JP2002272182A - AC motor drive - Google Patents

Abstract

(57) Abstract: An AC motor drive having dead time compensating means capable of finding a polarity judging current not including phase delay and switching noise over a wide range of speeds and minimizing speed and current distortion. Provide equipment. A dead time compensating means of an AC motor driving device includes: a bandwidth range determining means for determining whether a detected current Ifb is within or outside a range of a bandwidth provided near a current zero cross; When the range judging means 104 judges that the detection current Ifb is within the range of the bandwidth, the detection current Ifb is switched (FON) so as to be filtered by the filter 107 and output to the current polarity judgment means 101. A switching unit for performing switching (FOFF) such that when it is determined that the current Ifb is outside the range of the bandwidth, the detection current Ifb is output to the current polarity determination unit 101 without being filtered by the filter 107;

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, any one of a detection current, a command current, and a filtering detection current is used. FIG. 5 is an overall block diagram of a conventional dead time compensation method. 2 is dead time compensating means, 11 is A
C motor, 12 is an encoder (position sensor), 13 is current detection means (current sensor), 14 is speed deviation calculation means, 15 is current deviation calculation means, 16 is current control section (PI control section),
17 is a PWM power converter, 18 is a DC voltage, 201 is current polarity judging means, 202 is an absolute value of compensation voltage, 203 is voltage addition calculating means, 204 is a filter, and 205 is polarity current selecting means. The operation will be described with reference to the block diagram of FIG. The 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 current control section 16 calculates the deviation current ΔI. The command voltage V * is calculated by multiplying the current ΔI by a gain. Further, the detection current Ifb, the command current I *,
One of the filtering detection currents Ifbf is selected as the polarity determination current Ip, and the current polarity determination unit 201 determines the current polarity using the polarity determination current Ip, and then determines the current polarity value PorM (+1 or −1). ) Is multiplied by the compensation voltage absolute value ABSVcomp to calculate the dead time compensation voltage Vcomp.
Is calculated. 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 conversion device 17 to drive the AC motor 11. I have.

[0003]

However, in the prior art, the detection current, the command current, and the filtering detection current used as the polarity determination current have the following problems. (1) In the case of the detected current, since switching noise is included, a determination error of the current polarity is likely to occur near the zero cross. (2) In the case of the command current, the higher the frequency of the current in accordance with the speed, the larger the phase difference with the detection current, which is not desirable as the polarity determination current. (3) The filtering detection current is a current obtained by removing switching noise from the detection current with a low-pass filter, and the phase difference from the actual current may increase due to the setting of the filter time constant. Therefore, by using the polarity determination current, the polarity of the current cannot be properly determined, and the dead time cannot be compensated correctly. 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. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and can determine a polarity determination current that does not include phase delay and switching noise over a wide range of speeds (frequency), and minimizes speed and current distortion. It is an object of the present invention to provide an AC motor driving device having a dead time compensating means that can perform the above.

[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. A dead time for outputting a dead time compensation voltage, comprising: a current calculation unit; a current control unit for calculating a command voltage from the deviation current; a filter for filtering the detection current; and a current polarity determination unit for determining a current polarity. Compensating means, voltage adding operation means for calculating the final command voltage by adding the dead time compensation voltage to the command voltage calculated from the current control section, and DC as the final command voltage obtained by the voltage adding operation means And a PWM power converter for converting a voltage to an AC voltage. Bandwidth range determining means for determining whether the current is within or outside the range of the bandwidth provided near the current zero crossing, and that the detected current is within the range of the bandwidth by the bandwidth range determining means. When it is determined, the detection current is filtered by a filter and switching (FON) is performed so as to output the current to the current polarity determination means. When it is determined that the detection current is out of the bandwidth range, the FON is performed. Switching means for switching (FOFF) so that the detected current is output to the current polarity judging means as it is without being filtered by a filter. Claim 2
According to the present invention, in the AC motor driving apparatus according to claim 1, a low-pass filter is used as the filter, and a filter time constant calculating means for automatically calculating a filter time constant according to a command speed or a detection speed; Memory·
A calling means is provided. According to a third aspect of the present invention, in the AC motor driving device according to the first aspect, the initial value of the filter is always set between the switching means and the current polarity determining means when the output from the band range determining means is FOFF. A reset means for resetting is provided.

