JP4822100B2 - AC / AC direct conversion device - Google Patents

Description

  The present invention relates to an AC / AC direct conversion device that directly converts a multiphase AC voltage to a multiphase AC voltage of an arbitrary frequency using a semiconductor switching element without using a large energy buffer.

FIG. 4 shows the prior art of this type of AC / AC direct conversion device, which is an example of converting a three-phase AC voltage into a three-phase AC voltage of an arbitrary frequency by a matrix converter as a direct converter.
In FIG. 4, 1 is a three-phase AC power source, 2 is an input filter comprising a reactor and a capacitor, 3 is a matrix converter, and 4 is a load such as an electric motor.

  The matrix converter 3 is similar to the U-phase switch 3U composed of three bidirectional switches S having one end connected to the R, S, and T-phase input terminals and the other end collectively connected to the U-phase output terminal. The other end of the V-phase switch 3V is composed of three bidirectional switches S connected to the V-phase output terminal at the same time, and the other is connected to the W-phase output terminal. And a W-phase switch 3W composed of a direction switch S. Note that the bidirectional switch S is configured, for example, by connecting two semiconductor switching elements such as IGBTs in antiparallel as shown in the lower part of FIG. 4, and can pass current in both directions.

  The matrix converter 3 does not use a large energy buffer unlike a converter / inverter system that includes an electrolytic capacitor or the like in the DC intermediate circuit, so it can be reduced in size and weight and can be controlled based on the converter / inverter system. The input / output current can be controlled to a sine wave.

  On the other hand, it is known that the maximum output voltage of the matrix converter is 0.86 times the input voltage, which is inferior in terms of voltage utilization compared to the converter / inverter system. For this reason, if the operation is performed in the overmodulation region, the voltage utilization rate can be increased, but problems such as distortion of the output voltage and torque pulsation of the electric motor as a load occur.

  In view of this point, for example, in Non-Patent Document 1, in an electric motor drive system using a matrix converter, in an overmodulation region, the terminal voltage of the electric motor is controlled by weakening the magnetic flux according to the input voltage of the matrix converter. A control method is described in which distortion of input / output current is suppressed and a voltage larger than that at the time of sinusoidal modulation can be output.

On the other hand, in a power conversion device in which a three-phase AC power source is connected to a multiplex three-phase PWM cycloconverter via a three-phase transformer, the number of controllers for generating PWM pulses is reduced and the three-phase AC power source is asymmetrical. Patent Document 1 discloses a power conversion device that can output a high voltage with less distortion by creating a PWM pulse in consideration of characteristics and pulsation.
Similarly, a three-phase AC power source is connected to a multiplex three-phase PWM cycloconverter via a three-phase transformer to drive a high-voltage AC motor. A power converter that can be generated is described in Patent Document 2.

Ikuya Sato and 5 others, “Study on improvement of motor drive performance of matrix converter”, The Institute of Electrical Engineers of Japan, Semiconductor Power Conversion Study Group, SPC-04-75, 2004 Japanese Patent Laid-Open No. 11-252992 ([0017] to [0019], [0029], FIG. 1, FIG. 9 etc.) Japanese Patent Laying-Open No. 2005-45999 ([0023] to [0028], FIGS. 1, 5, etc.)

  If the technique disclosed in Non-Patent Document 1 described above is used, there is no fear that a large distortion occurs in the input / output current in the overmodulation region, but the distortion increases compared to the case of sine wave modulation, and the converter / inverter system Compared with, the drive characteristics of the electric motor are deteriorated. Further, the control in the overmodulation region is generally complicated, and there are problems such as a complicated circuit configuration of the control device and an increase in cost.

  For this reason, when driving a motor with a matrix converter, it may be possible to lower the voltage rating of the motor to such an extent that operation in the overmodulation region is unnecessary, but the voltage rating has been lowered to obtain the same output. There are inconveniences such as an increase in current rating and the need for a dedicated electric motor, which limit the application of the matrix converter.

