JP2002281779A - AC motor drive - Google Patents

Abstract

[PROBLEMS] To provide a dead time compensating means capable of calculating a dead time compensation amount after grasping a change in a current polarity near a current zero crossing and minimizing a speed and a current distortion.
A C motor drive is provided. A dead time compensating means of an AC motor driving device stores a value of a current polarity PorM [Tn] in a current sampling cycle obtained by a current polarity judging means, and, when necessary, calculates a value of a previous sampling cycle. The memory device 105 capable of calling the current polarity PorM [Tn-1], the current polarity in the current sampling period (Tn), and the sampling period (Tn-1)
And a dead time compensation amount calculating means 106 for calculating a dead time compensation amount based on the current polarity of the current and the dead time compensation amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC motor driving apparatus, and more particularly to dead time compensation for a PWM inverter.

[0002]

2. Description of the Related Art In a conventional voltage source inverter, a dead time is provided in order to prevent a current short circuit accident due to simultaneous conduction of upper and lower switching elements. Although the PWM inverter has high current control performance with the number of times of switching, it is easily affected by the dead time. In particular, during low-speed and light-load operation, the influence on the current control is large, which contributes to current distortion and torque pulsation. In order to compensate for the loss voltage generated by the dead time setting of such an inverter device, first, it is necessary to accurately grasp the absolute value of the loss voltage ABSVloss by the dead time setting, which can be calculated by equation (1). The absolute value of the loss voltage can be handled as the absolute value of the dead time compensation voltage ABSVcomp. ABSVloss = ABSVcomp = td × fc × Vdc = (td / tc) × Vdc (1) where td is a dead time (on delay time), fc
Is a switching carrier frequency (= 1 / tc), tc is a switching carrier cycle time, and Vdc is a DC voltage.
In the dead time compensation method, the compensation can be performed simply from the information of the current polarity value and the absolute value of the dead time compensation voltage ABSVcomp. Is the most important processing, and accurate polarity judgment is required. In the conventional method of determining the current polarity, one of the detected current and the command current is used. FIG. 3 is an overall block diagram of a conventional dead time compensation method. 2 is a dead time compensating means according to the prior art, 11 is an AC motor, 12
Is an encoder (position sensor), 13 is current detecting means (current sensor), 14 is speed deviation calculating means, 15 is current deviation calculating means, 16 is command voltage calculating means (PI control unit), and 17 is P
WM power converter, 18 is a DC voltage, 201 is a current polarity judging means, 202 is a compensation voltage absolute value, 203 is a voltage addition calculating means, and 204 is a polarity current selecting means. The operation will be described with reference to the block diagram of FIG. Current detection means 13
Detects the current flowing to the AC motor 11 for each sampling interval, the deviation current calculation means 15 calculates the deviation current ΔI by subtracting the detection current Ifb from the command current I *, and the command voltage calculation means 16 calculates the deviation current ΔI The command voltage V * is calculated by multiplying by the control gain. Further, the polarity current selection means 204 selects the detection current of the current sampling period as the polarity determination current, and the current polarity determination means 201 determines the current polarity using the polarity determination current Ip [Tn]. The value PorM (the value of +1 or -1) is calculated as the compensation voltage absolute value A.
BSVcomp is multiplied to calculate a dead time compensation voltage Vcomp. Lastly, the dead time compensation voltage Vcomp is added to the command voltage V * by the voltage addition calculating means 203 to calculate the final command voltage Vf *, which is input to the PWM power converter 17,
The AC motor 11 is driven.

[0003]

In the prior art, the current polarity is determined from the detected current in the current sampling period,
The dead time compensation value is processed according to the result. However, since the detected current actually includes switching noise, it is difficult to accurately determine the current polarity near the current zero cross. Since the over-correction is easily caused by the dead time compensation, there is a problem that the speed and the current characteristic (current distortion) are more adversely affected than when the dead time compensation is not performed. The present invention has been made in order to solve the above problem, and calculates the amount of dead time compensation after grasping the fluctuation of the current polarity near the current zero crossing, and can minimize the speed and the current distortion. It is an object of the present invention to provide an AC motor driving device having dead time compensation means.

[0004]

