JP4029282B2 - AC / AC direct conversion power converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides an AC / AC direct conversion power converter (hereinafter simply referred to as needed) that directly converts AC power to AC power to obtain a desired output voltage and / or output frequency without a large energy buffer. In particular, the present invention relates to a power conversion device having a function of avoiding an abnormal situation in which a load current becomes an overcurrent.
[0002]
[Prior art]
FIG. 6 is a control block diagram of a conventional direct conversion type power converter having a processing function when this kind of abnormal situation occurs.
In FIG. 6, 10 is a voltage command generating means for generating a voltage command having a predetermined amplitude and frequency, and 11 is a power supply voltage detected by the voltage detector 13 and a load current detected by the current detector 14 based on the voltage command. PWM generating means for generating a switching pattern (PWM pattern) according to, 16 is a changeover switch, 20 is a power source such as a three-phase AC power supply, 30 is a direct converter that performs AC-AC direct conversion, and 40 is an AC motor or the like. It is a load.
In the direct converter 30, the switching pattern depends on the power supply voltage because the voltage to be switched is alternating current. Accordingly, the power supply voltage is detected by the voltage detector 13 and a switching pattern corresponding to the voltage command is generated.
[0003]
Reference numeral 15 denotes an abnormality detecting means for detecting an abnormality such as an output overcurrent by the current detector 14 and switching the changeover switch 16 to the abnormality processing side. Reference numeral 12 denotes an output overcurrent, load temperature overheating, cooling It is an abnormality processing means for outputting a switching pattern for directly turning off the direct converter 30 to the changeover switch 16 side when an abnormality such as fan overheating occurs.
[0004]
Here, a typical example of the direct converter 30 is a three-phase matrix converter shown in FIG. That is, in FIG. 7, one end of each of the bidirectional switches S1, S4, S7 is connected to the input terminal R on the power source side, and one end of each of the bidirectional switches S2, S5, S8 is connected to the input terminal S. One end of each of the bidirectional switches S3, S6, S9 is connected to the terminal T. The other ends of the bidirectional switches S1 to S3 are collectively connected to the output terminal U on the load side, and the bidirectional switches S4 to S6. The other ends are collectively connected to the output terminal V, and the other ends of the bidirectional switches S7 to S9 are collectively connected to the output terminal W.
[0005]
As shown in parentheses in FIG. 7, the bidirectional switches S1 to S9 connect semiconductor switching elements Sa and Sb such as IGBTs having diodes Da and Db connected in reverse parallel, in reverse series, or have reverse breakdown voltage capability. If there is, only the semiconductor switching elements Sa and Sb are connected in antiparallel.
[0006]
In this type of direct converter 30, when the load 40 is an inductive load, when the load end is opened, a surge voltage is generated at both ends of the semiconductor switching element inside the converter by the energy accumulated in the reactor of the load 40. Then, the switching element is destroyed.
In order to prevent the destruction of the element due to such an open load end or short circuit of the power source, the direct conversion type power converter of FIG. 6 uses one unidirectional switch using two unidirectional switching elements as shown in FIG. In addition, the PWM generating means 11 generates nine switching patterns according to the polarity of the power supply voltage and the load current, and directly converts into 18 gate patterns in the converter 30 for operation.
[0007]
As a prior art document, a drive control device that drives a synchronous motor using a matrix converter is described in, for example, Patent Document 1 described later.
In addition, a power converter that drives an AC motor by directly converting an AC power supply voltage into an AC voltage having a different frequency and amplitude by a PWM cycloconverter including a bidirectional switching means is described in Patent Document 2 described later. This document discloses a technique for preventing the switching element from being destroyed due to an overcurrent in the charging operation of the snubber capacitor.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-18489 (FIG. 1)
[Patent Document 2]
Japanese Patent Application Laid-Open No. 11-262264 (FIGS. 1, 6 to 8, [0010], [0015] to [0017])
[0009]
[Problems to be solved by the invention]
In the prior art shown in FIG. 6, the operation of the direct converter 30 is stopped by the abnormality processing means 12 when an overcurrent occurs.
However, depending on the application, it may be required to continuously operate the direct converter 30 without stopping it as much as possible. Even if the output voltage command is obtained simply by feedback control and the output current of the converter is controlled directly, the limitation of the current command used for feedback control may cause control delay or transient overshoot. Eventually, an overcurrent may occur, and the direct converter may stop.
When the direct converter stops its operation in this manner, it causes a sudden change in the load. Therefore, when the mechanical device is connected to an electric motor driven by the direct converter, the mechanical device may be damaged. .
[0010]
Therefore, the present invention provides a direct conversion type power that enables continuous operation of a direct converter by quickly detecting a dangerous state in the previous stage of occurrence of overcurrent and selecting a switching pattern that reduces the load current. A conversion device is to be provided.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, an invention according to claim 1 is an AC-AC direct conversion type power conversion device including a direct converter that directly converts AC power into AC power using a semiconductor switching element.