Therefore, the problem to be solved by the present invention is that the input voltage of the direct converter is boosted by a single transformer provided between the polyphase AC power source and the direct converter, and the maximum output is not required in the overmodulation region. The object is to provide an AC / AC direct conversion device with increased voltage.
Note that Patent Documents 1 and 2 do not disclose any idea of directly boosting the input voltage of a converter using a single-turn transformer.

In order to solve the above-mentioned problem, the invention described in claim 1 is an AC / AC direct circuit including a direct converter that directly converts a multi-phase AC voltage of an AC power source into a multi-phase AC voltage of an arbitrary frequency using a semiconductor switching element. In the conversion device,
A self-winding transformer is connected between the AC power source and the direct converter, and a leakage inductance of the self-winding transformer is used as an input filter reactor. Directly supplied to the converter.

The invention described in claim 2, Oite the AC AC direct conversion device according to claim 1, so that the maximum output voltage of the direct converter is equal to the supply voltage, the power supply voltage by said autotransformer Boosts the voltage.

The invention described in claim 3, Oite the AC AC direct conversion device according to claim 1 or 2, wherein the autotransformer is shall use a multi-phase autotransformer.

According to the present invention, the maximum output voltage of a direct converter such as a matrix converter can be increased without operating in an overmodulation region. For this reason, measures such as lowering the voltage rating of the electric motor as a load or using a dedicated electric motor are not required, and the versatility of the matrix converter is not hindered. At the same time, distortion of the output voltage and input / output current of the direct converter can be reduced.
In addition, since the auto-transformer is used for boosting the input voltage of the direct converter, the entire device can be reduced in size and cost compared to the case of using a normal transformer, and the auto-transformer can be reduced. The leakage inductance of the vessel can also be used as an input filter reactor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. The same components as those in FIG. 4 are given the same reference numerals and detailed description thereof is omitted, and different portions will be mainly described below.

In FIG. 1, a Y-connected input filter capacitor 6 is connected to input terminals R, S, and T of a matrix converter 3 as a direct converter, and a three-phase AC power source 1 and the input terminals R, S, and T are connected. A self-winding transformer 5 is connected to T.
Here, FIG. 2 shows the configuration of the autotransformer 5, 5 r, 5 s, 5 t are Y-connected windings connected to the input terminals R, S, T of the matrix converter 3, R ′, S ′. , T ′ are terminals on the three-phase AC power source 1 side.
2A shows an example in which the autotransformer 5 is constituted by a three-phase autotransformer. FIG. 2B shows the autotransformer 5 by three single-phase autotransformers 5R, 5S, and 5T. In this case, the same effect can be obtained in any case.

Here, referring to FIG. 3, the operation principle of the single-phase single-winding transformer will be described below in comparison with a normal two-winding transformer. FIG. 3A is a circuit diagram of a two-winding transformer, and FIG. 3B is a circuit diagram of a single-winding transformer.
In the single-winding transformer of FIG. 3 (b), as is well known, the common part (between B and C) of the winding is called a shunt winding, and the non-common part (between A and B) is called a series winding. When the number of turns of the path winding is N ₁ and the total number of turns is N ₂ , the voltage V ₁ applied to the shunt winding and the voltage V ₂ induced in the entire winding (between AC) are between There is a relationship of Formula 1.
[Formula 1]
_{V 1 / V 2 = N 1} / N 2 = a

If the current flowing in the primary side of the autotransformer is I ₁ , the current flowing in the secondary side is I _2, and the exciting current of the winding is ignored, Equations 2 and 3 are established.
[Formula 2]
N ₁ (I ₁ −I ₂ ) = (N ₂ −N ₁ ) I ₂
[Formula 3]
_{I 1 / I 2 = N 2} / N 1 = 1 / a
The relations of the above formulas 1 to 3 are the same in the two-winding transformer of FIG.