In order to solve the above-mentioned problems, the present invention of claim 1 comprises a current detecting means for detecting a current flowing to an AC motor, and a deviation detecting means for calculating a deviation current from a command current and a detected current. Current calculation means, command voltage calculation means for calculating a command voltage from the deviation current, polarity current selection means for selecting a detection current in the current sampling period detected by the current detection means as a polarity determination current, and the polarity A dead time compensating means for outputting a dead time compensating voltage; a dead time compensating means for adding the dead time compensating voltage to the command voltage calculated by the command voltage calculating means; Voltage addition operation means for calculating a voltage, and conversion from a DC voltage, which is a final command voltage obtained by the voltage addition operation means, to an AC voltage. In the AC motor driving device having the PWM power converter, the dead time compensating means stores the value of the current polarity PorM [Tn] in the current sampling period obtained by the current polarity determining means, and Memory device that can call the current polarity PorM [Tn-1] of the previous sampling period and the current sampling period (T
n) and dead time compensation amount calculating means for calculating a dead time compensation amount from the current polarity of the previous sampling period (Tn-1), and a dead time compensation voltage based on the result of the dead time compensation amount. Is calculated. In addition, the dead time compensation amount calculating means includes:
When the current polarity in the current sampling cycle is the same as the current polarity in the previous sampling cycle (sign (current [Tn]) = sign (current [Tn-1])),
A step of setting the dead time compensation amount to a negative value of -1 and a positive value of +1 as a judgment value in the current polarity of the current sampling period, and a case where the current polarity of the current sampling period is different from the current polarity of the previous sampling period (sign (Current [Tn])
≠ sign (current [Tn-1]) includes a step of setting the dead time compensation amount to a value obtained by multiplying the judgment value of the current polarity in the current sampling period or the previous sampling period by 0 to 1. It is a feature.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall block diagram relating to a dead time compensation method showing an embodiment of the present invention. FIG. 2 is a flowchart showing a dead time compensation method according to an embodiment of the present invention. In FIG. 1, 1 is a dead time compensating means according to the present invention, 101 is a current polarity determining means, 102 is a compensation voltage absolute value, 103 is a voltage addition calculating means, 104 is a polarity current selecting means, and 105 is a current polarity. Or a memory device that makes calls. Note that the current detecting means 13
And deviation current calculating means 15 and command voltage calculating means 16
, Polarity current selection means 104, current polarity determination means 10
1 is the same as that of the prior art. The differences between the present invention and the prior art are as follows. That is,
The dead time compensating means 1 stores the value of the current polarity PorM [Tn] in the current sampling cycle obtained by the current polarity judging means 101 and, when necessary, the current polarity in the previous sampling cycle.
Memory device 105 capable of calling PorM [Tn-1]
And a current polarity in the current sampling period (Tn) and a current polarity in the sampling period (Tn-1) to calculate a dead time compensation amount.
And the dead time compensation voltage is calculated from the result of the dead time compensation amount. When the current polarity of the current sampling cycle is the same as the current polarity of the previous sampling cycle (sign (current [Tn]) = sign (current [Tn-1])), the dead time compensation amount calculating means 106 determines that A step of setting the time compensation amount to a negative value of -1 and a positive value of +1 as a judgment value in the current polarity of the current sampling period, and a case where the current polarity of the sampling period is different from the current polarity of the previous sampling period (sign (current [Tn]) ≠ sig
For n (current [Tn-1])), the dead time compensation amount is set to a value equal to or less than a necessary compensation value, that is, a value obtained by multiplying the judgment value in the current polarity in the current sampling period or the previous sampling period by 0 to 1. And a stage.

With respect to the above-mentioned dead time compensating means, the procedure is described based on FIG.
This will be described with reference to FIG. (Step F1): The polarity current selection means 104 selects the detection current Ifb [Tn] in the current sampling cycle as the polarity determination current Ip [Tn] in the current sampling cycle. (Step F2): The current polarity judging means 101 calculates a current polarity value PorM [Tn] from the polarity judgment current Ip [Tn]. Here, the determination of the current polarity "+ if the detected current is greater than 0,
If it is less than 1, 0, -1 is output ". (Step F3): The current polarity PorM [Tn-1] of the previous sampling period is called from the memory device 105, and the current polarity PorM [Tn] of the current sampling period is stored in the memory device 105. (Step F4): The current polarity value PorM [Tn] (a value of +1 or -1) in the current sampling cycle obtained in Step F2,
Using the current polarity value PorM [Tn-1] in the previous sampling period called from the memory device 105 obtained in step F3, the dead time compensation amount PorMorZ is calculated in the following step F5.
1 and calculation as in step F52. (Step F51): Dead time compensation amount calculation means 10
6, the current polarity PorM [T
n] is the same as the current polarity PorM [Tn-1] in the previous sampling period (sign (current [Tn]) = sign (current [Tn-1])), the dead time compensation amount PorMorZ is set to sign (current [Tn] ]) (Step F52): Dead time compensation amount calculating means 10
6, the current polarity PorM [T
n] is different from the current polarity PorM [Tn-1] of the previous sampling period (sign (polarity determination current [Tn]) ≠ sign (polarity determination current [Tn-1])), the dead time compensation amount PorMorZ is calculated. Set to zero value. Here, the dead time compensation amount PorMorZ is a value of −1 to +1.
I made it. (Step F6): The dead time compensation voltage is calculated from the dead time compensation amount PorMorZ and the compensation voltage absolute value. (Step F7): The voltage addition arithmetic unit 103 calculates the final command voltage Vf * by adding the dead time compensation voltage Vcomp to the command voltage V *, and inputs it to the PWM power conversion device 17.

