JPH05260755A - Method and device for controlling invertor - Google Patents

Abstract

PURPOSE:To make it possible to suppress an adverse effect caused by a dead time, by computing a compensation amount on the basis of the amplitude and direction of an output current of an invertor and the amplitude of a stray capacitance of a switching element. CONSTITUTION:The operation of a controller for a phase U is explained in the following. A current detector 5 for the phase U detects the amplitude and direction of an output current 1 for the phase U and inputs them to a compensation amount computing part 1b. A sine wave voltage instruction generating part 1a generates a sine wave voltage instruction signal on the basis of a frequency instruction signal and an amplitude instruction signal and outputs it to an addition part 1c. The compensation amount computing part 1b computes a compensation amount in view of a stray capacity C and outputs it to the addition part 1c. A comparing part 1f compares the data from the addition part 1c with a triangular wave carrier signal from a triangular wave generating part 1e and generates a PWM signal. A delay generating part 1h inserts a dead time period (DT) into the PWM signal and drives a switching transistor(Tr) Q1. Besides, it inserts the DT into an inverted PWM signal from an inverting part 1g and drives TrO2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control method and an inverter control device. In particular, it is useful for controlling an AC electric motor for maintaining the pressure of the injection molding machine.

[0002]

2. Description of the Related Art An inverter is composed of a bridge circuit composed of switching elements, and is supplied to the switching elements so that a pair of upper and lower switching elements forming one side of the bridge circuit do not turn on at the same time. The control signal is provided with a dead time period (a period in which a pair of upper and lower switching elements are simultaneously turned off). This dead time period distorts the output voltage waveform of the inverter.

When the AC motor is driven by the inverter, the distortion of the output voltage waveform of the inverter causes pulsation of the torque of the AC motor and uneven rotation. In particular,
When the AC motor is operated at a low voltage and at a low speed, the influence is great and becomes a problem. For example, there is a problem in controlling the AC electric motor for maintaining the pressure of the injection molding machine (the rotation speed of the AC electric motor for maintaining the pressure of the injection molding machine must be 1 rpm or less, and the torque ripple must be 1% or less. ).

As a conventional inverter control technique for compensating for torque pulsation and uneven rotation of an AC motor, for example, Japanese Patent Publication No. 59-8152 and Japanese Patent Laid-Open No. 59-123 are available.
There are proposals disclosed in Japanese Patent Laid-Open No. 478 and Japanese Patent Laid-Open No. 62-239897.

FIG. 5 shows a sine wave inverter disclosed in Japanese Patent Publication No. 59-8152. This sine wave inverter 5
1 is to detect the output current direction for each phase, calculate a compensation amount according to the output current direction and the input command signal, and feed back the compensation amount to the switching time of the switching element.

FIG. 6 shows a control device for a voltage type inverter disclosed in Japanese Patent Laid-Open No. 59-123478. This voltage inverter control device detects the output current direction for each phase, calculates the compensation amount according to the output current direction and the size of the dead time period, and feeds back the compensation amount to the inverter voltage command. To do.

FIG. 7 shows a control method of the voltage source inverter disclosed in Japanese Patent Laid-Open No. 62-239897. This voltage source inverter control method detects the magnitude and direction of the output current for each phase, calculates the compensation amount according to the magnitude and direction of the output current, the motor winding resistance, and the wiring resistance,
The compensation amount is fed back to the inverter voltage command.

[0008]

In recent years, the switching frequency of switching elements has become higher and higher, and the influence of stray capacitances of the switching elements and wirings has increased accordingly. This will be described with reference to FIG. FIG. 4A shows a voltage command that is the basis of a signal that drives the switching element. FIG. 4B is an actual voltage waveform of the output of the inverter when the output current of the inverter flows from the inverter to the AC motor (this direction is positive). FIG. 4C shows when the output current of the inverter flows from the AC motor to the inverter (this direction is negative).
2 is an actual voltage waveform of the output of the inverter.

In FIG. 4B, at time t which is delayed by the dead time period DT from the rise of the PWM signal at time t0.
At 1, the upper switching element is turned on, and almost instantaneously rises from A to B. Although the upper switching element is turned off at the fall of the PWM signal at time t2, it takes time τ due to the stray capacitance of the switching element and the like, and C
To B '. Although there is actually a rise time from A to D, it is ignored here because it is smaller than the time τ.

In FIG. 4C, the lower switching element is turned off at the rising edge of the PWM signal at time t0, but it takes time τ due to the stray capacitance of the switching element and the like.
To D '. Time t which is delayed by the dead time period DT from the fall of the PWM signal at time t2
The switching element on the lower side is turned on at 3, and the state is lowered from C to B almost instantaneously. Although there is actually a fall time from C to B, it is ignored here because it is smaller than the time τ.