Here, the current I flowing through the shunt winding in the autotransformer is expressed by Equation 4.
[Formula 4]
I = I ₁ −I ₂ = (1-a) I ₁

Equation 4 shows that only the difference between the primary current I ₁ and the secondary current I ₂ flows in the shunt winding, and when the turn ratio is close to 1, the current I becomes almost zero. It is possible to reduce the size of the winding and thus the size of the transformer. In addition, since the primary winding and the secondary winding are partially shared, the volume can be greatly reduced as compared with a normal transformer, and also in this respect, downsizing can be achieved. Therefore, it can be said that the auto-transformer is suitable for a transformer having a small amount of boosting.

  On the other hand, as described above, since the maximum output voltage of the matrix converter is 0.86 times the input voltage, if the power supply voltage is boosted by a transformer and input to the matrix converter, the voltage range that can be output by the matrix converter is The power supply voltage can be expanded. However, when boosting using a normal three-phase transformer, the size of the transformer is large, leading to an increase in size and cost of the entire apparatus.

Therefore, in the present embodiment, the power supply voltage is boosted by the single-wound transformer 5 that is optimal for an application with a small boosting ratio and input to the matrix converter 3, so that the maximum output voltage reaches the power supply voltage of the three-phase AC power supply 1. It is intended to increase.
In order to obtain the maximum output voltage equivalent to that of the conventional converter / inverter system when a matrix converter is used as a direct converter, the power supply voltage may be boosted by about 15% and input to the matrix converter. As a transformer for a transformer, a single-winding transformer is optimal when considering miniaturization.

When boosting the power supply voltage by about 15%, it is sufficient to use an autotransformer having a turn ratio a of 0.85 in Equation 1, and the current I flowing in the shunt winding of the autotransformer at that time is given by Equation 4. Therefore, the shunt winding can be downsized because only 15% of the input current I ₁ is required. In addition, although a current substantially equal to the input current flows through the series winding, the increase in the volume of the series winding is not a problem because the boosted amount is 15%.

  Specifically, the autotransformer 5 shown in FIG. 2 is connected between the three-phase AC power source 1 and the input terminals R, S, T of the matrix converter 3 as shown in FIG. By setting the turns ratio a to 0.85, the line voltage of the three-phase AC power source 1 can be boosted by about 15% and input to the matrix converter 3, and the matrix converter 3 is operated by sinusoidal modulation. The output voltage can be increased and distortion of the output voltage and input / output current can be reduced.

As a result, the circuit configuration associated with the control in the overmodulation region is not complicated and the cost is not increased, and it is not necessary to lower the voltage rating of the motor as the load 4 or use a dedicated motor. There is no worry of sacrificing versatility.
Furthermore, according to this embodiment, since the leakage inductance of the autotransformer 5 can be used as an input filter reactor, there is no need to provide a separate input filter reactor. This can contribute to cost reduction.

It is a block diagram which shows embodiment of this invention. It is a block diagram of the autotransformer in FIG. It is a circuit diagram of a double winding transformer and a single winding transformer. It is a block diagram which shows a prior art.

Explanation of symbols

1: Three-phase AC power supply 3: Matrix converter 3U: U-phase switch 3V: V-phase switch 3W: W-phase switch 4: Load 5: Single transformer 5r, 5s, 5t: Winding 5R, 5S, 5T: Single phase Autotransformer S: Bidirectional switch

Claims (3)

In an AC / AC direct conversion device including a direct converter that directly converts a multi-phase AC voltage of an AC power source into a multi-phase AC voltage of an arbitrary frequency using a semiconductor switching element,
A self-winding transformer is connected between the AC power source and the direct converter, and a leakage inductance of the self-winding transformer is used as an input filter reactor. An AC / AC direct conversion device characterized by being supplied to a direct converter. In the AC / AC direct conversion device according to claim 1,
An AC / AC direct conversion device characterized in that the power supply voltage is boosted by the autotransformer so that the maximum output voltage of the direct converter becomes equal to the power supply voltage. In the AC / AC direct conversion device according to claim 1 or 2,
Examples autotransformer, the AC AC direct conversion device, wherein Rukoto using polyphase autotransformer.

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