relationship with the polarity of the current i whose phase is advanced by an angle φ from the rotating magnetic flux shown in FIG. This angle φ is the d-axis current (excitation current) shown in FIG.
And an angle φ formed by the current and the q-axis current (torque current). Here, when the current i is positive, the pulse voltage is negative, and when the current i is negative, the pulse voltage is positive. This pulse voltage can be approximated to a square wave voltage, and its amplitude ΔV is ΔV = Ed × t
d × fc (Ed is pulse voltage, td is pulse width, fc
Is the frequency). Therefore, by adding an approximated square wave voltage (correction voltage) according to the polarity of the current i, when the current i is detected to be zero, a square wave voltage having a polarity opposite to the polarity that has been corrected so far. (Correction voltage).
However, in the correction at the time of the zero current, when the current i is detected as zero, a square wave voltage (correction voltage) opposite to the polarity corrected so far is added. In this manner, compensation is performed to prevent a decrease in output voltage due to the dead time of the inverter.

Next, zero current detection and dead time compensation which are the basics of the present invention will be described. First, when a current starts to flow , the current is detected by a current detector to determine the polarity of the current, and the polarity of the correction voltage is determined using the polarity. In consideration of the influence of noise on the current detected in step (1), a zero current detection width is provided as shown in FIG. 8 to provide hysteresis. FIG.
(B) is an enlarged view in a frame (a) of FIG. Now
It is assumed that the detection current flows from the positive polarity to the negative polarity as shown in FIG. If the detected current has been within the zero current detection time continuously for a certain period of time after entering the zero current detection width, it is detected as a zero current. That this is time zero current detection time and hump. Next, if the detected current is continuously on the negative polarity side outside the zero current detection width for a certain time,
Detects negative current. This certain time is referred to as a positive / negative current detection time. After the negative current is detected,
Unless the detected current is zero within the current detection width for a certain period of time, it is detected as a negative current. This time is called a positive / negative current holding time. Here, when noise is included in the detected current, zero current and positive / negative current are detected by a method as shown in FIG. In other words, if the detection current once enters the zero current detection width and noise enters outside the zero current detection width before the zero current detection time elapses, the zero current is newly added from the point of the noise. Re-measure the detection time. Also, when noise within the zero current detection width enters the positive / negative current detection time, the positive / negative current detection time is newly measured. In this case, it is desirable to detect the zero current more quickly and extend the positive / negative current holding time. As one of the methods, FIG.
As described above, the noise is ignored in the zero current detection time and the positive / negative current holding time, and the time is re-measured in the positive / negative current detection time.

In the above description, the case where the detection current flows from the positive polarity to the negative polarity has been described. However, the same processing is performed when the detection current flows from the negative polarity to the positive polarity. Thus, when the current is positive, the positive correction voltage is used. When the current is negative, the negative correction voltage is used. When the current is zero, the negative correction voltage is used when the current changes from the positive current to the zero current. By applying a positive correction voltage when the current is reached, dead time compensation can be performed as shown in FIG. In FIG. 12A, a thin line A indicates an uncorrected command voltage, a thick line B indicates a corrected command voltage, and ΔV indicates a corrected voltage. FIG. 12B shows the primary current. This is the correction by the current.

Next, an embodiment of the present invention will be described based on a specific configuration shown in FIG. The configuration of this embodiment includes a V / F converter 5 that converts and outputs a command voltage V that is proportional to a set frequency, a phase angle calculator 12 that integrates the set frequency to obtain a phase angle θ of the voltage, Voltage references Vu ^* , Vv ^* ,
An AC voltage calculator 13 that outputs Vw ^* , and a voltage reference Vu.
^{Based on *} , Vv ^* , Vw ^* , PWM control is performed, and an inverter 1 composed of a switching element such as a transistor for driving an induction motor 2 and a three-phase current iu, iv, i
and a primary current that is output to a zero current detection width calculator 11 described later as a primary current peak value from the three-phase currents iu, iv and iw output from the detector 6 as a primary current peak value. A peak value calculator 7 and a wire length detector 8 for detecting the wire length of the inverter 1 and the induction motor 2 from the three-phase current
And a storage unit 9 for storing the wiring length detected by the wiring length detector 8 or a wiring length set from the outside, a setting frequency ωr ^* being set and stored, and a phase angle with the V / F converter 5. Set frequency ωr ^* to arithmetic unit 12 and zero current detection width arithmetic unit 11
And a zero current detection width calculator 11 that calculates a zero current detection width from the set frequency ωr ^{*, the} primary current peak value and the wiring length, and outputs the calculated zero current detection width to the AC voltage calculator 13. .

The zero current detection width is calculated by the zero current detection width calculator 11 as follows. In other words, the zero current detection width calculator 11 is, as shown in FIG.
Value of the primary current output from the
From the set frequency ωr ^* output from 0, the wiring length output from the storage device 9, the preset reference frequency, the reference wiring length, and the upper and lower limit values, it is obtained based on the equation (1).
A in FIG. 2 shows a calculated value by the equation (1).

[0020]

(Equation 1)

(1) The dead time compensation described above is performed using the zero current detection width. When dead time compensation is performed without considering the wiring length, the primary current becomes as shown in FIG. 3A when the wiring length is short, and as shown in FIG. 3B when the wiring length is short. . Therefore, a method for detecting the wiring length is shown in FIG.
As shown in (a), a voltage based on the command voltage without dead time compensation is applied to the induction motor 2, and the time from when the command voltage becomes zero to when the primary current becomes zero is detected by the wire length detector 8. The time is multiplied by a constant (FIG. 4B shows the primary current when the wiring length is short, and FIG. 4C shows the primary current when the wiring length is long. This is the time of the portion A shown in these figures).

