JP2006333542A - Method of controlling ac-ac direct converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of controlling an AC-AC direct converter which enables cost reduction by lowering the current rating of a direct converter by so arranging it as not to increase a motor current even in case that the rated voltage of a motor is over the saturation voltage of the DC converter such as a matrix converter or the like. <P>SOLUTION: Concerning the method of controlling the AC-AC direct converter which directly converts three-phase AC voltage into three-phase AC voltage having optional size and frequency prior to supply to the motor by means of nine pieces of AC switches connected between the input and output of three phases, an AC switch SW5 to connect the S phase with the V phase of a matrix converter 4 is kept ON and AC switches SW1 and SW2 to connect the R phase and the S phase with the U phase each are switched on or switched off alternately, and further AC switches SW1 and SW2 to connect the S phase and the T phase with the W phase each are switched on or switched off alternately. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for controlling an AC / AC direct conversion device such as a matrix converter that drives a motor at a variable speed.

FIG. 3 shows a variable speed drive system for an electric motor using a matrix converter known as this type of direct conversion device.
In FIG. 3, 1 is a three-phase AC power source, 2 is a filter reactor, 3 is a filter capacitor, 4 is a matrix converter, and 5 is an electric motor. The matrix converter 4 includes, for example, AC switches SW1 to SW9 in which two IGBTs are connected in anti-parallel so that the current can be controlled in both directions, between the input and output of each of the three phases (R, S for each phase on the input side). , T phase, and each phase on the output side are connected to U, V, and W phases). The matrix converter 4 directly converts a three-phase AC voltage into a three-phase AC voltage having an arbitrary magnitude and frequency without using a large energy buffer.

In general, when a motor is driven at a variable speed using a power converter, power conversion is performed so as to keep the ratio (V / f) between the output voltage and the output frequency constant in order to keep the magnetic flux of the motor constant. It is common to control the device.
Here, the matrix converter can generate positive and negative voltages of each phase input voltage, and the power supply voltage is directly cut out by an AC switch to output the voltage. Is within the envelope range of the six-phase alternating current shown in FIG.

  However, when the electric motor is driven by the matrix converter, the output voltage waveform may be distorted depending on the magnitude of the output voltage of the matrix converter. That is, when the matrix converter is to output a voltage exceeding 0.866 times the hatched peak value of the power supply voltage (the shaded area in FIG. 4) according to the operating state of the motor, FIG. As shown by the thick line, the line voltage Vuv is distorted in the output voltage, which causes the motor torque to pulsate and generate noise and vibration due to uneven rotation.

For this reason, it is necessary for the matrix converter to output a voltage exceeding the above-described hatched range of FIG. 4 which is 0.866 times or less, that is, a voltage exceeding a limit value of voltage that can be output without distortion (hereinafter referred to as saturation voltage). In such a case, the variable speed drive is performed by applying so-called field weakening control to the motor without applying a distorted voltage to the motor. Here, field-weakening control means that the current of the motor is separated into a component (torque current component or q-axis current component) that is orthogonal to the component parallel to the motor magnetic flux (flux current component or d-axis current component), and the magnetic flux and torque. Is a control method that expands the speed control range of the motor by controlling the output voltage of the power converter almost constant by weakening the magnetic flux current component in the high speed region.
Patent Document 1 described later describes this field-weakening control method.

FIG. 5 is an example showing the relationship of the output voltage with respect to the output frequency of the matrix converter when field weakening control is applied as a conventional technique.
As shown in the figure, in normal control, for example, the output voltage increases in proportion to the output frequency, but if the matrix converter needs to output a voltage higher than the saturation voltage as the output frequency increases, By fixing the voltage to the saturation voltage and increasing only the output frequency of the matrix converter, the field weakening control of the electric motor is performed to realize variable speed driving of the electric motor.

Japanese Patent Laid-Open No. 11-178399 (paragraphs [0005] to [0010], FIGS. 1 to 5 etc.)