Current detection means for detecting a load current of the direct converter;
Comparison means for comparing at least one phase current level of the load current detected by the current detection means with a current limit level smaller than the overcurrent level;
When the comparison means detects that the one phase current level exceeds the current limit level, an output voltage level in a direction almost opposite to the direction of the load current vector is set to reduce the phase current. Load current limiting means for selecting and driving the direct converter with a switching pattern corresponding to the output voltage level.
[0012]
The invention according to claim 2 is an AC-AC direct conversion type power conversion device including a direct converter that directly converts AC power into AC power using a semiconductor switching element.
Current detection means for detecting a load current of the direct converter;
Comparison means for comparing at least one phase current level of the load current detected by the current detection means with a current limit level smaller than the overcurrent level;
When the comparison means detects that the one phase current level exceeds the current limit level, in order to decrease the phase current, the direction of the phase current vector exceeding the current limit level is substantially Load current limiting means for selecting an output voltage vector in the opposite direction and driving the direct converter with a switching pattern corresponding to the output voltage level .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a control block diagram showing an embodiment of the present invention. The same components as those in FIG. 6 are denoted by the same reference numerals and the description thereof will be omitted. Hereinafter, different parts will be mainly described.
[0015]
In FIG. 1, reference numeral 17 denotes a load current of each phase detected by the current detector 14 and a power supply voltage of each phase detected by the voltage detector 13, and outputs a predetermined pulse pattern for limiting the load current. The load current limiting means 18 is a comparison means for outputting the control signal for the load current limiting means 17 and the second change-over switch 19 described below when the load current of each phase and the current limit level are inputted. And a switching pattern from the load current limiting means 17 or a switching pattern from the PWM generating means 11 is output to the first changeover switch 16 side.
The first changeover switch 16 substantially corresponds to the changeover switch 16 of FIG. 6 and switches between the switching pattern input via the second changeover switch 19 and the switching pattern from the abnormality processing means 12. To the converter 30 directly.
[0016]
In this direct conversion type power converter, the second changeover switch 19 is connected to the PWM generating means 11 side and the first changeover switch 16 is connected to the second changeover switch 19 side in normal times. Based on the voltage command output from the voltage command generation means 10, the PWM generation means 11 outputs a switching pattern corresponding to the power supply voltage and load current at that time, and this switching pattern is output to the second changeover switch 19 and the first changeover switch 19. By directly supplying the converter 30 via the changeover switch 16, the semiconductor switching element is switched to supply predetermined AC power to the load 40.
[0017]
Now, as the magnitude of the load current, a current limit level lower than the overcurrent level corresponding to the abnormal situation is set in the comparison means 18, and the current limit level and the magnitude of the load current are set for each phase by the comparison means 18. Shall be compared.
If the load current of a certain phase becomes larger than the current limit level, the comparison means 18 sends limit current phase information (information on which phase of the load current exceeds the current limit level) to the load current limit means 17 and A pulse pattern at the time of limiting the load current for the phase is output, and the second changeover switch 19 is switched to the load current limiting means 17 side by a control signal from the comparison means 18.
At this time, since the level of the load current is smaller than the overcurrent level, the abnormality detection means 15 that detects the overcurrent and switches the first changeover switch 16 to the abnormality processing means 12 side is not operating, and the first changeover is not performed. The switch 16 is connected to the second changeover switch 19 side.
[0018]
Therefore, a pulse pattern that reduces the load current of a certain phase to be below the current limit level is output from the load current limiting means 17 and directly applied to the converter 2 via the second and first changeover switches 19 and 16. By driving, the magnitude of the load current of a certain phase can be limited to a desired level or less when it does not reach the overcurrent.
[0019]
FIG. 2 is a block diagram showing a first embodiment of the load current limiting means 17. The load current limiting means 17 includes a load current vector detecting means 171 that receives the load current vector of each phase and detects its angle, and an output voltage vector pattern calculating means 172 that detects an output voltage vector pattern from the power supply voltage vector. The output voltage vector in the opposite direction to the load current vector of each phase is selected as a limit voltage vector, and the limit voltage vector selection means 173 generates a switching pattern corresponding to this voltage vector.
[0020]
Here, FIG. 3 shows a distribution of output voltage vectors of a three-phase matrix converter as the direct converter 30, and there are 24 types of voltage vectors depending on the switching pattern. The circles in FIG. 3 are the tips of the voltage vectors.
For example, if the load current vector when the current of a certain phase exceeds the current limit level is i _out , the limit voltage vector selection means 173 has a magnitude in a direction almost opposite to the load current vector i _out . The maximum voltage vector v _out (the tip of this voltage vector is indicated by ●) is selected, and the corresponding switching pattern is output. As a result, the load current vector i _out decreases, so that the operation can be continued while limiting the load current below the current limit level.
[0021]
In the case of the direct converter 30, each output voltage vector changes with the movement of the power supply voltage vector. Therefore, in order to reduce the current more effectively, the output voltage vector (limit voltage vector) to be used is switched according to the power supply voltage, and the voltage vector opposite to the direction of the current vector is constantly selected and the corresponding switching is performed. A pattern may be output.