Also, depending on the wiring length, the dead time can be compensated well by adding the correction voltage obtained from the equation (wire length-reference wiring length) / reference wiring length × correction voltage, even if the wiring length becomes long.

[0023]

According to the first aspect of the present invention, the zero current detection width is adjusted.
Is adjusted by the wiring connecting the inverter and the induction motor
Therefore, even if current disturbance occurs due to wiring length, dead time
There is an effect that compensation can be performed.

According to a second aspect of the present invention , the peak value of the primary current
And set frequency, connect inverter and induction motor
Adjusting the zero current detection width by adjusting the wiring length and
The detected current is a harmonic and is detected later than the actual current
However, in addition to dead time compensation,
The length of the wiring connecting the induction motor
Also happening is disturbed Ru can dead-time compensation.

[0025]

According to a third aspect of the present invention, in the first and second aspects of the present invention, an upper limit value and a lower limit value are provided for the zero current detection width.
By providing the upper limit value, the set frequency becomes larger than the reference frequency, thereby preventing the primary current from being entirely within the zero current detection width.By providing the lower limit value, the zero current detection width does not become zero. There is an effect that dead time compensation can be performed.

According to a fourth aspect of the present invention, in the first and second aspects of the present invention, the length of a wiring connecting the inverter and the induction motor is detected by a change in current, and the zero current detection width is adjusted based on the detected length. According to a fifth aspect of the present invention, in the first and second aspects of the present invention, the wiring length for connecting the inverter and the induction motor is set, and the zero current detection width is adjusted based on the wiring length. There is an effect that dead time can be compensated even when the current waveform is disturbed due to the lengthening.

According to a sixth aspect of the present invention, in the first and second aspects of the present invention, the value of the correction voltage is adjusted based on the length of the wiring connecting the inverter and the induction motor. Therefore, the correction is performed by setting or detecting the wiring length. There is an effect that dead time compensation can be performed by adjusting the voltage value.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a zero current detection width according to the first embodiment.

FIG. 3 is an explanatory diagram of a primary current due to a difference in wiring length in the embodiment.

FIG. 4 is an explanatory diagram of a method for detecting a wiring length according to the embodiment;

FIG. 5 is a circuit diagram of a main circuit of the inverter.

FIG. 6 is an operation explanatory view of the above.

FIG. 7 is an explanatory diagram when a current is separated into an excitation current and a torque current.

FIG. 8 is an explanatory diagram of a method for detecting a zero current.

FIG. 9 is an explanatory diagram of a specific method of detecting zero current.

FIG. 10 is an explanatory diagram of a specific method of detecting zero current.

FIG. 11 is an explanatory diagram of a specific method of detecting zero current.

FIG. 12 is an explanatory diagram of a relationship between a primary current and a correction voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter 2 Induction motor 5 V / F converter 6 Detector 7 Primary current peak value calculator 8 Wire length detector 9 Storage device 10 Frequency setting device 11 Zero current detection width calculator 12 Phase angle calculator 13 AC voltage calculator

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-176593 (JP, A) JP-A-5-184157 (JP, A) JP-A-7-99793 (JP, A) JP-A-6-99793 32580 (JP, A) JP-A-9-47064 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/537 H02P 5/41 302

Claims (6)

(57) [Claims] (1) Based on a command voltage proportional to a set frequency.
An AC voltage calculator for generating an AC voltage reference;
PWM control is performed according to the voltage reference from the voltage calculator,
Inverter that drives the induction motor and coil of the induction motor
The polarity of the current flowing through the
Correcting the above command voltage with an AC voltage calculator with positive voltage
To correct the voltage reference output by the AC voltage calculator
At this time, the zero current detection width with a predetermined value width centered on zero
When the detected current is present for a predetermined time, it is detected as zero current.
In the dead time compensation method of performing the above-mentioned correction using the zero current , the inverter and the induction motor are connected.
A dead time compensation method for an inverter , wherein a zero current detection width is adjusted by a wiring length . 2. Based on a command voltage proportional to a set frequency.
An AC voltage calculator for generating an AC voltage reference;
PWM control is performed according to the voltage reference from the voltage calculator,
Inverter that drives the induction motor and coil of the induction motor
The polarity of the current flowing through the
Correcting the above command voltage with an AC voltage calculator with positive voltage
To correct the voltage reference output by the AC voltage calculator
At this time, the zero current detection width with a predetermined value width centered on zero
When the detected current is present for a predetermined time, it is detected as zero current.
Dead time to use the zero current to make the above correction
In the compensation method, the peak value of the primary current and the set frequency
And the wiring length for connecting the inverter and the induction motor
Adjusting the zero current detection width by adjusting
Inverter dead time compensation method of that. 3. The inverter dead time compensation method according to claim 1 , wherein an upper limit value and a lower limit value are provided for the zero current detection width . 4. A wiring length for connecting an inverter and an induction motor.
The dead time compensation method for an inverter according to claim 1 or 2, wherein a zero current detection width is adjusted based on the detected current change . 5. A wiring length for connecting an inverter and an induction motor.
The dead time compensation method for an inverter according to claim 1 or 2, wherein the zero current detection width is adjusted based on the above equation. 6. A wiring length for connecting an inverter and an induction motor.
More, claims, characterized in that to adjust the value of the correction voltage
Inverter dead time compensation method according to 1, 2, 4, or 5 .