By the way, as described in Patent Document 1 described above, in the case of performing field weakening control, it is necessary to increase the d-axis current in the negative direction, and as a result, the motor current increases compared to the conventional case. There is a drawback that the loss of the matrix converter and the motor increases.
Here, when the rated voltage of the motor is equal to or higher than the saturation voltage of the matrix converter, and the operation pattern of the motor is such that the rated rotation speed is maintained when the rotation speed of the motor rises to the rated rotation speed. Will continue to apply field-weakening control in the rated rotation speed region, and as the motor current increases, it is necessary to increase the current rating of the switching elements constituting the matrix converter, which causes an increase in cost. There was a problem.

  Therefore, the problem to be solved by the present invention is to reduce the current rating of the direct conversion device so as not to increase the motor current and reduce the cost even when the rated voltage of the motor is equal to or higher than the saturation voltage of the direct conversion device such as a matrix converter. It is an object to provide a method for controlling an AC / AC direct conversion device that enables the above-mentioned.

In order to solve the above-mentioned problem, the invention described in claim 1 is a three-phase AC voltage having an arbitrary magnitude and frequency by using nine AC switches connected between three-phase inputs and outputs. In the control method of the AC / AC direct conversion device for direct conversion and supply to the motor,
One AC switch that connects the first input phase and the first output phase of the converter is held in an ON state, and the first input phase, the second input phase, and the second output phase are connected to each other. The AC switches are alternately turned on and off, and two other AC switches that connect the first input phase, the third input phase, and the third output phase are alternately turned on and off.

  The invention described in claim 2 controls the output voltage so as to perform field-weakening control when outputting a voltage equal to or higher than the saturation voltage of the converter in a predetermined frequency region, and the output frequency of the converter is When the power frequency matches, the converter is controlled using the control method described in claim 1.

  In particular, the present invention is such that the rated voltage of an electric motor driven by a direct conversion device such as a matrix converter is not more than the input power supply voltage of the direct conversion device and not less than the saturation voltage of the direct conversion device, and the rated frequency of the electric motor is It is effective when it is the same as the input power frequency of the direct conversion device. Under such conditions, according to the present invention, when the motor is operated at the rated voltage and the rated frequency, it is not necessary to apply field-weakening control as in the prior art, and therefore the motor current may increase unnecessarily. Therefore, it is not necessary to increase the current rating of the direct conversion device more than necessary. Therefore, it becomes possible to reduce the current rating of the semiconductor switching element that constitutes the direct conversion device, and the cost can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 shows a first embodiment of the present invention and shows an example of an on / off pattern of each of the AC switches SW1 to SW9 constituting the matrix converter 4 of FIG.

  As shown in FIG. 1, in this embodiment, the AC switch SW5 that connects the S phase on the input side and the V phase on the output side of the matrix converter 4 is held in the ON state, and the R phase and S phase on the input side are held. AC switches SW1 and SW2 that alternately connect the output side U phase and the output side U phase are alternately turned on and off, and AC switches SW8 and SW9 that respectively connect the S phase and T phase on the input side and the W phase on the output side are similarly set. Turn on and off alternately. Here, the on / off patterns of the AC switches SW1 and SW9 and the on / off patterns of the AC switches SW2 and SW8 are the same, but the present invention is not limited to this. That is, the on / off pattern may not be the same.

When such a pulse pattern is used, the frequency of the output line voltage is made to coincide with the power supply frequency, and a line voltage having a magnitude corresponding to the ON / OFF ratio of the AC switches SW1, SW2 or AC switches SW8, SW9 is output. Can be made.
For example, when an electric motor 5 having a rated frequency equal to a power supply frequency and a rated voltage equal to or lower than the power supply voltage and equal to or higher than the saturation voltage of the matrix converter 4 is driven by the matrix converter 4 at a variable speed, as shown in FIG. By switching the matrix converter 4 like an AC chopper using a simple pulse pattern, a predetermined current can be supplied to the electric motor 5 without performing field weakening control. Therefore, an increase in the motor current can be suppressed, and the current rating of the semiconductor switching elements constituting the matrix converter 4 can be lowered to reduce the cost.