[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 according to a first embodiment of the present invention. 1, reference numeral 1 denotes a dead time compensating means according to the present invention;
1 is a current polarity judging means, 102 is an absolute value of a compensation voltage, 10
3 is a voltage addition calculating means, 104 is a bandwidth range determining means, 105 is a switching means (switch), 106 is a filter time constant calculating means and storing / calling means, 107 is an LPF
(Low-pass filter) and 108 are reset means for resetting the filter initial value. The current detection means 13 detects the current flowing to the AC motor 11 for each sampling interval, and the deviation current calculation means 15 calculates the deviation current ΔI by subtracting the detection current Ifb from the command current I *. The configuration in which the command voltage V * 16 calculates the command voltage V * by multiplying the deviation current ΔI by the gain is the same as the conventional technology. The differences between the present invention and the prior art are as follows. The dead time compensating means 1 includes a bandwidth range determining means 104 for determining whether or not the detected current is within or outside the range of the bandwidth provided near the current zero crossing. Is determined to be within the bandwidth range, the detection current Ifb is filtered by the filter 107 and switched to output to the current polarity determination means 101 (FO).
N), when it is determined that the detection current Ifb is outside the range of the bandwidth, the switching (FOFF) is performed so that the detection current Ifb is output to the current polarity determination unit 101 without being filtered by the filter. And a means 105 (switch). Also, an LPF (low-pass filter) is used as the filter 107. The filter time constant is automatically calculated and stored according to the command speed or the detected speed, and when the filter time constant is called from the filter 107. The filter 107 is provided with a filter time constant calculating means for transmitting a signal of the filter time constant and a storage / recall means 106. Further, between the switching means 105 and the current polarity determining means 101,
A reset means 108 is provided for always resetting the initial value of the filter 107 when the output from the bandwidth range determining means 104 is FOFF. Here, FIG.
It is a current waveform flowing to the C motor 11 and has a set bandwidth. The filter time constant is different depending on the speed frequency in each sampling section, and the above-mentioned bandwidth range determining means 104 performs filtering according to the speed frequency.

The procedure for the dead time compensation method described above will be described based on FIG. 3 and with reference to FIG. FIG. 3 is a flowchart relating to the dead time compensation method according to the first embodiment. (Step A1) An arbitrary bandwidth is set near the current zero crossing, an initial value (reset) of the filter, and a filter time constant τ are set by a bandwidth setting means (not shown). (Step A2) The detected current Ifb is compared with the bandwidth by the bandwidth range determining means 104. As a result, when the band width range judging unit 104 judges that the detected current Ifb is within the range of the bandwidth, the FON is switched. When it is judged that the band is out of the range, the switching of FOFF is executed by the switching unit 105 (switch). Do with. If it is within the bandwidth, the processing of steps A31 to A32 is performed, and if it is not the bandwidth, the processing of steps A41 to A44 is performed. (Step A31) The filter time constant τ is called from the memory of the filter time constant calculation means and the storage / calling means 106. (Step A32) The detected current Ifb is input to the low-pass filter 107 having the time constant τ to calculate the polarity judging current Ip. (Step A41) The detected current Ifb is calculated as it is as the polarity judging current Ip, and the initial value of the filter is reset. Reset by means 108. (Step A42) The filter time constant calculation means and the storage / recall means 106 calculate the time constant τ of the low-pass filter from the speed (command speed, detected speed). (Step A43) The filter time constant τ obtained in step A42 is stored in the memory of the filter time constant calculation means and the memory / recall means 106. (Step A44) The detected current is calculated as it is as the polarity judging current. (Step A5) The current polarity determining means 101 calculates the value of the current polarity PorM from the polarity determination current Ip. (Step A6) Current polarity value PorM (+1 when positive,
If negative, -1) is multiplied by the compensation voltage absolute value ABSVcomp to calculate the dead time compensation voltage Vcomp. (Step A7) The dead time compensation voltage Vcomp is added to the command voltage V * obtained by the current control unit 14, and a final command voltage to be input to the PWM power converter is calculated.