As described above, since the actual voltage waveform is broken due to the stray capacitance, the output voltage becomes excessive or insufficient. However, the conventional Japanese Patent Publication No. 59-8152, Japanese Patent Publication No. 59-123478, and Japanese Patent Publication No. 62-62. The technique disclosed in Japanese Patent No. 239897 does not consider the influence of the stray capacitance and has a problem that the stray capacitance is not compensated.

Therefore, an object of the present invention is to provide an inverter control method and an inverter control device for performing compensation in consideration of stray capacitance.

[0013]

The present invention detects the magnitude and direction of the output current of an inverter, and based on the magnitude and direction of the output current and the magnitude of stray capacitance of a switching element that constitutes the inverter, a compensation amount. Is provided and the output voltage of the inverter is compensated according to the compensation amount.

Further, according to the present invention, the output current detecting means (5-7) for detecting the magnitude and direction of the output current of the inverter (IV), and the output detected by the output current detecting means (5-7). The magnitude and direction of the current and the inverter (I
V), the compensation amount calculation means (1b to 3b) for calculating the compensation amount based on the size of the stray capacitance (C) of the switching elements (Q1 to Q6), and the compensation amount to the switching elements (Q1 to Q1). Provided is an inverter control device (100), comprising: a compensating means (1 to 3) for feeding back the switching time of Q6).

[0015]

In the inverter control method and the inverter control device of the present invention, the magnitude and direction of the output current of the inverter are detected, and the compensation amount is calculated based on the magnitude and direction of the output current and the magnitude of the stray capacitance of the switching element. (The calculation example of this compensation amount will be described in detail in the embodiment). Then, the output voltage of the inverter is compensated according to the compensation amount. In this way, since the stray capacitance is taken into consideration for compensation, it is possible to preferably suppress the adverse effect due to the dead time even when the switching element is switched to a higher frequency.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 is a configuration diagram of an inverter control device 100 according to an embodiment of the present invention. This inverter control device 100
Is a U-phase controller 1 and a V-phase controller 2
And a W-phase controller 3, a drive circuit 4, a U-phase current detector 5, a V-phase current detector 6, and a W-phase current detector 7, and controlling an inverter IV. Controls the rotation of the induction motor IM.

The U-phase controller 1 includes a sine wave voltage command generator 1a, a compensation amount calculator 1b, an adder 1c, a triangular wave generator 1e, a comparator 1f, an inverter 1g, and a delay generator. It is composed of 1h. The configurations of the V-phase controller 2 and the W-phase controller 3 are the same as those of the U-phase controller 1.

The U-phase current detector 5 has a U-phase output current I.
Is detected and input to the compensation amount calculation unit 1b of the U-phase controller 1. The same applies to the V-phase current detector 6 and the W-phase current detector 7.

The inverter IV is composed of a transistor bridge TB composed of switching transistors Q1 to Q6 such as IGBTs, and a diode bridge DB composed of flywheel diodes D1 to D6 connected in parallel to the switching transistors Q1 to Q6. ing. Further, the stray capacitance C exists in parallel with the switching transistors Q1 to Q6.

Next, the operation will be described. The sine wave voltage command generation unit 1a of the U-phase controller 1 generates a sine wave voltage command signal based on the frequency command signal and the amplitude command signal supplied from the outside, and outputs the sine wave voltage command signal to the addition unit 1c.

The compensation amount calculator 1b calculates the compensation amount and outputs it to the adder 1c. The calculation of this compensation amount is performed by the procedure shown in FIG. In step S1, the time τ of FIG. 4 is calculated from the time constant of the stray capacitance C and the load (VDC / | I |).
To calculate. That is, τ = C * (VDC / | I |). Here, as the stray capacitance C, for example, the drive capacitance of the switching transistors Q1 to Q6 is used. Also,
The load (VDC / | I |) is the inverter DC voltage VDC
Is divided by the magnitude | I | of the output current I.

In step S2, it is determined whether or not the time τ is longer than the dead time period DT, and if it is longer, step S3.
If not, go to step S4.