Note that the AC switch that maintains the ON state and the AC switch that repeatedly turns on and off are not limited to the example in FIG. 1. That is, when each phase on the input side of the matrix converter 4 is an arbitrary first to third input phase and each phase on the output side is an arbitrary first to third output phase, the first input phase and the first output phase Is held in an ON state, and two AC switches for connecting the first input phase, the second input phase, and the second output phase are alternately turned on and off, and What is necessary is just to turn on and off two alternating current switches which each connect 1 input phase, 3rd input phase, and 3rd output phase alternately.
For example, the AC switch SW1 that connects the R phase and the U phase in FIG. 3 is held in an ON state, and the AC switches SW4 and SW5 that connect the R phase, the S phase, and the V phase are alternately turned on and off, Needless to say, the AC switches SW7 and SW9 that connect the R phase, the T phase, and the W phase, respectively, may be alternately turned on and off, or other combinations may be used.

  Next, FIG. 2 is a second embodiment of the present invention and shows the relationship of the output voltage with respect to the output frequency of the matrix converter. This embodiment is a control method that selectively uses the conventional field-weakening control and the control method according to the first embodiment according to the output frequency.

  In the present embodiment, as shown in FIG. 2, in the region where the output frequency of the matrix converter 4 is equal to or lower than the power supply frequency and outputs a voltage equal to or lower than the saturation voltage, the normal matrix converter is controlled. In a frequency region other than the above and in a region where a voltage higher than the saturation voltage needs to be output, field weakening control is performed to suppress the output voltage of the matrix converter to the saturation voltage. Furthermore, when the output frequency of the matrix converter 4 is the same as the power supply frequency, the control method according to the first embodiment is applied without performing field-weakening control, so that the motor can be controlled at a variable speed while adjusting the output voltage. It is something to control.

  In the field weakening control region in FIG. 2, the output voltage of the matrix converter is fixed to the saturation voltage and only the output frequency is changed. However, field weakening control is not limited to such a control method. Field weakening control may be used so that the relationship with the frequency becomes another relationship. Similarly, in the normal control region at a frequency lower than the field weakening control region, another relationship other than the relationship in which the output voltage is proportional to the output frequency may be used.

  As described above, according to the second embodiment, the field-weakening control is not continued over the frequency range exceeding the power supply frequency, so that the increase in the current rating of the matrix converter 4 due to the increase in the motor current is suppressed. be able to.

It is explanatory drawing of the pulse pattern in 1st Embodiment of this invention. It is a figure which shows the relationship between the output frequency and output voltage of a matrix converter in 2nd Embodiment of this invention. It is a figure which shows the variable speed drive system of the electric motor using a matrix converter. It is a wave form diagram of the output voltage of a matrix converter. It is a figure which shows the relationship between the output frequency and output voltage of a matrix converter in the case of applying field weakening control.

Explanation of symbols

1: Three-phase AC power supply 2: Filter reactor 3: Filter capacitor 4: Matrix converter 5: Motor SW1 to SW9: AC switch

Claims (2)

A control method for an AC / AC direct conversion device for directly converting a three-phase AC voltage into a three-phase AC voltage having an arbitrary magnitude and frequency by using nine AC switches connected between the three-phase input / output and supplying the same to an electric motor In
One AC switch that connects the first input phase and the first output phase of the converter is held in an ON state, and the first input phase, the second input phase, and the second output phase are connected to each other. AC alternating current characterized in that the alternating current switches are alternately turned on and off, and two other alternating current switches that connect the first input phase, the third input phase, and the third output phase are alternately turned on and off. Control method of direct conversion device.   When outputting a voltage equal to or higher than the saturation voltage of the converter in a predetermined frequency region, the output voltage is controlled to perform field-weakening control, and the output frequency of the converter matches the power supply frequency. A control method for an AC / AC direct conversion device, wherein the conversion device is controlled using the control method according to Item 1.

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