[0007] Therefore, in the first embodiment, the dead time compensating means 1 determines whether the detected current is within or outside the range of the bandwidth provided near the current zero crossing. When the band width determination means 104 determines that the detection current Ifb is within the range of the bandwidth, the detection current If
The filter 107 is switched (FON) so that the current b is filtered by the filter 107 and output to the current polarity determining means 101. When the detected current Ifb is determined to be out of the bandwidth range, the detected current Ifb is filtered by the filter 107. A switching means 105 (switch) for performing switching (FOFF) so as to directly output the current polarity to the current polarity determining means 101 without performing the operation, so that a low-pass filter having a time constant according to the bandwidth and speed provided near the zero crossing is provided. By using, it is possible to obtain from the detection current a polarity determination current that does not include phase lag and switching noise in a wide range of speeds (frequency), correctly determine the current polarity from the polarity determination current, and minimize the speed and current distortion. There is an effect that can be made.

Next, a second embodiment of the present invention will be described. The difference between the second embodiment and the first embodiment is that the first embodiment compares the detected current Ifb with the bandwidth when the bandwidth range determining means 104 compares the detected current Ifb with the bandwidth in step A2. After switching the FON when it is determined to be within the range, a process for calling the filter time constant τ from the memory is performed in step A31, and when it is determined that the filter is out of the bandwidth range, the FOFF is switched. In contrast to the calculation of the new filter time constant, the second embodiment does not calculate a new filter time constant at the time of switching FOFF, but calculates and uses a new filter time constant at the time of switching FON. It is a point that was made. Thus, it is not necessary to save the filter time constant τ in the memory when the FOFF is switched, and it is possible to immediately calculate a new filter time constant when the FON is switched.

FIG. 4 is a flowchart relating to a dead time compensation method according to a second embodiment of the present invention. (Step B1) An arbitrary bandwidth is set near the current zero crossing, and an initial value (reset) of the filter is set by a bandwidth setting means (not shown). (Step B2) The band width determination means 104 compares the detected current Ifb with the band width. As a result, when the band width range judging unit 104 judges that the detected current Ifb is within the range of the bandwidth, the FON is switched. When it is judged that the band is out of the range, the switching of FOFF is executed by the switching unit 105 (switch). Do with. If it is within the bandwidth, the processing of steps B31 to B32 is performed, and if it is not the bandwidth, the processing of steps B41 to B42 is performed. (Step B31) The time constant τ of the low-pass filter is calculated from the information on the speed (command speed or detected speed) by the filter time constant calculation means and the storage / recall means 106. (Step B32) The detection current Ifb is input to the low-pass filter 107 having the time constant τ, and the polarity determination current Ip is calculated. (Step B41) The detection current Ifb is calculated as it is as the polarity determination current Ip, and the initial value of the filter is reset by the reset unit 108. (Step B42) The detection current Ifb is converted to the polarity determination current I
Calculate as p. (Step B5) The current polarity determining means 101 calculates the value of the current polarity from the polarity determining current Ip. (Step B6) Current polarity value PorM (+1 if positive,
If negative, -1) is multiplied by the compensation voltage absolute value ABSVcomp to calculate the dead time compensation voltage Vcomp. (Step B7) In addition to the command voltage V * obtained by the current control unit 14, the dead time compensation voltage Vcomp is used to calculate a final command voltage to be input to the PWM power converter.