[0022]
FIG. 4 is a block diagram showing a second embodiment of the load current limiting means. Here, the load current limiting means is denoted by reference numeral 17 '.
Reference numeral 17 'denotes a load current limiting means, which is composed of a current vector detecting means 171, an output voltage vector pattern calculating means 172, and a limiting voltage vector selecting means 174. The limiting voltage vector selecting means 174 includes the comparing means 18 shown in FIG. The output limited current phase information is input.
In the second embodiment, the limit voltage vector selection unit 174 selects the voltage vector v _out having the maximum magnitude in the opposite direction to the current vector of the phase exceeding the current limit level among the load current vectors. The corresponding switching pattern is output.
[0023]
The operation of this embodiment will be described with reference to FIG. 5. For example, when the U-phase current i _u that is a component of the load current vector i _out exceeds the current limit level, the limit voltage vector selection unit 174 includes a limit current phase. Information "U phase" is input as information. As a result, the limit voltage vector selection means 174 selects the voltage vector v _out having the maximum magnitude in the direction opposite to the U-phase current i _u (the tip of this voltage vector is indicated by ●) as the limit voltage vector, and The pulse pattern to be output is output.
As in the first embodiment, in order to reduce the current more effectively, the limit voltage vector is switched according to the power supply voltage, and the voltage vector in the direction opposite to the current in the limit current phase is continuously selected. A switching pattern may be output.
[0024]
In the above description, the output voltage vector having the maximum magnitude is selected by the limit voltage vector selection means 173, 174. However, in the present invention, the load current only needs to be reduced from the current limit level. There is no need to select the maximum output voltage vector.
Further, the number of phases of the direct converter 30 is not limited to three phases.
[0025]
ADVANTAGE OF THE INVENTION According to this invention, the driving | operation of a direct conversion type | mold power converter device can be continued, without producing | generating an overcurrent, even if the situation where an overcurrent is likely to generate | occur | produce in a direct conversion type | mold power converter device.
Needless to say, the current limiting means in the present invention can be realized not only by software but also by hardware. However, when implemented by software, if the sampling rate of the CPU is slow, the determination of whether or not the current exceeds the current limit level is delayed, making it difficult to avoid current immediately. In addition, even after determining that the current has exceeded the current limit level, the voltage vector for limiting the current is controlled only by the CPU sampling time, resulting in a delayed response and again avoiding overcurrent immediately. Becomes difficult.
That is, since the current limiting operation depends on the sampling rate of the CPU, it is better to implement it with hardware in order to perform the current limiting at high speed.
[0026]
【The invention's effect】
As described above, according to the present invention, in the direct conversion type power conversion device, even when the load current does not reach the overcurrent level, the current limit can be performed when the current limit level is less than that level. The direct conversion power converter can be continuously operated while avoiding the occurrence of overcurrent.
[Brief description of the drawings]
FIG. 1 is a control block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram showing a first embodiment of load current limiting means in FIG. 1;
FIG. 3 is a diagram for explaining a method of selecting a limited voltage vector in FIG.
4 is a block diagram showing a second embodiment of the load current limiting means in FIG. 1. FIG.
FIG. 5 is a diagram for explaining a method of selecting a limit voltage vector in FIG. 4;
FIG. 6 is a control block diagram showing a conventional technique.
FIG. 7 is a configuration diagram of a matrix converter.
[Explanation of symbols]
10: Voltage command generating means 11: PWM generating means 12: Abnormal processing means 13: Voltage detector 14: Current detector 15: Abnormality detecting means 16: First changeover switch 17, 17 ': Load current limiting means 171: Current Vector detection means 172: Output voltage vector pattern calculation means 173, 174: Limit voltage vector selection means 18: Comparison means 19: Second changeover switch 20: Power supply 30: Direct converter 40: Loads S1 to S9: Bidirectional switch

Claims (2)

In an AC-AC direct conversion type power conversion device including a direct converter that directly converts AC power into AC power using a semiconductor switching element,
Current detection means for detecting a load current of the direct converter;
Comparison means for comparing at least one phase current level of the load current detected by the current detection means with a current limit level smaller than the overcurrent level;
When the comparison means detects that the one phase current level exceeds the current limit level, an output voltage level in a direction almost opposite to the direction of the load current vector is set to reduce the phase current. A load current limiting means for selecting and driving the direct converter with a switching pattern corresponding to the output voltage level;
An AC-AC direct conversion power converter characterized by comprising: In an AC-AC direct conversion type power conversion device including a direct converter that directly converts AC power into AC power using a semiconductor switching element,
Current detection means for detecting a load current of the direct converter;
Comparison means for comparing at least one phase current level of the load current detected by the current detection means with a current limit level smaller than the overcurrent level;
When the comparison means detects that the one phase current level exceeds the current limit level, in order to decrease the phase current, the direction of the phase current vector exceeding the current limit level is substantially Load current limiting means for selecting an output voltage vector in the opposite direction and driving the direct converter with a switching pattern corresponding to the output voltage level;
AC characterized by comprising a - AC direct conversion type power converter.

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