In step S3, the magnitude of the compensation amount VSE
Calculate T. That is, VSET = VDT * DT / (2 * τ) The meaning of this equation will be described with reference to FIG. FIG. 3A shows
It is a voltage command. FIG. 3B shows an actual voltage waveform of the output when the output current I flows from the inverter IV to the AC motor IM (I> 0), and the time τ is the dead time period D.
This is the case when it is larger than T. When the time τ is not taken into consideration, the average dead time compensation amount VDT is VDT = fc * VDC * DT. This is the area α of AA'DD 'in FIG.
(= VDC * DT) is multiplied by the carrier frequency fc and averaged. Next, considering time τ, the area β of CC′E in FIG. 3B is β = {(VDC / τ) * DT} * DT / 2, and the actual output voltage is reduced by this The ratio R to be compensated is R = β / α = [{(VDC / τ) * DT} * DT / 2] / {VDC * DT} = DT / (2 * τ). Therefore, the compensation amount VSET is calculated by multiplying the average dead time compensation amount VDT by this ratio R. On the other hand, in step S4, the amount of compensation VSET
Is calculated by the following formula. That is, similarly to the above, under the condition of τ> DT, the magnitude VSET of the compensation amount is obtained by VSET = VDT (1-τ / (2 * DT).

In step S5, the direction of the output current I is determined. If the direction is positive, the process proceeds to step S6, and if it is negative, the process proceeds to step S7. In step S6, the magnitude of the compensation amount V
Let SET be the compensation amount VH as it is. In step S7, a negative sign is added to the magnitude VSET of the compensation amount to obtain the compensation amount VSET.
Let H. By the above, the calculated compensation amount VH is output to the addition unit 1c.

The adder 1c is provided with the sine wave voltage command signal supplied from the sine wave voltage command generator 1a and the compensation amount V.
H and are added, and it outputs to the comparison part 1f. The comparison unit 1f is
The data supplied from the adder 1c is compared with the triangular wave carrier signal supplied from the triangular wave generator 1e to generate a PWM signal, which is supplied to the delay generator 1h and the inverter 1g.

The inversion unit 1g inverts the PWM signal supplied from the comparison unit 1f and outputs it to the delay generation unit 1h. The delay generation unit 1h inserts the dead time period DT into the PWM signal supplied from the comparison unit 1f and outputs a signal serving as a basis for driving the switching transistor Q1. Further, the inverted PWM signal supplied from the inversion unit 1g and the dead time period DT are inserted, and the switching transistor Q
It outputs the signal that is the basis for driving 2.

The operation of the U-phase controller 1 has been described above. The V-phase controller 2 and the W-phase controller 3 have been described above.
The operation of is also the same.

The drive circuit 4 comprises a U-phase controller 1, a V-phase controller 2, and a W-phase controller 3.
Switching transistor Q1 based on the signal from
~ Drive Q6.

As can be understood from the above description, in the inverter control device 100, since the compensation amount is calculated in consideration of the stray capacitance C, the switching transistor Q
Even when the switching frequency of 1 to Q6 is increased, the adverse effect due to the dead time can be suppressed appropriately.

[0030]

According to the inverter control method and the inverter control device of the present invention, the dead time compensation is performed in consideration of the stray capacitance of the switching elements and the like which form the inverter. The accuracy can be improved. That is, it is possible to reduce the output voltage drop and the waveform distortion. Therefore, it is useful in the control of the AC electric motor for holding the pressure of the injection molding machine in which the adverse effect due to the dead time is a particular problem.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a procedure for calculating a compensation amount.

FIG. 3 is a waveform diagram showing a principle of calculation of a compensation amount.

FIG. 4 is a waveform diagram of a voltage command and an actual voltage.

FIG. 5 is an explanatory diagram showing a conventional technique disclosed in Japanese Examined Patent Publication No. 59-8152.

FIG. 6 is an explanatory diagram showing a conventional technique disclosed in Japanese Patent Laid-Open No. 59-123478.

FIG. 7 is an explanatory diagram showing a conventional technique disclosed in Japanese Patent Laid-Open No. 62-239897.

[Explanation of symbols]

 1 U-phase controller 1b Compensation amount calculation part 1c Addition part 1e Triangular wave generation part 1f Comparison part 1g Inversion part 1h Delay generation part 2 V-phase controller 3 W-phase controller 5 U-phase current detector 6 V-phase current detection Device 7 W-phase current detector C Stray capacitance 100 Inverter control device IV Inverter TB Switching transistor

Claims (2)

[Claims] 1. A magnitude and a direction of an output current of an inverter are detected, and a compensation amount is calculated based on a magnitude and a direction of the output current and a magnitude of a stray capacitance of a switching element or the like constituting the inverter, and the compensation amount. An inverter control method characterized by compensating an output voltage of an inverter according to the above. 2. An output current detection means for detecting the magnitude and direction of the output current of the inverter, a magnitude and direction of the output current detected by the output current detection means, and a stray capacitance of a switching element or the like constituting the inverter. An inverter control device comprising: a compensation amount calculation means for calculating a compensation amount based on the size; and a compensation means for feeding back the compensation amount to the switching time of the switching element.