In the second embodiment, basically, a dead time compensation method similar to that of the first embodiment is configured. Therefore, a low-pass filter provided near the zero cross and having a time constant according to the bandwidth and speed is used. By using it, it is possible to obtain from the detected current a polarity determination current that does not include phase lag and switching noise in a wide range of speeds (frequency), correctly determine the current polarity from the polarity determination current, and minimize speed and current distortion. Needless to say, there is an effect that can be done. In step A44 of the first embodiment and step B42 of the second embodiment, the detection current Ifb is used as an index for judging the current polarity, but the command current I * is used instead of the detection current. It does not matter.

[0011]

As described above, according to the present invention, by using a low-pass filter having a time constant corresponding to the bandwidth and the speed provided near the zero cross, the phase delay and the switching at a wide range of speeds (frequency) can be achieved. The polarity determination current that does not include noise can be obtained from the detected current, and the polarity of the current can be correctly determined from the polarity determination current, and the speed and current distortion can be minimized.

[Brief description of the drawings]

FIG. 1 is an overall block diagram related to a dead time compensation method according to a first embodiment of the present invention.

FIG. 2 is a current waveform in which a bandwidth is set.

FIG. 3 is a flowchart relating to a dead time compensation method according to the first embodiment of the present invention.

FIG. 4 is a flowchart relating to a dead time compensation method according to a second embodiment of the present invention.

FIG. 5 is an overall block diagram of a conventional dead time compensation method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Dead time compensation means (this invention) 11 AC motor 12 Encoder (position sensor) 13 Current detection means (current sensor) 14 Speed deviation calculation means 15 Current deviation calculation means 16 Current control unit (PI control unit) 17 PWM power conversion device 18 DC voltage 101 Current polarity judging means 102 Compensation voltage absolute value 103 Voltage adding calculating means 104 Bandwidth range judging means 105 Switching means (switch) 106 Filter time constant calculating means and storing / calling means 107 LPF 108 Reset means (Filter initial value) * Reset means of command) * Subscript representing command Vdc DC voltage of inverter V * Command voltage Vf * Final command voltage I * Command current Ifb Detection current ΔI Deviation current Ip Polarity judgment current ω Speed ωfb Detection speed θ position θfb Detection position τ Filter Constant td dead time time fc switching key Carrier frequency (= 1 / tc) tc switching carrier cycle time ABS absolute value ABSVloss loss voltage absolute value ABSVcomp compensation voltage absolute value LPF low-pass filter Vcomp dead time compensation voltage PorM Current polarity value (+1 for positive, negative for negative −
1) Signal to fsgnl SW (PON or POFF)

Claims (3)

[Claims] 1. A current detecting means for detecting a current flowing to an AC motor, a deviation current calculating means for calculating a deviation current from a command current and a detected current, and a current control unit for calculating a command voltage from the deviation current. A filter for filtering the detected current and a current polarity determining means for determining a current polarity; a dead time compensating means for outputting a dead time compensating voltage; and a dead time compensating means for calculating a command voltage calculated from the current control unit. AC comprising: a voltage addition calculating means for calculating a final command voltage by adding a voltage; and a PWM power converter for converting a DC voltage, which is a final command voltage obtained by the voltage addition calculating means, into an AC voltage. In the motor driving device, the dead time compensating means may be configured such that the detected current is within a range of a bandwidth provided near a current zero crossing or A bandwidth range determining means for determining whether the detected current is outside the range, and when the detected current is determined to be within the range of the bandwidth by the bandwidth range determining means, the detected current is filtered by a filter. Then, switching (FON) is performed so as to output the current to the current polarity judging means. When it is judged that the detected current is out of the range of the bandwidth, the detected current is not filtered by a filter but the current is directly filtered. An AC motor driving device, comprising: switching means for performing switching (FOFF) so as to output to the polarity determining means. 2. A low-pass filter is used as the filter, and a filter time constant calculating means for automatically calculating a filter time constant according to a command speed or a detection speed and a storage / recall means are provided. The AC motor driving device according to claim 1. 3. A resetting means is provided between the switching means and the current polarity judging means for always resetting an initial value of a filter when an output from the band range judging means is FOFF. 2. The AC motor driving device according to 1.