Therefore, the dead time compensating means 1 according to the present embodiment stores the value of the current polarity PorM [Tn] in the current sampling period obtained by the current polarity judging means 101, and stores the value of the previous sampling period when necessary. The memory device 105 capable of calling the current polarity PorM [Tn-1], the current polarity in the current sampling period (Tn), and the calculation of the dead time compensation amount are calculated from the current polarity in the sampling period (Tn-1). And a dead time compensation amount calculating means 106 for performing
Since the dead time compensation voltage is calculated from the result of the dead time compensation amount, the influence of the switching noise included in the polarity determination current can be minimized, and the dead time compensation near the current zero cross can be optimized. As a result, current distortion and velocity ripple can be minimized. In the present embodiment, the detection current Ifb is used as an index for determining the current polarity, but the command current I * may be used instead of the detection current.
Further, the dead time compensation amount calculation means 1 in step F52
In 06, when the current polarity in the current sampling period is different from the current polarity in the previous sampling period, the dead time compensation amount is set to zero, but the present invention is not limited to this, and may be set to any value. .

[0008]

As described above, according to the present invention, the dead time compensating means stores the value of the current polarity PorM [Tn] in the current sampling period obtained by the current polarity judging means 101, and Sometimes the current polarity of the previous sampling period PorM [T
n-1], the dead time compensation amount for calculating the dead time compensation amount from the current polarity in the current sampling period (Tn) and the current polarity in the sampling period (Tn-1). Computation means and dead time compensation voltage are calculated from the result of the dead time compensation amount, minimizing the effect of switching noise included in the polarity judgment current and optimizing dead time compensation near the current zero crossing. Can be As a result, there is an effect that current distortion and speed ripple can be minimized.

[Brief description of the drawings]

FIG. 1 is an overall block diagram relating to a dead time compensation method showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a dead time compensation method according to an embodiment of the present invention.

FIG. 3 is an overall block diagram of a conventional dead time compensation method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Dead time compensating means (the present invention) 2 Dead time compensating means (prior art) 11 AC motor 12 Encoder (position sensor) 13 Current detecting means (current sensor) 14 Speed deviation calculating means 15 Current deviation calculating means 16 Command voltage calculating means (PI control unit) 17 PWM power converter 18 DC voltage 101, 201 Current polarity determination means 102, 202 Compensation voltage absolute value (dead time compensation voltage calculation means) 103, 203 Voltage addition calculation means 104, 204 Polarity current selection means 105 Memory device / memory calling unit / memory storage unit 106 Dead time compensation amount calculation unit * Subscript representing command I * Command current Vdc Smooth DC voltage of inverter V * Command voltage Vf * Final command voltage Ifb Detection current ΔI Deviation current Ip Polarity judgment Current ωfb Detection speed θfb Detection position td Dead tie Time fc Switching carrier frequency (= 1 / tc) tc Switching carrier cycle time Tn Current sampling cycle Tn-1 Previous sampling cycle ABS Absolute value ABSVloss Loss voltage absolute value ABSVcomp Compensation voltage absolute value Vcomp Dead time compensation voltage PorM Current polarity value ( -1 or +1) PorM [Tn] Current polarity value of current sampling period PorM [Tn-1] Current polarity value of previous sampling period PorMorZ Dead time compensation amount (arbitrary value of -1 to +1) sign () Sign judgment function

Claims (2)

[Claims] 1. A current detection means for detecting a current flowing to an AC motor, a deviation current calculation means for calculating a deviation current from a command current and a detection current, and a command voltage calculation means for calculating a command voltage from the deviation current And a polarity current selection means for selecting a detection current in the current sampling period detected by the current detection means as a polarity determination current, and a current polarity determination means for determining a current polarity from the polarity determination current, and a dead time compensation voltage. , A voltage addition operation means for adding the dead time compensation voltage to the command voltage calculated by the command voltage operation means to calculate a final command voltage, and a voltage addition operation means for obtaining a final command voltage. A PWM power converter that converts a DC voltage, which is the final command voltage, into an AC voltage. The dead time compensating means stores the value of the current polarity PorM [Tn] in the current sampling cycle obtained by the current polarity judging means, and stores the current polarity PorM [Tn-1 in the previous sampling cycle when necessary. And a dead time compensation amount calculating means for calculating a dead time compensation amount from the current polarity in the current sampling period (Tn) and the current polarity in the previous sampling period (Tn-1). An AC motor drive device comprising: calculating a dead time compensation voltage from a result of the dead time compensation amount. 2. The dead time compensation amount calculating means, wherein the current polarity of the current sampling cycle is the same as the current polarity of the previous sampling cycle (sign (current [Tn]) = sign (current [T
n-1])), the dead time compensation amount is determined as a judgment value in the current polarity of the current sampling cycle by -1 for negative and +1 for positive.
And when the current polarity of the current sampling cycle is different from the current polarity of the previous sampling cycle (sign
(Current [Tn]) ≠ sign (current [Tn-1])), the dead time compensation amount is set to a value obtained by multiplying the judgment value in the current polarity of the current sampling period or the previous sampling period by 0 to 1. The AC motor driving device according to claim 1, further comprising: